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diff --git a/nimdoc/rst2html/source/rst_examples.rst b/nimdoc/rst2html/source/rst_examples.rst new file mode 100644 index 000000000..7fa20de6c --- /dev/null +++ b/nimdoc/rst2html/source/rst_examples.rst @@ -0,0 +1,514 @@ +================ +Not a Nim Manual +================ + +:Authors: Andreas Rumpf, Zahary Karadjov +:Version: |nimversion| + +.. role:: nim(code) + :language: nim +.. default-role:: nim + +.. contents:: + + + "Complexity" seems to be a lot like "energy": you can transfer it from the + end-user to one/some of the other players, but the total amount seems to remain + pretty much constant for a given task. -- Ran + + +About this document +=================== + +**Note**: This document is a draft! Several of Nim's features may need more +precise wording. This manual is constantly evolving into a proper specification. + +**Note**: The experimental features of Nim are +covered `here <manual_experimental.html>`_. + +**Note**: Assignments, moves, and destruction are specified in +the `destructors <destructors.html>`_ document. + +The language constructs are explained using an extended BNF, in which ``(a)*`` +means 0 or more ``a``'s, ``a+`` means 1 or more ``a``'s, and ``(a)?`` means an +optional *a*. Parentheses may be used to group elements. + +``&`` is the lookahead operator; ``&a`` means that an ``a`` is expected but +not consumed. It will be consumed in the following rule. + +Non-terminals start with a lowercase letter, abstract terminal symbols are in +UPPERCASE. Verbatim terminal symbols (including keywords) are quoted +with ``'``. An example:: + + ifStmt = 'if' expr ':' stmts ('elif' expr ':' stmts)* ('else' stmts)? + +In a typical Nim program, most of the code is compiled into the executable. +However, some of the code may be executed at +`compile-time`:idx:. This can include constant expressions, macro definitions, +and Nim procedures used by macro definitions. Most of the Nim language is +supported at compile-time, but there are some restrictions -- see `Restrictions +on Compile-Time Execution <#restrictions-on-compileminustime-execution>`_ for +details. We use the term `runtime`:idx: to cover both compile-time execution +and code execution in the executable. + +.. code-block:: nim + var a: array[0..1, char] + let i = 5 + try: + a[i] = 'N' + except IndexDefect: + echo "invalid index" + +Encoding +-------- + +All Nim source files are in the UTF-8 encoding (or its ASCII subset). Other +encodings are not supported. Any of the standard platform line termination +sequences can be used - the Unix form using ASCII LF (linefeed), the Windows +form using the ASCII sequence CR LF (return followed by linefeed), or the old +Macintosh form using the ASCII CR (return) character. All of these forms can be +used equally, regardless of the platform. + + +Indentation +----------- + +Nim's standard grammar describes an `indentation sensitive`:idx: language. +This means that all the control structures are recognized by indentation. +Indentation consists only of spaces; tabulators are not allowed. + +With this notation we can now easily define the core of the grammar: A block of +statements (simplified example):: + + ifStmt = 'if' expr ':' stmt + (IND{=} 'elif' expr ':' stmt)* + (IND{=} 'else' ':' stmt)? + + simpleStmt = ifStmt / ... + + stmt = IND{>} stmt ^+ IND{=} DED # list of statements + / simpleStmt # or a simple statement + + +String literals can be delimited by matching double quotes, and can +contain the following `escape sequences`:idx:\ : + +================== =================================================== + Escape sequence Meaning +================== =================================================== + ``\p`` platform specific newline: CRLF on Windows, + LF on Unix + ``\r``, ``\c`` `carriage return`:idx: + ``\n``, ``\l`` `line feed`:idx: (often called `newline`:idx:) + ``\f`` `form feed`:idx: + ``\t`` `tabulator`:idx: + ``\v`` `vertical tabulator`:idx: + ``\\`` `backslash`:idx: + ``\"`` `quotation mark`:idx: + ``\'`` `apostrophe`:idx: + ``\`` '0'..'9'+ `character with decimal value d`:idx:; + all decimal digits directly + following are used for the character + ``\a`` `alert`:idx: + ``\b`` `backspace`:idx: + ``\e`` `escape`:idx: `[ESC]`:idx: + ``\x`` HH `character with hex value HH`:idx:; + exactly two hex digits are allowed + ``\u`` HHHH `unicode codepoint with hex value HHHH`:idx:; + exactly four hex digits are allowed + ``\u`` {H+} `unicode codepoint`:idx:; + all hex digits enclosed in ``{}`` are used for + the codepoint +================== =================================================== + +.. code-block:: nim + """"long string within quotes"""" + +Produces:: + + "long string within quotes" + +Operators +--------- + +Nim allows user defined operators. An operator is any combination of the +following characters:: + + = + - * / < > + @ $ ~ & % | + ! ? ^ . : \ + +(The grammar uses the terminal OPR to refer to operator symbols as +defined here.) + +The following strings denote other tokens:: + + ` ( ) { } [ ] , ; [. .] {. .} (. .) [: + + +Otherwise, precedence is determined by the first character. + +================ ======================================================= ================== =============== +Precedence level Operators First character Terminal symbol +================ ======================================================= ================== =============== + 10 (highest) ``$ ^`` OP10 + 9 ``* / div mod shl shr %`` ``* % \ /`` OP9 + 8 ``+ -`` ``+ - ~ |`` OP8 + 7 ``&`` ``&`` OP7 + 6 ``..`` ``.`` OP6 + 5 ``== <= < >= > != in notin is isnot not of as from`` ``= < > !`` OP5 + 4 ``and`` OP4 + 3 ``or xor`` OP3 + 2 ``@ : ?`` OP2 + 1 *assignment operator* (like ``+=``, ``*=``) OP1 + 0 (lowest) *arrow like operator* (like ``->``, ``=>``) OP0 +================ ======================================================= ================== =============== + + +Constants and Constant Expressions +================================== + +A `constant`:idx: is a symbol that is bound to the value of a constant +expression. Constant expressions are restricted to depend only on the following +categories of values and operations, because these are either built into the +language or declared and evaluated before semantic analysis of the constant +expression: + +* literals +* built-in operators +* previously declared constants and compile-time variables +* previously declared macros and templates +* previously declared procedures that have no side effects beyond + possibly modifying compile-time variables + +These integer types are pre-defined: + +``int`` + the generic signed integer type; its size is platform-dependent and has the + same size as a pointer. This type should be used in general. An integer + literal that has no type suffix is of this type if it is in the range + ``low(int32)..high(int32)`` otherwise the literal's type is ``int64``. + +intXX + additional signed integer types of XX bits use this naming scheme + (example: int16 is a 16-bit wide integer). + The current implementation supports ``int8``, ``int16``, ``int32``, ``int64``. + Literals of these types have the suffix 'iXX. + +``uint`` + the generic `unsigned integer`:idx: type; its size is platform-dependent and has the same size as a pointer. An integer literal with the type suffix ``'u`` is of this type. + +Let ``T``'s be ``p``'s return type. NRVO applies for ``T`` +if ``sizeof(T) >= N`` (where ``N`` is implementation dependent), +in other words, it applies for "big" structures. + +Apart from built-in operations like array indexing, memory allocation, etc. +the ``raise`` statement is the only way to raise an exception. + +.. XXX document this better! + +`typedesc` used as a parameter type also introduces an implicit +generic. `typedesc` has its own set of rules: + +The ``!=``, ``>``, ``>=``, ``in``, ``notin``, ``isnot`` operators are in fact +templates: + +| ``a > b`` is transformed into ``b < a``. +| ``a in b`` is transformed into ``contains(b, a)``. +| ``notin`` and ``isnot`` have the obvious meanings. + +A template where every parameter is ``untyped`` is called an `immediate`:idx: +template. For historical reasons templates can be explicitly annotated with +an ``immediate`` pragma and then these templates do not take part in +overloading resolution and the parameters' types are *ignored* by the +compiler. Explicit immediate templates are now deprecated. + + + +Symbol lookup in generics +------------------------- + +Open and Closed symbols +~~~~~~~~~~~~~~~~~~~~~~~ + +The symbol binding rules in generics are slightly subtle: There are "open" and +"closed" symbols. A "closed" symbol cannot be re-bound in the instantiation +context, an "open" symbol can. Per default overloaded symbols are open +and every other symbol is closed. + +In templates identifiers can be constructed with the backticks notation: + +.. code-block:: nim + :test: "nim c $1" + + template typedef(name: untyped, typ: typedesc) = + type + `T name`* {.inject.} = typ + `P name`* {.inject.} = ref `T name` + + typedef(myint, int) + var x: PMyInt + +In the example ``name`` is instantiated with ``myint``, so \`T name\` becomes +``Tmyint``. + +Only top-level symbols that are marked with an asterisk (``*``) are +exported. + +The algorithm for compiling modules is: + +- compile the whole module as usual, following import statements recursively + +- if there is a cycle only import the already parsed symbols (that are + exported); if an unknown identifier occurs then abort + + +Collective imports from a directory +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The syntax ``import dir / [moduleA, moduleB]`` can be used to import multiple modules +from the same directory. + + +Pragmas +======= + +Pragmas are Nim's method to give the compiler additional information / +commands without introducing a massive number of new keywords. Pragmas are +processed on the fly during semantic checking. Pragmas are enclosed in the +special ``{.`` and ``.}`` curly brackets. Pragmas are also often used as a +first implementation to play with a language feature before a nicer syntax +to access the feature becomes available. + + +deprecated pragma +----------------- + +The deprecated pragma is used to mark a symbol as deprecated: + +**Note**: `c2nim <https://github.com/nim-lang/c2nim/blob/master/doc/c2nim.rst>`_ can parse a large subset of C++ and knows +about the ``importcpp`` pragma pattern language. It is not necessary +to know all the details described here. + + + +Pure libraries do not depend on any external ``*.dll`` or ``lib*.so`` binary +while impure libraries do. A wrapper is an impure library that is a very +low-level interface to a C library. + + +Pure libraries +============== + +Automatic imports +----------------- + +* `system <system.html>`_ + Basic procs and operators that every program needs. It also provides IO + facilities for reading and writing text and binary files. It is imported + implicitly by the compiler. Do not import it directly. It relies on compiler + magic to work. + +* `threads <threads.html>`_ + Basic Nim thread support. **Note**: This is part of the system module. Do not + import it explicitly. Enabled with ``--threads:on``. + +Code reordering +=============== + +The code reordering feature can implicitly rearrange procedure, template, and +macro definitions along with variable declarations and initializations at the top +level scope so that, to a large extent, a programmer should not have to worry +about ordering definitions correctly or be forced to use forward declarations to +preface definitions inside a module. + +.. + NOTE: The following was documentation for the code reordering precursor, + which was {.noForward.}. + + In this mode, procedure definitions may appear out of order and the compiler + will postpone their semantic analysis and compilation until it actually needs + to generate code using the definitions. In this regard, this mode is similar + to the modus operandi of dynamic scripting languages, where the function + calls are not resolved until the code is executed. Here is the detailed + algorithm taken by the compiler: + + 1. When a callable symbol is first encountered, the compiler will only note + the symbol callable name and it will add it to the appropriate overload set + in the current scope. At this step, it won't try to resolve any of the type + expressions used in the signature of the symbol (so they can refer to other + not yet defined symbols). + + 2. When a top level call is encountered (usually at the very end of the + module), the compiler will try to determine the actual types of all of the + symbols in the matching overload set. This is a potentially recursive process + as the signatures of the symbols may include other call expressions, whose + types will be resolved at this point too. + + 3. Finally, after the best overload is picked, the compiler will start + compiling the body of the respective symbol. This in turn will lead the + compiler to discover more call expressions that need to be resolved and steps + 2 and 3 will be repeated as necessary. + + Please note that if a callable symbol is never used in this scenario, its + body will never be compiled. This is the default behavior leading to best + compilation times, but if exhaustive compilation of all definitions is + required, using ``nim check`` provides this option as well. + +Example: + +.. code-block:: nim + + {.experimental: "codeReordering".} + + proc foo(x: int) = + bar(x) + + proc bar(x: int) = + echo(x) + + foo(10) + + +.. + TODO: Let's table this for now. This is an *experimental feature* and so the + specific manner in which ``declared`` operates with it can be decided in + eventuality, because right now it works a bit weirdly. + + The values of expressions involving ``declared`` are decided *before* the + code reordering process, and not after. As an example, the output of this + code is the same as it would be with code reordering disabled. + + .. code-block:: nim + {.experimental: "codeReordering".} + + proc x() = + echo(declared(foo)) + + var foo = 4 + + x() # "false" + +It is important to note that reordering *only* works for symbols at top level +scope. Therefore, the following will *fail to compile:* + + +Parameter constraints +--------------------- + +The `parameter constraint`:idx: expression can use the operators ``|`` (or), +``&`` (and) and ``~`` (not) and the following predicates: + + +The ``~`` operator +~~~~~~~~~~~~~~~~~~ + +The ``~`` operator is the **not** operator in patterns: + + +The ``**`` operator +~~~~~~~~~~~~~~~~~~~ + +The ``**`` is much like the ``*`` operator, except that it gathers not only +all the arguments, but also the matched operators in reverse polish notation: + +Nim significantly improves on the safety of these features via additional +pragmas: + +1) A `guard`:idx: annotation is introduced to prevent data races. +2) Every access of a guarded memory location needs to happen in an + appropriate `locks`:idx: statement. +3) Locks and routines can be annotated with `lock levels`:idx: to allow + potential deadlocks to be detected during semantic analysis. + +1. Two output parameters should never be aliased. +2. An input and an output parameter should not be aliased. +3. An output parameter should never be aliased with a global or thread local + variable referenced by the called proc. +4. An input parameter should not be aliased with a global or thread local + variable updated by the called proc. + +One problem with rules 3 and 4 is that they affect specific global or thread +local variables, but Nim's effect tracking only tracks "uses no global variable" +via ``.noSideEffect``. The rules 3 and 4 can also be approximated by a different rule: + +5. A global or thread local variable (or a location derived from such a location) + can only passed to a parameter of a ``.noSideEffect`` proc. + +These two procs are the two modus operandi of the real-time garbage collector: + +(1) GC_SetMaxPause Mode + + You can call ``GC_SetMaxPause`` at program startup and then each triggered + garbage collector run tries to not take longer than ``maxPause`` time. However, it is + possible (and common) that the work is nevertheless not evenly distributed + as each call to ``new`` can trigger the garbage collector and thus take ``maxPause`` + time. + +(2) GC_step Mode + + This allows the garbage collector to perform some work for up to ``us`` time. + This is useful to call in the main loop to ensure the garbage collector can do its work. + To bind all garbage collector activity to a ``GC_step`` call, + deactivate the garbage collector with ``GC_disable`` at program startup. + If ``strongAdvice`` is set to ``true``, + then the garbage collector will be forced to perform the collection cycle. + Otherwise, the garbage collector may decide not to do anything, + if there is not much garbage to collect. + You may also specify the current stack size via ``stackSize`` parameter. + It can improve performance when you know that there are no unique Nim references + below a certain point on the stack. Make sure the size you specify is greater + than the potential worst-case size. + + It can improve performance when you know that there are no unique Nim + references below a certain point on the stack. Make sure the size you specify + is greater than the potential worst-case size. + +These procs provide a "best effort" real-time guarantee; in particular the +cycle collector is not aware of deadlines. Deactivate it to get more +predictable real-time behaviour. Tests show that a 1ms max pause +time will be met in almost all cases on modern CPUs (with the cycle collector +disabled). + +Time measurement with garbage collectors +---------------------------------------- + +The garbage collectors' way of measuring time uses +(see ``lib/system/timers.nim`` for the implementation): + +1) ``QueryPerformanceCounter`` and ``QueryPerformanceFrequency`` on Windows. +2) ``mach_absolute_time`` on Mac OS X. +3) ``gettimeofday`` on Posix systems. + +As such it supports a resolution of nanoseconds internally; however, the API +uses microseconds for convenience. + +Introduction +============ + +.. raw:: html + <blockquote><p> + "Der Mensch ist doch ein Augentier -- schöne Dinge wünsch ich mir." + </p></blockquote> + + +This document is a tutorial for the programming language *Nim*. +This tutorial assumes that you are familiar with basic programming concepts +like variables, types, or statements but is kept very basic. The `manual +<manual.html>`_ contains many more examples of the advanced language features. +All code examples in this tutorial, as well as the ones found in the rest of +Nim's documentation, follow the `Nim style guide <nep1.html>`_. + +However, this does not work. The problem is that the procedure should not +only ``return``, but return and **continue** after an iteration has +finished. This *return and continue* is called a `yield` statement. Now +the only thing left to do is to replace the ``proc`` keyword by ``iterator`` +and here it is - our first iterator: + +| A1 header | A2 \| not fooled +| :--- | ----: | +| C1 | C2 **bold** | ignored | +| D1 `code \|` | D2 | also ignored +| E1 \| text | +| | F2 without pipe +not in table |