# Toy lisp interpreter
#
# To run:
#   $ ./ntranslate 0*.subx apps/subx-common.subx apps/mulisp.subx
#   $ ./a.elf
#   42
#   => 42
#   ^D
#   $

== code

Entry:  # run tests if necessary, a REPL if not
    # . prolog
    89/<- %ebp 4/r32/esp
    # initialize heap
    (new-segment Heap-size Heap)
    # if (argc <= 1) goto run-main
    81 7/subop/compare *ebp 1/imm32
    7e/jump-if-lesser-or-equal $run-main/disp8
    # if (argv[1] != "test")) goto run-main
    (kernel-string-equal? *(ebp+8) "test")  # => eax
    3d/compare-eax-and 0/imm32
    74/jump-if-equal $run-main/disp8
    #
    (run-tests)
    # syscall(exit, *Num-test-failures)
    8b/-> *Num-test-failures 3/r32/ebx
    eb/jump $main:end/disp8
$run-main:
    (repl Stdin Stdout)
    # syscall(exit, 0)
    bb/copy-to-ebx 0/imm32
$main:end:
    b8/copy-to-eax 1/imm32/exit
    cd/syscall 0x80/imm8

# type cell = nil | num | char | symbol | pair | array | stream
#     tag:    0     1     2       3       4       5       6
# numbers start with a digit and are always in hex
# characters start with a backslash
# pairs start with '('
# arrays start with '['
# symbols start with anything else but quote, backquote, unquote or splice

repl:  # in : (address buffered-file), out : (address buffered-file) -> <void>
    # . prolog
    55/push-ebp
    89/<- %ebp 4/r32/esp
    # . save registers
    50/push-eax
$repl:loop:
    (lisp-read Stdin)  # => eax : (address cell)
    # if (eax == 0) break
    3d/compare-eax-and 0/imm32
    74/jump-if-equal $repl:end/disp8
    #
    (lisp-eval %eax)  # => eax : (address cell)
    (lisp-print Stdout %eax)
    # loop
    eb/jump $repl:loop/disp8
$repl:end:
    # . restore registers
    58/pop-to-eax
    # . epilog
    89/<- %esp 5/r32/ebp
    5d/pop-to-ebp
    c3/return

lisp-read:  # in : (address buffered-file) -> eax : (address cell)
    # . prolog
    55/push-ebp
    89/<- %ebp 4/r32/esp
    # . save registers
    # var s/ecx : (address stream) = new-stream(512)
    81 5/subop/subtract %esp 0x200/imm32
    68/push 0x200/imm32/size
    68/push 0/imm32/read
    68/push 0/imm32/write
    89/<- %ecx 4/r32/esp
    #
    (clear-stream %ecx)
    (read-line-buffered *(ebp+8) %ecx)
    # if (s->write == 0) return null
    81 7/subop/compare *ecx 0/imm32
    75/jump-if-not-equal $lisp-read:loop/disp8
    b8/copy-to-eax 0/imm32/eof
    eb/jump $lisp-read:end/disp8
$lisp-read:loop:
    # return s
    89/<- %eax 1/r32/ecx
$lisp-read:end:
    # . reclaim locals
    81 0/subop/add %esp 0x20c/imm32
    # . restore registers
    # . epilog
    89/<- %esp 5/r32/ebp
    5d/pop-to-ebp
    c3/return

lisp-eval:  # in : (address cell) -> eax : (address cell)
    # . prolog
    55/push-ebp
    89/<- %ebp 4/r32/esp
    # . save registers
    8b/-> *(ebp+8) 0/r32/eax
$lisp-eval:end:
    # . restore registers
    # . epilog
    89/<- %esp 5/r32/ebp
    5d/pop-to-ebp
    c3/return

lisp-print:  # out : (address buffered-file), x : (address cell)
    # . prolog
    55/push-ebp
    89/<- %ebp 4/r32/esp
    # . save registers
    # write(x)
    (write-buffered Stdout "=> ")
    (write-stream-data Stdout *(ebp+0xc))
    (flush Stdout)
$lisp-print:end:
    # . restore registers
    # . epilog
    89/<- %esp 5/r32/ebp
    5d/pop-to-ebp
    c3/return

== data

Nil:
  0/imm32/tag
  0/imm32/data