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//: You guessed right: the '000' prefix means you should start reading here.
//:
//: This project is set up to load all files with a numeric prefix. Just
//: create a new file and start hacking.
//:
//: The first few files (00*) are independent of what this program does, an
//: experimental skeleton that will hopefully make it both easier for others to
//: understand and more malleable, easier to rewrite and remould into radically
//: different shapes without breaking in subtle corner cases. The premise is
//: that understandability and rewrite-friendliness are related in a virtuous
//: cycle. Doing one well makes it easier to do the other.
//:
//: Lower down, this file contains a legal, bare-bones C++ program. It doesn't
//: do anything yet; subsequent files will contain :(...) directives to insert
//: lines into it. For example:
//:   :(after "more events")
//: This directive means: insert the following lines after a line in the
//: program containing the words "more events".
//:
//: A simple tool is included to 'tangle' all the files together in sequence
//: according to their directives into a single source file containing all the
//: code for the project, and then feed the source file to the compiler.
//: (It'll drop these comments starting with a '//:' prefix that only make
//: sense before tangling.)
//:
//: Directives free up the programmer to order code for others to read rather
//: than as forced by the computer or compiler. Each individual feature can be
//: organized in a self-contained 'layer' that adds code to many different data
//: structures and functions all over the program. The right decomposition into
//: layers will let each layer make sense in isolation.
//:
//:   "If I look at any small part of it, I can see what is going on -- I don't
//:   need to refer to other parts to understand what something is doing.
//:
//:   If I look at any large part in overview, I can see what is going on -- I
//:   don't need to know all the details to get it.
//:
//:   Every level of detail is as locally coherent and as well thought-out as
//:   any other level."
//:
//:       -- Richard Gabriel, "The Quality Without A Name"
//:          (http://dreamsongs.com/Files/PatternsOfSoftware.pdf, page 42)
//:
//: Directives are powerful; they permit inserting or modifying any point in
//: the program. Using them tastefully requires mapping out specific lines as
//: waypoints for future layers to hook into. Often such waypoints will be in
//: comments, capitalized to hint that other layers rely on their presence.
//:
//: A single waypoint might have many different code fragments hooking into
//: it from all over the codebase. Use 'before' directives to insert
//: code at a location in order, top to bottom, and 'after' directives to
//: insert code in reverse order. By convention waypoints intended for insertion
//: before begin with 'End'. Notice below how the layers line up above the "End
//: Foo" waypoint.
//:
//:   File 001          File 002                File 003
//:   ============      ===================     ===================
//:   // Foo
//:   ------------
//:              <----  :(before "End Foo")
//:                     ....
//:                     ...
//:   ------------
//:              <----------------------------  :(before "End Foo")
//:                                             ....
//:                                             ...
//:   // End Foo
//:   ============
//:
//: Here's part of a layer in color: http://i.imgur.com/0eONnyX.png. Directives
//: are shaded dark.
//:
//: Layers do more than just shuffle code around. In a well-organized codebase
//: it should be possible to stop loading after any file/layer, build and run
//: the program, and pass all tests for loaded features. (Relevant is
//: http://youtube.com/watch?v=c8N72t7aScY, a scene from "2001: A Space
//: Odyssey".) Get into the habit of running the included script called
//: 'test_layers' before you commit any changes.
//:
//: This 'subsetting guarantee' ensures that this directory contains a
//: cleaned-up narrative of the evolution of this codebase. Organizing
//: autobiographically allows newcomers to rapidly orient themselves, reading
//: the first few files to understand a simple gestalt of a program's core
//: purpose and features, and later gradually working their way through other
//: features as the need arises.
//:
//: Programmers shouldn't need to understand everything about a program to
//: hack on it. But they shouldn't be prevented from a thorough understanding
//: of each aspect either. The goal of layers is to reward curiosity.

// Includes
// End Includes

// Types
// End Types

// Function prototypes are auto-generated in the 'build*' scripts; define your
// functions in any order. Just be sure to declare each function header all on
// one line, ending with the '{'. Our auto-generation scripts are too minimal
// and simple-minded to handle anything else.
#include "function_list"  // by convention, files ending with '_list' are auto-generated

// Globals
//
// All statements in this section should always define a single variable on a
// single line. The 'build*' scripts will simple-mindedly auto-generate extern
// declarations for them. Remember to define (not just declare) constants with
// extern linkage in this section, since C++ global constants have internal
// linkage by default.
//
// End Globals

int main(int argc, char* argv[]) {
  atexit(reset);

  // End One-time Setup

  // Commandline Parsing
  // End Commandline Parsing

  return 0;  // End Main
}

// Unit Tests
// End Unit Tests

//: our first directive; insert the following header at the start of the program
:(before "End Includes")
#include <stdlib.h>

//: Without directives or with the :(code) directive, lines get added at the
//: end.
:(code)
void reset() {
  // End Reset
}
64'>964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194
## running code from the editor and creating sandboxes
#
# Running code in the sandbox editor prepends its contents to a list of
# (non-editable) sandboxes below the editor, showing the result and a maybe
# few other things.
#
# This layer draws the menubar buttons non-editable sandboxes but they don't
# do anything yet. Later layers implement each button.

def! main [
  local-scope
  open-console
  initial-recipe:text <- restore [recipes.mu]
  initial-sandbox:text <- new []
  hide-screen 0/screen
  env:address:programming-environment-data <- new-programming-environment 0/screen, initial-recipe, initial-sandbox
  env <- restore-sandboxes env
  render-all 0/screen, env, render
  event-loop 0/screen, 0/console, env
  # never gets here
]

container programming-environment-data [
  sandbox:address:sandbox-data  # list of sandboxes, from top to bottom
  render-from:number
  number-of-sandboxes:number
]

after <programming-environment-initialization> [
  *result <- put *result, render-from:offset, -1
]

container sandbox-data [
  data:text
  response:text
  # coordinates to track clicks
  # constraint: will be 0 for sandboxes at positions before env.render-from
  starting-row-on-screen:number
  code-ending-row-on-screen:number  # past end of code
  screen:address:screen  # prints in the sandbox go here
  next-sandbox:address:sandbox-data
]

scenario run-and-show-results [
  trace-until 100/app  # trace too long
  assume-screen 100/width, 15/height
  # recipe editor is empty
  1:text <- new []
  # sandbox editor contains an instruction without storing outputs
  2:text <- new [divide-with-remainder 11, 3]
  3:address:programming-environment-data <- new-programming-environment screen:address:screen, 1:text, 2:text
  # run the code in the editors
  assume-console [
    press F4
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  ]
  # check that screen prints the results
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  0   edit          copy            delete         .
    .                                                  divide-with-remainder 11, 3                      .
    .                                                  3                                                .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
  screen-should-contain-in-color 7/white, [
    .                                                                                                    .
    .                                                                                                    .
    .                                                                                                    .
    .                                                                                                    .
    .                                                   divide-with-remainder 11, 3                      .
    .                                                                                                    .
    .                                                                                                    .
    .                                                                                                    .
    .                                                                                                    .
  ]
  screen-should-contain-in-color 245/grey, [
    .                                                                                                    .
    .                                                                                                   .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
    .                                                                                                   .
    .                                                  3                                                .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
  # sandbox menu in reverse video
  screen-should-contain-in-color 232/black, [
    .                                                                                                    .
    .                                                                                                    .
    .                                                                                                    .
    .                                                   0   edit          copy            delete         .
  ]
  # run another command
  assume-console [
    left-click 1, 80
    type [add 2, 2]
    press F4
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  ]
  # check that screen prints the results
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  0   edit          copy            delete         .
    .                                                  add 2, 2                                         .
    .                                                  4                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  1   edit          copy            delete         .
    .                                                  divide-with-remainder 11, 3                      .
    .                                                  3                                                .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
]

after <global-keypress> [
  # F4? load all code and run all sandboxes.
  {
    do-run?:boolean <- equal k, 65532/F4
    break-unless do-run?
    screen <- update-status screen, [running...       ], 245/grey
    error?:boolean, env, screen <- run-sandboxes env, screen
    # F4 might update warnings and results on both sides
    screen <- render-all screen, env, render
    {
      break-if error?
      screen <- update-status screen, [                 ], 245/grey
    }
    screen <- update-cursor screen, recipes, current-sandbox, sandbox-in-focus?, env
    loop +next-event:label
  }
]

def run-sandboxes env:address:programming-environment-data, screen:address:screen -> errors-found?:boolean, env:address:programming-environment-data, screen:address:screen [
  local-scope
  load-ingredients
  errors-found?:boolean, env, screen <- update-recipes env, screen
  return-if errors-found?
  # check contents of right editor (sandbox)
  <run-sandboxes-begin>
  current-sandbox:address:editor-data <- get *env, current-sandbox:offset
  {
    sandbox-contents:text <- editor-contents current-sandbox
    break-unless sandbox-contents
    # if contents exist, first save them
    # run them and turn them into a new sandbox-data
    new-sandbox:address:sandbox-data <- new sandbox-data:type
    *new-sandbox <- put *new-sandbox, data:offset, sandbox-contents
    # push to head of sandbox list
    dest:address:sandbox-data <- get *env, sandbox:offset
    *new-sandbox <- put *new-sandbox, next-sandbox:offset, dest
    *env <- put *env, sandbox:offset, new-sandbox
    # update sandbox count
    sandbox-count:number <- get *env, number-of-sandboxes:offset
    sandbox-count <- add sandbox-count, 1
    *env <- put *env, number-of-sandboxes:offset, sandbox-count
    # clear sandbox editor
    init:address:duplex-list:character <- push 167/§, 0/tail
    *current-sandbox <- put *current-sandbox, data:offset, init
    *current-sandbox <- put *current-sandbox, top-of-screen:offset, init
  }
  # save all sandboxes before running, just in case we die when running
  save-sandboxes env
  # run all sandboxes
  curr:address:sandbox-data <- get *env, sandbox:offset
  idx:number <- copy 0
  {
    break-unless curr
    curr <- update-sandbox curr, env, idx
    curr <- get *curr, next-sandbox:offset
    idx <- add idx, 1
    loop
  }
  <run-sandboxes-end>
]

# copy code from recipe editor, persist, load into mu
# replaced in a later layer (whereupon errors-found? will actually be set)
def update-recipes env:address:programming-environment-data, screen:address:screen -> errors-found?:boolean, env:address:programming-environment-data, screen:address:screen [
  local-scope
  load-ingredients
  recipes:address:editor-data <- get *env, recipes:offset
  in:text <- editor-contents recipes
  save [recipes.mu], in  # newlayer: persistence
  reload in
  errors-found? <- copy 0/false
]

# replaced in a later layer
def! update-sandbox sandbox:address:sandbox-data, env:address:programming-environment-data, idx:number -> sandbox:address:sandbox-data, env:address:programming-environment-data [
  local-scope
  load-ingredients
  data:text <- get *sandbox, data:offset
  response:text, _, fake-screen:address:screen <- run-sandboxed data
  *sandbox <- put *sandbox, response:offset, response
  *sandbox <- put *sandbox, screen:offset, fake-screen
]

def update-status screen:address:screen, msg:text, color:number -> screen:address:screen [
  local-scope
  load-ingredients
  screen <- move-cursor screen, 0, 2
  screen <- print screen, msg, color, 238/grey/background
]

def save-sandboxes env:address:programming-environment-data [
  local-scope
  load-ingredients
  current-sandbox:address:editor-data <- get *env, current-sandbox:offset
  # first clear previous versions, in case we deleted some sandbox
  $system [rm lesson/[0-9]* >/dev/null 2>/dev/null]  # some shells can't handle '>&'
  curr:address:sandbox-data <- get *env, sandbox:offset
  idx:number <- copy 0
  {
    break-unless curr
    data:text <- get *curr, data:offset
    filename:text <- to-text idx
    save filename, data
    <end-save-sandbox>
    idx <- add idx, 1
    curr <- get *curr, next-sandbox:offset
    loop
  }
]

def! render-sandbox-side screen:address:screen, env:address:programming-environment-data, {render-editor: (recipe (address screen) (address editor-data) -> number number (address screen) (address editor-data))} -> screen:address:screen, env:address:programming-environment-data [
  local-scope
  load-ingredients
  trace 11, [app], [render sandbox side]
  current-sandbox:address:editor-data <- get *env, current-sandbox:offset
  row:number, column:number <- copy 1, 0
  left:number <- get *current-sandbox, left:offset
  right:number <- get *current-sandbox, right:offset
  # render sandbox editor
  render-from:number <- get *env, render-from:offset
  {
    render-current-sandbox?:boolean <- equal render-from, -1
    break-unless render-current-sandbox?
    row, column, screen, current-sandbox <- call render-editor, screen, current-sandbox
    clear-screen-from screen, row, column, left, right
    row <- add row, 1
  }
  # render sandboxes
  draw-horizontal screen, row, left, right, 9473/horizontal-double
  sandbox:address:sandbox-data <- get *env, sandbox:offset
  row, screen <- render-sandboxes screen, sandbox, left, right, row, render-from
  clear-rest-of-screen screen, row, left, right
]

def render-sandboxes screen:address:screen, sandbox:address:sandbox-data, left:number, right:number, row:number, render-from:number, idx:number -> row:number, screen:address:screen, sandbox:address:sandbox-data [
  local-scope
  load-ingredients
  return-unless sandbox
  screen-height:number <- screen-height screen
  at-bottom?:boolean <- greater-or-equal row, screen-height
  return-if at-bottom?:boolean
  hidden?:boolean <- lesser-than idx, render-from
  {
    break-if hidden?
    # render sandbox menu
    row <- add row, 1
    screen <- move-cursor screen, row, left
    screen <- render-sandbox-menu screen, idx, left, right
    # save menu row so we can detect clicks to it later
    *sandbox <- put *sandbox, starting-row-on-screen:offset, row
    # render sandbox contents
    row <- add row, 1
    screen <- move-cursor screen, row, left
    sandbox-data:text <- get *sandbox, data:offset
    row, screen <- render-code screen, sandbox-data, left, right, row
    *sandbox <- put *sandbox, code-ending-row-on-screen:offset, row
    # render sandbox warnings, screen or response, in that order
    sandbox-response:text <- get *sandbox, response:offset
    <render-sandbox-results>
    {
      sandbox-screen:address:screen <- get *sandbox, screen:offset
      empty-screen?:boolean <- fake-screen-is-empty? sandbox-screen
      break-if empty-screen?
      row, screen <- render-screen screen, sandbox-screen, left, right, row
    }
    {
      break-unless empty-screen?
      <render-sandbox-response>
      row, screen <- render-text screen, sandbox-response, left, right, 245/grey, row
    }
    +render-sandbox-end
    at-bottom?:boolean <- greater-or-equal row, screen-height
    return-if at-bottom?
    # draw solid line after sandbox
    draw-horizontal screen, row, left, right, 9473/horizontal-double
  }
  # if hidden, reset row attributes
  {
    break-unless hidden?
    *sandbox <- put *sandbox, starting-row-on-screen:offset, 0
    *sandbox <- put *sandbox, code-ending-row-on-screen:offset, 0
    <end-render-sandbox-reset-hidden>
  }
  # draw next sandbox
  next-sandbox:address:sandbox-data <- get *sandbox, next-sandbox:offset
  next-idx:number <- add idx, 1
  row, screen <- render-sandboxes screen, next-sandbox, left, right, row, render-from, next-idx
]

def render-sandbox-menu screen:address:screen, sandbox-index:number, left:number, right:number -> screen:address:screen [
  local-scope
  load-ingredients
  move-cursor-to-column screen, left
  edit-button-left:number, edit-button-right:number, copy-button-left:number, copy-button-right:number, delete-button-left:number <- sandbox-menu-columns left, right
  print screen, sandbox-index, 232/dark-grey, 245/grey
  start-buttons:number <- subtract edit-button-left, 1
  clear-line-until screen, start-buttons, 245/grey
  print screen, [edit], 232/black, 94/background-orange
  clear-line-until screen, edit-button-right, 94/background-orange
  _, col:number <- cursor-position screen
  at-start-of-copy-button?:boolean <- equal col, copy-button-left
  assert at-start-of-copy-button?, [aaa]
  print screen, [copy], 232/black, 58/background-green
  clear-line-until screen, copy-button-right, 58/background-green
  _, col:number <- cursor-position screen
  at-start-of-delete-button?:boolean <- equal col, delete-button-left
  assert at-start-of-delete-button?, [bbb]
  print screen, [delete], 232/black, 52/background-red
  clear-line-until screen, right, 52/background-red
]

# divide up the menu bar for a sandbox into 3 segments, for edit/copy/delete buttons
# delete-button-right == right
# all left/right pairs are inclusive
def sandbox-menu-columns left:number, right:number -> edit-button-left:number, edit-button-right:number, copy-button-left:number, copy-button-right:number, delete-button-left:number [
  local-scope
  load-ingredients
  start-buttons:number <- add left, 4/space-for-sandbox-index
  buttons-space:number <- subtract right, start-buttons
  button-width:number <- divide-with-remainder buttons-space, 3  # integer division
  buttons-wide-enough?:boolean <- greater-or-equal button-width, 8
  assert buttons-wide-enough?, [sandbox must be at least 30 or so characters wide]
  edit-button-left:number <- copy start-buttons
  copy-button-left:number <- add start-buttons, button-width
  edit-button-right:number <- subtract copy-button-left, 1
  delete-button-left:number <- subtract right, button-width
  copy-button-right:number <- subtract delete-button-left, 1
]

# print a text 's' to 'editor' in 'color' starting at 'row'
# clear rest of last line, move cursor to next line
def render-text screen:address:screen, s:text, left:number, right:number, color:number, row:number -> row:number, screen:address:screen [
  local-scope
  load-ingredients
  return-unless s
  column:number <- copy left
  screen <- move-cursor screen, row, column
  screen-height:number <- screen-height screen
  i:number <- copy 0
  len:number <- length *s
  {
    +next-character
    done?:boolean <- greater-or-equal i, len
    break-if done?
    done? <- greater-or-equal row, screen-height
    break-if done?
    c:character <- index *s, i
    {
      # at right? wrap.
      at-right?:boolean <- equal column, right
      break-unless at-right?
      # print wrap icon
      wrap-icon:character <- copy 8617/loop-back-to-left
      print screen, wrap-icon, 245/grey
      column <- copy left
      row <- add row, 1
      screen <- move-cursor screen, row, column
      loop +next-character:label  # retry i
    }
    i <- add i, 1
    {
      # newline? move to left rather than 0
      newline?:boolean <- equal c, 10/newline
      break-unless newline?
      # clear rest of line in this window
      {
        done?:boolean <- greater-than column, right
        break-if done?
        space:character <- copy 32/space
        print screen, space
        column <- add column, 1
        loop
      }
      row <- add row, 1
      column <- copy left
      screen <- move-cursor screen, row, column
      loop +next-character:label
    }
    print screen, c, color
    column <- add column, 1
    loop
  }
  was-at-left?:boolean <- equal column, left
  clear-line-until screen, right
  {
    break-if was-at-left?
    row <- add row, 1
  }
  move-cursor screen, row, left
]

# assumes programming environment has no sandboxes; restores them from previous session
def restore-sandboxes env:address:programming-environment-data -> env:address:programming-environment-data [
  local-scope
  load-ingredients
  # read all scenarios, pushing them to end of a list of scenarios
  idx:number <- copy 0
  curr:address:sandbox-data <- copy 0
  prev:address:sandbox-data <- copy 0
  {
    filename:text <- to-text idx
    contents:text <- restore filename
    break-unless contents  # stop at first error; assuming file didn't exist
                           # todo: handle empty sandbox
    # create new sandbox for file
    curr <- new sandbox-data:type
    *curr <- put *curr, data:offset, contents
    <end-restore-sandbox>
    {
      break-if idx
      *env <- put *env, sandbox:offset, curr
    }
    {
      break-unless idx
      *prev <- put *prev, next-sandbox:offset, curr
    }
    idx <- add idx, 1
    prev <- copy curr
    loop
  }
  # update sandbox count
  *env <- put *env, number-of-sandboxes:offset, idx
]

# print the fake sandbox screen to 'screen' with appropriate delimiters
# leave cursor at start of next line
def render-screen screen:address:screen, sandbox-screen:address:screen, left:number, right:number, row:number -> row:number, screen:address:screen [
  local-scope
  load-ingredients
  return-unless sandbox-screen
  # print 'screen:'
  row <- render-text screen, [screen:], left, right, 245/grey, row
  screen <- move-cursor screen, row, left
  # start printing sandbox-screen
  column:number <- copy left
  s-width:number <- screen-width sandbox-screen
  s-height:number <- screen-height sandbox-screen
  buf:address:array:screen-cell <- get *sandbox-screen, data:offset
  stop-printing:number <- add left, s-width, 3
  max-column:number <- min stop-printing, right
  i:number <- copy 0
  len:number <- length *buf
  screen-height:number <- screen-height screen
  {
    done?:boolean <- greater-or-equal i, len
    break-if done?
    done? <- greater-or-equal row, screen-height
    break-if done?
    column <- copy left
    screen <- move-cursor screen, row, column
    # initial leader for each row: two spaces and a '.'
    space:character <- copy 32/space
    print screen, space, 245/grey
    print screen, space, 245/grey
    full-stop:character <- copy 46/period
    print screen, full-stop, 245/grey
    column <- add left, 3
    {
      # print row
      row-done?:boolean <- greater-or-equal column, max-column
      break-if row-done?
      curr:screen-cell <- index *buf, i
      c:character <- get curr, contents:offset
      color:number <- get curr, color:offset
      {
        # damp whites down to grey
        white?:boolean <- equal color, 7/white
        break-unless white?
        color <- copy 245/grey
      }
      print screen, c, color
      column <- add column, 1
      i <- add i, 1
      loop
    }
    # print final '.'
    print screen, full-stop, 245/grey
    column <- add column, 1
    {
      # clear rest of current line
      line-done?:boolean <- greater-than column, right
      break-if line-done?
      print screen, space
      column <- add column, 1
      loop
    }
    row <- add row, 1
    loop
  }
]

scenario run-updates-results [
  trace-until 100/app  # trace too long
  assume-screen 100/width, 12/height
  # define a recipe (no indent for the 'add' line below so column numbers are more obvious)
  1:text <- new [ 
recipe foo [
local-scope
z:number <- add 2, 2
reply z
]]
  # sandbox editor contains an instruction without storing outputs
  2:text <- new [foo]
  3:address:programming-environment-data <- new-programming-environment screen:address:screen, 1:text, 2:text
  # run the code in the editors
  assume-console [
    press F4
  ]
  event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .recipe foo [                                      ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .local-scope                                       0   edit          copy            delete         .
    .z:number <- add 2, 2                              foo                                              .
    .reply z                                           4                                                .
    .]                                                 ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
    .                                                                                                   .
  ]
  # make a change (incrementing one of the args to 'add'), then rerun
  assume-console [
    left-click 4, 28  # one past the value of the second arg
    press backspace
    type [3]
    press F4
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  ]
  # check that screen updates the result on the right
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .recipe foo [                                      ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .local-scope                                       0   edit          copy            delete         .
    .z:number <- add 2, 3                              foo                                              .
    .reply z                                           5                                                .
    .]                                                 ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
    .                                                                                                   .
  ]
]

scenario run-instruction-manages-screen-per-sandbox [
  trace-until 100/app  # trace too long
  assume-screen 100/width, 20/height
  # left editor is empty
  1:text <- new []
  # right editor contains an instruction
  2:text <- new [print-integer screen, 4]
  3:address:programming-environment-data <- new-programming-environment screen:address:screen, 1:text, 2:text
  # run the code in the editor
  assume-console [
    press F4
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  ]
  # check that it prints a little toy screen
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  0   edit          copy            delete         .
    .                                                  print-integer screen, 4                          .
    .                                                  screen:                                          .
    .                                                    .4                             .               .
    .                                                    .                              .               .
    .                                                    .                              .               .
    .                                                    .                              .               .
    .                                                    .                              .               .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
]

def editor-contents editor:address:editor-data -> result:text [
  local-scope
  load-ingredients
  buf:address:buffer <- new-buffer 80
  curr:address:duplex-list:character <- get *editor, data:offset
  # skip § sentinel
  assert curr, [editor without data is illegal; must have at least a sentinel]
  curr <- next curr
  return-unless curr, 0
  {
    break-unless curr
    c:character <- get *curr, value:offset
    buf <- append buf, c
    curr <- next curr
    loop
  }
  result <- buffer-to-array buf
]

scenario editor-provides-edited-contents [
  assume-screen 10/width, 5/height
  1:text <- new [abc]
  2:address:editor-data <- new-editor 1:text, screen:address:screen, 0/left, 10/right
  assume-console [
    left-click 1, 2
    type [def]
  ]
  run [
    editor-event-loop screen:address:screen, console:address:console, 2:address:editor-data
    3:text <- editor-contents 2:address:editor-data
    4:array:character <- copy *3:text
  ]
  memory-should-contain [
    4:array:character <- [abdefc]
  ]
]

# keep the bottom of recipes from scrolling off the screen

scenario scrolling-down-past-bottom-of-recipe-editor [
  local-scope
  trace-until 100/app
  assume-screen 100/width, 10/height
  env:address:programming-environment-data <- new-programming-environment screen:address:screen, [], []
  render-all screen, env, render
  assume-console [
    press enter
    press down-arrow
  ]
  event-loop screen, console:address:console, env
  # no scroll
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
    .                                                                                                   .
  ]
]

scenario cursor-down-in-recipe-editor [
  local-scope
  trace-until 100/app
  assume-screen 100/width, 10/height
  env:address:programming-environment-data <- new-programming-environment screen:address:screen, [], []
  render-all screen, env, render
  assume-console [
    press enter
    press up-arrow
    press down-arrow  # while cursor isn't at bottom
  ]
  event-loop screen, console:address:console, env
  cursor:character <- copy 9251/  print screen:address:screen, cursor
  # cursor moves back to bottom
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .                                                 ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
    .                                                                                                   .
  ]
]

# we'll not use the recipe-editor's 'bottom' element directly, because later
# layers will add other stuff to the left side below the editor (error messages)

container programming-environment-data [
  recipe-bottom:number
]

after <render-recipe-components-end> [
  *env <- put *env, recipe-bottom:offset, row
]

after <global-keypress> [
  {
    break-if sandbox-in-focus?
    down-arrow?:boolean <- equal k, 65516/down-arrow
    break-unless down-arrow?
    recipe-editor:address:editor-data <- get *env, recipes:offset
    recipe-cursor-row:number <- get *recipe-editor, cursor-row:offset
    recipe-editor-bottom:number <- get *recipe-editor, bottom:offset
    at-bottom-of-editor?:boolean <- greater-or-equal recipe-cursor-row, recipe-editor-bottom
    break-unless at-bottom-of-editor?
    more-to-scroll?:boolean <- more-to-scroll? env, screen
    break-if more-to-scroll?
    loop +next-event:label
  }
  {
    break-if sandbox-in-focus?
    page-down?:boolean <- equal k, 65518/page-down
    break-unless page-down?
    more-to-scroll?:boolean <- more-to-scroll? env, screen
    break-if more-to-scroll?
    loop +next-event:label
  }
]

after <global-type> [
  {
    break-if sandbox-in-focus?
    page-down?:boolean <- equal k, 6/ctrl-f
    break-unless page-down?
    more-to-scroll?:boolean <- more-to-scroll? env, screen
    break-if more-to-scroll?
    loop +next-event:label
  }
]

def more-to-scroll? env:address:programming-environment-data, screen:address:screen -> result:boolean [
  local-scope
  load-ingredients
  recipe-bottom:number <- get *env, recipe-bottom:offset
  height:number <- screen-height screen
  result <- greater-or-equal recipe-bottom, height
]

scenario scrolling-down-past-bottom-of-recipe-editor-2 [
  local-scope
  trace-until 100/app
  assume-screen 100/width, 10/height
  env:address:programming-environment-data <- new-programming-environment screen:address:screen, [], []
  render-all screen, env, render
  assume-console [
    # add a line
    press enter
    # cursor back to top line
    press up-arrow
    # try to scroll
    press page-down  # or ctrl-f
  ]
  event-loop screen, console:address:console, env
  # no scroll, and cursor remains at top line
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊                                                 .
    .                                                                                                   .
  ]
]

scenario scrolling-down-past-bottom-of-recipe-editor-3 [
  local-scope
  trace-until 100/app
  assume-screen 100/width, 10/height
  env:address:programming-environment-data <- new-programming-environment screen:address:screen, [], [ab
cd]
  render-all screen, env, render
  assume-console [
    # add a line
    press enter
    # switch to sandbox
    press ctrl-n
    # move cursor
    press down-arrow
  ]
  event-loop screen, console:address:console, env
  cursor:character <- copy 9251/  print screen:address:screen, cursor
  # no scroll on recipe side, cursor moves on sandbox side
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ab                                               .
    .                                                  ┊␣d                                               .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
]

# scrolling through sandboxes

scenario scrolling-down-past-bottom-of-sandbox-editor [
  trace-until 100/app  # trace too long
  assume-screen 100/width, 10/height
  # initialize sandbox side
  1:text <- new []
  2:text <- new [add 2, 2]
  3:address:programming-environment-data <- new-programming-environment screen:address:screen, 1:text, 2:text
  render-all screen, 3:address:programming-environment-data, render
  assume-console [
    # create a sandbox
    press F4
  ]
  event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  0   edit          copy            delete         .
    .                                                  add 2, 2                                         .
  ]
  # switch to sandbox window and hit 'page-down'
  assume-console [
    press ctrl-n
    press page-down
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
    4:character/cursor <- copy 9251/    print screen:address:screen, 4:character/cursor
  ]
  # sandbox editor hidden; first sandbox displayed
  # cursor moves to first sandbox
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊␣   edit          copy            delete         .
    .                                                  add 2, 2                                         .
    .                                                  4                                                .
  ]
  # hit 'page-up'
  assume-console [
    press page-up
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
    4:character/cursor <- copy 9251/    print screen:address:screen, 4:character/cursor
  ]
  # sandbox editor displays again, cursor is in editor
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊␣                                                .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  0   edit          copy            delete         .
    .                                                  add 2, 2                                         .
  ]
]

# page-down on sandbox side updates render-from to scroll sandboxes
after <global-keypress> [
  {
    break-unless sandbox-in-focus?
    page-down?:boolean <- equal k, 65518/page-down
    break-unless page-down?
    sandbox:address:sandbox-data <- get *env, sandbox:offset
    break-unless sandbox
    # slide down if possible
    {
      render-from:number <- get *env, render-from:offset
      number-of-sandboxes:number <- get *env, number-of-sandboxes:offset
      max:number <- subtract number-of-sandboxes, 1
      at-end?:boolean <- greater-or-equal render-from, max
      jump-if at-end?, +finish-event:label  # render nothing
      render-from <- add render-from, 1
      *env <- put *env, render-from:offset, render-from
    }
    hide-screen screen
    screen <- render-sandbox-side screen, env, render
    show-screen screen
    jump +finish-event:label
  }
]

# update-cursor takes render-from into account
after <update-cursor-special-cases> [
  {
    break-unless sandbox-in-focus?
    render-from:number <- get *env, render-from:offset
    scrolling?:boolean <- greater-or-equal render-from, 0
    break-unless scrolling?
    cursor-column:number <- get *current-sandbox, left:offset
    screen <- move-cursor screen, 2/row, cursor-column  # highlighted sandbox will always start at row 2
    return
  }
]

# 'page-up' on sandbox side is like 'page-down': updates render-from when necessary
after <global-keypress> [
  {
    break-unless sandbox-in-focus?
    page-up?:boolean <- equal k, 65519/page-up
    break-unless page-up?
    render-from:number <- get *env, render-from:offset
    at-beginning?:boolean <- equal render-from, -1
    break-if at-beginning?
    render-from <- subtract render-from, 1
    *env <- put *env, render-from:offset, render-from
    hide-screen screen
    screen <- render-sandbox-side screen, env, render
    show-screen screen
    jump +finish-event:label
  }
]

# sandbox belonging to 'env' whose next-sandbox is 'in'
# return 0 if there's no such sandbox, either because 'in' doesn't exist in 'env', or because it's the first sandbox
def previous-sandbox env:address:programming-environment-data, in:address:sandbox-data -> out:address:sandbox-data [
  local-scope
  load-ingredients
  curr:address:sandbox-data <- get *env, sandbox:offset
  return-unless curr, 0/nil
  next:address:sandbox-data <- get *curr, next-sandbox:offset
  {
    return-unless next, 0/nil
    found?:boolean <- equal next, in
    break-if found?
    curr <- copy next
    next <- get *curr, next-sandbox:offset
    loop
  }
  return curr
]

scenario scrolling-down-on-recipe-side [
  trace-until 100/app  # trace too long
  assume-screen 100/width, 10/height
  # initialize sandbox side and create a sandbox
  1:text <- new [ 
]
  # create a sandbox
  2:text <- new [add 2, 2]
  3:address:programming-environment-data <- new-programming-environment screen:address:screen, 1:text, 2:text
  render-all screen, 3:address:programming-environment-data, render
  assume-console [
    press F4
  ]
  event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  # hit 'down' in recipe editor
  assume-console [
    press page-down
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
    4:character/cursor <- copy 9251/    print screen:address:screen, 4:character/cursor
  ]
  # cursor moves down on recipe side
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                  .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊0   edit          copy            delete         .
    .                                                  add 2, 2                                         .
  ]
]

scenario scrolling-through-multiple-sandboxes [
  trace-until 100/app  # trace too long
  assume-screen 100/width, 10/height
  # initialize environment
  1:text <- new []
  2:text <- new []
  3:address:programming-environment-data <- new-programming-environment screen:address:screen, 1:text, 2:text
  render-all screen, 3:address:programming-environment-data, render
  # create 2 sandboxes
  assume-console [
    press ctrl-n
    type [add 2, 2]
    press F4
    type [add 1, 1]
    press F4
  ]
  event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  4:character/cursor <- copy 9251/  print screen:address:screen, 4:character/cursor
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊␣                                                .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  0   edit          copy            delete         .
    .                                                  add 1, 1                                         .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  1   edit          copy            delete         .
    .                                                  add 2, 2                                         .
    .                                                  4                                                .
  ]
  # hit 'page-down'
  assume-console [
    press page-down
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
    4:character/cursor <- copy 9251/    print screen:address:screen, 4:character/cursor
  ]
  # sandbox editor hidden; first sandbox displayed
  # cursor moves to first sandbox
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊␣   edit          copy            delete         .
    .                                                  add 1, 1                                         .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  1   edit          copy            delete         .
    .                                                  add 2, 2                                         .
    .                                                  4                                                .
  ]
  # hit 'page-down' again
  assume-console [
    press page-down
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  ]
  # just second sandbox displayed
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊1   edit          copy            delete         .
    .                                                  add 2, 2                                         .
    .                                                  4                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
  # hit 'page-down' again
  assume-console [
    press page-down
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  ]
  # no change
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊1   edit          copy            delete         .
    .                                                  add 2, 2                                         .
    .                                                  4                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
  # hit 'page-up'
  assume-console [
    press page-up
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  ]
  # back to displaying both sandboxes without editor
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊0   edit          copy            delete         .
    .                                                  add 1, 1                                         .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  1   edit          copy            delete         .
    .                                                  add 2, 2                                         .
    .                                                  4                                                .
  ]
  # hit 'page-up' again
  assume-console [
    press page-up
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
    4:character/cursor <- copy 9251/    print screen:address:screen, 4:character/cursor
  ]
  # back to displaying both sandboxes as well as editor
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊␣                                                .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  0   edit          copy            delete         .
    .                                                  add 1, 1                                         .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  1   edit          copy            delete         .
    .                                                  add 2, 2                                         .
    .                                                  4                                                .
  ]
  # hit 'page-up' again
  assume-console [
    press page-up
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
    4:character/cursor <- copy 9251/    print screen:address:screen, 4:character/cursor
  ]
  # no change
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊␣                                                .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  0   edit          copy            delete         .
    .                                                  add 1, 1                                         .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  1   edit          copy            delete         .
    .                                                  add 2, 2                                         .
    .                                                  4                                                .
  ]
]

scenario scrolling-manages-sandbox-index-correctly [
  trace-until 100/app  # trace too long
  assume-screen 100/width, 10/height
  # initialize environment
  1:text <- new []
  2:text <- new []
  3:address:programming-environment-data <- new-programming-environment screen:address:screen, 1:text, 2:text
  render-all screen, 3:address:programming-environment-data, render
  # create a sandbox
  assume-console [
    press ctrl-n
    type [add 1, 1]
    press F4
  ]
  event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  0   edit          copy            delete         .
    .                                                  add 1, 1                                         .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
  # hit 'page-down' and 'page-up' a couple of times. sandbox index should be stable
  assume-console [
    press page-down
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  ]
  # sandbox editor hidden; first sandbox displayed
  # cursor moves to first sandbox
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊0   edit          copy            delete         .
    .                                                  add 1, 1                                         .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
  # hit 'page-up' again
  assume-console [
    press page-up
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  ]
  # back to displaying both sandboxes as well as editor
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                                                                   .
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                  0   edit          copy            delete         .
    .                                                  add 1, 1                                         .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
  # hit 'page-down'
  assume-console [
    press page-down
  ]
  run [
    event-loop screen:address:screen, console:address:console, 3:address:programming-environment-data
  ]
  # sandbox editor hidden; first sandbox displayed
  # cursor moves to first sandbox
  screen-should-contain [
    .                                                                                 run (F4)           .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┊0   edit          copy            delete         .
    .                                                  add 1, 1                                         .
    .                                                  2                                                .
    .                                                  ┊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━.
    .                                                                                                   .
  ]
]