# Copyright (C) 2007, Parrot Foundation. # $Id: pdd19_pir.pod 39568 2009-06-15 09:41:30Z barney $ =head1 PDD 19: Parrot Intermediate Representation (PIR) =head2 Version $Revision: 39568 $ =head2 Abstract This document outlines the architecture and core syntax of Parrot Intermediate Representation (PIR). =head2 Description PIR is a stable, middle-level language intended both as a target for the generated output from high-level language compilers, and for human use developing core features and extensions for Parrot. =head3 Basic Syntax A valid PIR program consists of a sequence of statements, directives, comments and empty lines. =head4 Statements A statement starts with an optional label, contains an instruction, and is terminated by a newline (<NL>). Each statement must be on its own line. [label:] [instruction] <NL> An instruction may be either a low-level opcode or a higher-level PIR operation, such as a subroutine call, a method call, a directive, or PIR syntactic sugar. =head4 Directives A directive provides information for the PIR compiler that is outside the normal flow of executable statements. Directives are all prefixed with a ".", as in C<.local> or C<.sub>. =head4 Comments Comments start with C<#> and last until the following newline. PIR also allows comments in Pod format. Comments, Pod content, and empty lines are ignored. =head4 Identifiers Identifiers start with a letter or underscore, then may contain additionally letters, digits, and underscores. Identifiers don't have any limit on length at the moment, but some sane-but-generous length limit may be imposed in the future (256 chars, 1024 chars?). The following examples are all valid identifiers. a _a A42 Opcode names are not reserved words in PIR, and may be used as variable names. For example, you can define a local variable named C<print>. [See RT #24251] Note that currently, by using an opcode name as a local variable name, the variable will I<hide> the opcode name, effectively making the opcode unusable. In the future this will be resolved. The PIR language is designed to have as few reserved keywords as possible. Currently, in contrast to opcode names, PIR keywords I<are> reserved, and cannot be used as identifiers. Some opcode names are, in fact, PIR keywords, which therefore cannot be used as identifiers. This, too, will be resolved in a future re-implementation of the PIR compiler. The following are PIR keywords, and cannot currently be used as identifiers: goto if int null num pmc string unless =head4 Labels A label declaration consists of a label name followed by a colon. A label name conforms to the standard requirements for identifiers. A label declaration may occur at the start of a statement, or stand alone on a line, but always within a subroutine. A reference to a label consists of only the label name, and is generally used as an argument to an instruction or directive. A PIR label is accessible only in the subroutine where it's defined. A label name must be unique within a subroutine, but it can be reused in other subroutines. =begin PIR_FRAGMENT goto label1 # ... label1: =end PIR_FRAGMENT =head4 Registers and Variables There are two ways of referencing Parrot's registers. The first is through named local variables declared with C<.local>. =begin PIR_FRAGMENT .local pmc foo =end PIR_FRAGMENT The type of a named variable can be C<int>, C<num>, C<string> or C<pmc>, corresponding to the types of registers. No other types are used. The second way of referencing a register is through a register variable C<$In>, C<$Sn>, C<$Nn>, or C<$Pn>. The capital letter indicates the type of the register (integer, string, number, or PMC). I<n> consists of digit(s) only. There is no limit on the size of I<n>. There is no direct correspondence between the value of I<n> and the position of the register in the register set, C<$P42> may be stored in the zeroth PMC register, if it is the only register in the subroutine. =head3 Constants Constants may be used in place of registers or variables. A constant is not allowed on the left side of an assignment, or in any other context where the variable would be modified. =over 4 =item 'single-quoted string constant' Are delimited by single-quotes (C<'>). They are taken to be ASCII encoded. No escape sequences are processed. =item "double-quoted string constants" Are delimited by double-quotes (C<">). A C<"> inside a string must be escaped by C<\>. The default encoding for a double-quoted string constant is 7-bit ASCII, other character sets and encodings must be marked explicitly using a charset or encoding flag. =item <<"heredoc", <<'heredoc' Heredocs work like single or double quoted strings. All lines up to the terminating delimiter are slurped into the string. The delimiter has to be on its own line, at the beginning of the line and with no trailing whitespace. Assignment of a heredoc: =begin PIR_FRAGMENT $S0 = <<"EOS" ... EOS =end PIR_FRAGMENT A heredoc as an argument: =begin PIR_FRAGMENT .local pmc function, arg # ... function(<<"END_OF_HERE", arg) ... END_OF_HERE .yield(<<'EOS') ... EOS .return(<<'EOS') ... EOS =end PIR_FRAGMENT Although currently not possible, a future implementation of the PIR language will allow you to use multiple heredocs within a single statement or directive: =begin PIR_FRAGMENT_TODO function(<<'INPUT', <<'OUTPUT', 'some test') ... INPUT ... OUTPUT =end PIR_FRAGMENT_TODO =item charset:"string constant" Like above with a character set attached to the string. Valid character sets are currently: C<ascii> (the default), C<binary>, C<unicode> (with UTF-8 as the default encoding), and C<iso-8859-1>. =back =head3 String escape sequences Inside double-quoted strings the following escape sequences are processed. \xhh 1..2 hex digits \ooo 1..3 oct digits \cX control char X \x{h..h} 1..8 hex digits \uhhhh 4 hex digits \Uhhhhhhhh 8 hex digits \a, \b, \t, \n, \v, \f, \r, \e, \\, \" =over 4 =item encoding:charset:"string constant" Like above with an extra encoding attached to the string. For example: set S0, utf8:unicode:"«" The encoding and charset are attached to the string constant, and adopted by any string container the constant is assigned to. The standard escape sequences are honored within strings with an alternate encoding, so in the example above, you can include a particular Unicode character as either a literal sequence of bytes, or as an escape sequence. =item numeric constants Both integers (C<42>) and numbers (C<3.14159>) may appear as constants. C<0x> and C<0b> denote hex and binary constants respectively. =back =head3 Directives =over 4 =item .local <type> <identifier> [:unique_reg] Define a local name I<identifier> within a subroutine with the given I<type>. You can define multiple identifiers of the same type by separating them with commas: .local int i, j The optional C<:unique_reg> modifier will force the register allocator to associate the identifier with a unique register for the duration of the subroutine. If the register allocator is thought of as an optimization tool for allowing fewer registers to be used in a register frame by reusing unused registers, then the C<:unique_reg> directive forces this optimization to be turned off. This can be important in a number of situations: =over 4 =item * When a subroutine has a small fixed number of registers =item * When a named variable or named register is used throughout the entire subroutine =item * When a reference needs to be made to a register =back =item .lex <string constant>, <reg> Declare a lexical variable that is an alias for a PMC register. For example, given this preamble: =begin PIR_FRAGMENT .lex '$a', $P0 $P1 = new 'Integer' =end PIR_FRAGMENT These two opcodes have an identical effect: =begin PIR_FRAGMENT $P0 = $P1 store_lex '$a', $P1 =end PIR_FRAGMENT And these two opcodes also have an identical effect: =begin PIR_FRAGMENT $P1 = $P0 $P1 = find_lex '$a' =end PIR_FRAGMENT =item .const <type> <identifier> = <const> Define a constant named I<identifier> of type I<type> and assign value I<const> to it. The I<type> must be C<int>, C<num>, C<string> or a string constant indicating the PMC type. This allows you to create PMC constants representing subroutines; the value of the constant in that case is the name of the subroutine. If the referred subroutine has an C<:immediate> modifier and it returns a value, then that value is stored instead of the subroutine. C<.const> declarations representing subroutines can only be written within a C<.sub>. The constant is stored in the constant table of the current bytecode file. =item .globalconst <type> <identifier> = <const> As C<.const> above, but the defined constant is globally accessible. C<.globalconst> may only be used within a C<.sub>. =item .sub .sub <identifier> [:<modifier> ...] .sub <quoted string> [:<modifier> ...] Define a subroutine. All code in a PIR source file must be defined in a subroutine. See the section L<Subroutine modifiers> for available modifiers. Optional modifiers are a list separated by spaces. The name of the sub may be either a bare identifier or a quoted string constant. Bare identifiers must be valid PIR identifiers (see L<Identifiers> above), but string sub names can contain any characters, including characters from different character sets (see L<Constants> above). Always paired with C<.end>. =item .end End a subroutine. Always paired with C<.sub>. =item .namespace [ <identifier> ; <identifier> ] .namespace [ <key>? ] key: <identifier> [';' <identifier>]* Defines the namespace from this point onwards. By default the program is not in any namespace. If you specify more than one, separated by semicolons, it creates nested namespaces, by storing the inner namespace object in the outer namespace's global pad. You can specify the root namespace by using empty brackets, such as: =begin PIR .namespace [ ] =end PIR The brackets are not optional, although the key inside them is. =item .loadlib 'lib_name' Load the given library at compile time, that is, as soon that line is parsed. See also the C<loadlib> opcode, which does the same at run time. A library loaded this way is also available at runtime, as if it has been loaded again in C<:load>, so there is no need to call C<loadlib> at runtime. =item .HLL <hll_name> Define the HLL namespace from that point on in the file. Takes one string constant, the name of the HLL. By default, the HLL namespace is 'parrot'. =item .line <integer> Set the current PIR line number to the value specified. This is useful in case the PIR code is generated from some source PIR files, and error messages should print the source file's line number, not the line number of the generated file. Note that line numbers increment per line of PIR; if you are trying to store High Level Language debug information, you should instead be using the C<.annotate> directive. =item .file <quoted_string> Set the current PIR file name to the value specified. This is useful in case the PIR code is generated from some source PIR files, and error messages should print the source file's name, not the name of the generated file. =item .annotate <key>, <value> Makes an entry in the bytecode annotations table. This is used to store high level language debug information. Examples: =begin PIR_FRAGMENT .annotate "file", "aardvark.p6" .annotate "line", 5 .annotate "column", 24 =end PIR_FRAGMENT An annotation stays in effect until the next annotation with the same key or the end of the current compilation unit (that is, if you use a tool such as C<pbc_merge> to link multiple bytecode files, then annotations will not spill over from one mergee's bytecode to another). One annotation covers many PIR instructions. If the result of compiling one line of HLL code is 15 lines of PIR, you only need to emit one annotation before the first of those 15 lines to set the line number. =begin PIR_FRAGMENT .annotate "line", 42 =end PIR_FRAGMENT The key must always be a quoted string. The value may be an integer, a number or a quoted string. Note that integer values are stored most compactly; should you instead of the above annotate directive emit: =begin PIR_FRAGMENT .annotate "line", "42" =end PIR_FRAGMENT then instead "42" is stored as a string, taking up more space in the resulting bytecode file. =back =head4 Subroutine modifiers =over 4 =item :main Define "main" entry point to start execution. If multiple subroutines are marked as B<:main>, the B<last> marked subroutine is used. Only the first file loaded or compiled counts; subs marked as B<:main> are ignored by the B<load_bytecode> op. If no B<:main> modifier is specified, execution starts at the first subroutine in the file. =item :load Run this subroutine when loaded by the B<load_bytecode> op (i.e. neither in the initial program file nor compiled from memory). This is complementary to what B<:init> does (below); to get both behaviours, use B<:init :load>. If multiple subs have the B<:load> pragma, the subs are run in source code order. =item :init Run the subroutine when the program is run directly (that is, not loaded as a module), including when it is compiled from memory. This is complementary to what B<:load> does (above); to get both behaviours, use B<:init :load>. =item :anon Do not install this subroutine in the namespace. Allows the subroutine name to be reused. =item :multi(type1, type2...) Engage in multiple dispatch with the listed types. See F<docs/pdds/pdd27_multi_dispatch.pod> for more information on the multiple dispatch system. =item :immediate Execute this subroutine immediately after being compiled, which is analogous to C<BEGIN> in Perl 5. In addition, if the sub returns a PMC value, that value replaces the sub in the constant table of the bytecode file. This makes it possible to build constants at compile time, provided that (a) the generated constant can be computed at compile time (i.e. doesn't depend on the runtime environment), and (b) the constant value is of a PMC class that supports saving in a bytecode file. {{ TODO: need a freeze/thaw reference }}. For instance, after compilation of the sub 'init', that sub is executed immediately (hence the C<:immediate> modifier). Instead of storing the sub 'init' in the constants table, the value returned by 'init' is stored, which in this example is a FixedIntegerArrray. =begin PIR .sub main :main .const "Sub" initsub = "init" .end .sub init :immediate .local pmc array array = new 'FixedIntegerArray' array = 256 # set size to 256 # code to initialize array .return (array) .end =end PIR =item :postcomp Execute immediately after being compiled, but only if the subroutine is in the initial file (i.e. not in PIR compiled as result of a C<load_bytecode> instruction from another file). As an example, suppose file C<main.pir> contains: =begin PIR .sub main load_bytecode 'foo.pir' .end =end PIR and the file C<foo.pir> contains: =begin PIR .sub foo :immediate print '42' .end .sub bar :postcomp print '43' .end =end PIR Executing C<foo.pir> will run both C<foo> and C<bar>. On the other hand, executing C<main.pir> will run only C<foo>. If C<foo.pir> is compiled to bytecode, only C<foo> will be run, and loading C<foo.pbc> will not run either C<foo> or C<bar>. =item :method =begin PIR .sub bar :method # ... .end .sub bar :method('foo') # ... .end =end PIR The marked C<.sub> is a method, added as a method in the class that corresponds to the current namespace, and not stored in the namespace. In the method body, the object PMC can be referred to with C<self>. If a string argument is given to C<:method> the method is stored with that name instead of the C<.sub> name. =item :vtable =begin PIR .sub bar :vtable # ... .end .sub bar :vtable('foo') # ... .end =end PIR The marked C<.sub> overrides a vtable function, and is not stored in the namespace. By default, it overrides a vtable function with the same name as the C<.sub> name. To override a different vtable function, use C<:vtable('...')>. For example, to have a C<.sub> named I<ToString> also be the vtable function C<get_string>), use C<:vtable('get_string')>. When the B<:vtable> modifier is set, the object PMC can be referred to with C<self>, as with the B<:method> modifier. =item :outer(subname) The marked C<.sub> is lexically nested within the sub known by I<subname>. =item :subid( <string_constant> ) Specifies a unique string identifier for the subroutine. This is useful for referring to a particular subroutine with C<:outer>, even though several subroutines in the file may have the same name (because they are multi, or in different namespaces). =item :instanceof( <string_constant> ) The C<:instanceof> pragma is an experimental pragma that creates a sub as a PMC type other than 'Sub'. However, as currently implemented it doesn't work well with C<:outer> or existing PMC types such as C<Closure>, C<Coroutine>, etc. =item :nsentry( <string_constant> ) Specify the name by which the subroutine is stored in the namespace. The default name by which a subroutine is stored in the namespace (if this modifier is missing), is the subroutine's name as given after the C<.sub> directive. This modifier allows to override this. =back =head4 Directives used for Parrot calling conventions. =over 4 =item .begin_call and .end_call Directives to start and end a subroutine invocation, respectively. =item .begin_return and .end_return Directives to start and end a statement to return values. =item .begin_yield and .end_yield Directives to start and end a statement to yield values. =item .call Takes either 2 arguments: the sub and the return continuation, or the sub only. For the latter case an B<invokecc> gets emitted. Providing an explicit return continuation is more efficient, if its created outside of a loop and the call is done inside a loop. =item .invocant Directive to specify the object for a method call. Use it in combination with C<.meth_call>. =item .meth_call Directive to do a method call. It calls the specified method on the object that was specified with the C<.invocant> directive. =item .nci_call Directive to make a call through the Native Calling Interface (NCI). The specified subroutine must be loaded using the <dlfunc> op that takes the library, function name and function signature as arguments. See F<docs/pdds/pdd16_native_call> for details. =item .set_return <var> [:<modifier>]* Between C<.begin_return> and C<.end_return>, specify one or more of the return value(s) of the current subroutine. Available modifiers: C<:flat>, C<:named>. =item .set_yield <var> [:<modifier>]* Between C<.begin_yield> and C<.end_yield>, specify one or more of the yield value(s) of the current subroutine. Available modifiers: C<:flat>, C<:named>. =item .set_arg <var> [:<modifier>]* Between C<.begin_call> and C<.call>, specify an argument to be passed. Available modifiers: C<:flat>, C<:named>. =item .get_result <var> [:<modifier>]* Between C<.call> and C<.end_call>, specify where one or more return value(s) should be stored. Available modifiers: C<:slurpy>, C<:named>, C<:optional>, and C<:opt_flag>. =back =head4 Directives for subroutine parameters =over 4 =item .param <type> <identifier> [:<modifier>]* At the top of a subroutine, declare a local variable, in the manner of C<.local>, into which parameter(s) of the current subroutine should be stored. Available modifiers: C<:slurpy>, C<:named>, C<:optional>, C<:opt_flag> and C<:unique_reg>. =back =head4 Parameter Passing and Getting Flags See L<PDD03|pdds/pdd03_calling_conventions.pod> for a description of the meaning of the flag bits C<SLURPY>, C<OPTIONAL>, C<OPT_FLAG>, and C<FLAT>, which correspond to the calling convention modifiers C<:slurpy>, C<:optional>, C<:opt_flag>, and C<:flat>. =head4 Catching Exceptions Using the C<push_eh> op you can install an exception handler. If an exception is thrown, Parrot will execute the installed exception handler. In order to retrieve the thrown exception, use the C<.get_results> directive. This directive always takes one argument: an exception object. =begin PIR_FRAGMENT push_eh handler # ... handler: .local pmc exception .get_results (exception) # ... =end PIR_FRAGMENT This is syntactic sugar for the C<get_results> op, but any modifiers set on the targets will be handled automatically by the PIR compiler. The C<.get_results> directive must be the first instruction of the exception handler; only declarations (.lex, .local) may come first. To resume execution after handling the exception, just invoke the continuation stored in the exception. =begin PIR_FRAGMENT .local pmc exception, continuation # ... .get_results(exception) # ... continuation = exception['resume'] continuation() # ... =end PIR_FRAGMENT See L<PDD23|pdds/pdd23_exceptions.pod> for accessing the various attributes of the exception object. =head3 Syntactic Sugar Any PASM opcode is a valid PIR instruction. In addition, PIR defines some syntactic shortcuts. These are provided for ease of use by humans producing and maintaining PIR code. =over 4 =item goto <identifier> C<branch> to I<identifier> (label or subroutine name). Examples: goto END =item if <var> goto <identifier> If I<var> evaluates as true, jump to the named I<identifier>. =item unless <var> goto <identifier> Unless I<var> evaluates as true, jump to the named I<identifier>. =item if null <var> goto <identifier> If I<var> evaluates as null, jump to the named I<identifier>. =item unless null <var> goto <identifier> Unless I<var> evaluates as null, jump to the named I<identifier>. =item if <var1> <relop> <var2> goto <identifier> The I<relop> can be: C<E<lt>, E<lt>=, ==, != E<gt>= E<gt>>. which translate to the PASM opcodes C<lt>, C<le>, C<eq>, C<ne>, C<ge> or C<gt>. If I<var1 relop var2> evaluates as true, jump to the named I<identifier>. =item unless <var1> <relop> <var2> goto <identifier> The I<relop> can be: C<E<lt>, E<lt>=, ==, != E<gt>= E<gt>>. Unless I<var1 relop var2> evaluates as true, jump to the named I<identifier>. =item <var1> = <var2> Assign a value. =item <var1> = <unary> <var2> Unary operations C<!> (NOT), C<-> (negation) and C<~> (bitwise NOT). =item <var1> = <var2> <binary> <var3> Binary arithmetic operations C<+> (addition), C<-> (subtraction), C<*> (multiplication), C</> (division), C<%> (modulus) and C<**> (exponent). Binary C<.> is concatenation and only valid for string arguments. C<E<lt>E<lt>> and C<E<gt>E<gt>> are arithmetic shifts left and right. C<E<gt>E<gt>E<gt>> is the logical shift right. Binary logic operations C<&&> (AND), C<||> (OR) and C<~~> (XOR). Binary bitwise operations C<&> (bitwise AND), C<|> (bitwise OR) and C<~> (bitwise XOR). Binary relational operations C<E<lt>, E<lt>=, ==, != E<gt>= E<gt>>. =item <var1> <op>= <var2> This is equivalent to C<E<lt>var1E<gt> = E<lt>var1E<gt> E<lt>opE<gt> E<lt>var2E<gt>>. Where I<op> is called an assignment operator and can be any of the following binary operators described earlier: C<+>, C<->, C<*>, C</>, C<%>, C<.>, C<&>, C<|>, C<~>, C<E<lt>E<lt>>, C<E<gt>E<gt>> or C<E<gt>E<gt>E<gt>>. =item <var> = <var> [ <var> ] A keyed C<set> operation for PMCs to retrieve a value from an aggregate. This maps to: set <var>, <var> [ <var> ] =item <var> [ <var> ] = <var> A keyed C<set> operation to set a value in an aggregate. This maps to: set <var> [ <var> ], <var> =item <var> = <opcode> <arguments> Many opcodes can use this PIR syntactic sugar. The first argument for the opcode is placed before the C<=>, and all remaining arguments go after the opcode name. For example: =begin PIR_FRAGMENT new $P0, 'Type' =end PIR_FRAGMENT becomes: =begin PIR_FRAGMENT $P0 = new 'Type' =end PIR_FRAGMENT Note that this only works for opcodes that have have a leading C<OUT> parameter. [this restriction unimplemented: RT #36283] =item ([<var1> [:<mod1> ...], ...]) = <var2>([<arg1> [:<mod2> ...], ...]) This is short for: .begin_call .set_arg <arg1> <modifier2> ... .call <var2> .get_result <var1> <modifier1> ... .end_call =item <var> = <var>([arg [:<modifier> ...], ...]) =item <var>([arg [:<modifier> ...], ...]) =item <var>."_method"([arg [:<modifier> ...], ...]) =item <var>.<var>([arg [:<modifier> ...], ...]) Function or method call. These notations are shorthand for a longer PCC function call. I<var> can denote a global subroutine, a local I<identifier> or a I<reg>. =item .return ([<var> [:<modifier> ...], ...]) Return from the current subroutine with zero or more values. =item .tailcall <var>(args) =item .tailcall <var>.'somemethod'(args) =item .tailcall <var>.<var>(args) Tail call: call a function or method and return from the sub with the function or method call return values. Internally, the call stack doesn't increase because of a tail call, so you can write recursive functions and not have stack overflows. Whitespace surrounding the dot ('.') that separates the object from the method is not allowed. =back =head3 Assignment and Morphing The C<=> syntactic sugar in PIR, when used in the simple case of: <var1> = <var2> directly corresponds to the C<set> opcode. So, two low-level arguments (int, num, or string registers, variables, or constants) are a direct C assignment, or a C-level conversion (int cast, float cast, a string copy, or a call to one of the conversion functions like C<string_to_num>). Assigning a PMC argument to a low-level argument calls the C<get_integer>, C<get_number>, or C<get_string> vtable function on the PMC. Assigning a low-level argument to a PMC argument calls the C<set_integer_native>, C<set_number_native>, or C<set_string_native> vtable function on the PMC (assign to value semantics). Two PMC arguments are a direct C assignment (assign to container semantics). For assign to value semantics for two PMC arguments use C<assign>, which calls the C<assign_pmc> vtable function. =head3 Macros This section describes the macro layer of the PIR language. The macro layer of the PIR compiler handles the following directives: =over 4 =item * C<.include> '<filename>' The C<.include> directive takes a string argument that contains the name of the PIR file that is included. The contents of the included file are inserted as if they were written at the point where the C<.include> directive occurs. The include file is searched for in the current directory and in runtime/parrot/include, in that order. The first file of that name to be found is included. The C<.include> directive's search order is subject to change. =item * C<.macro> <identifier> [<parameters>] The C<.macro> directive starts the a macro definition named by the specified identifier. The optional parameter list is a comma-separated list of identifiers, enclosed in parentheses. See C<.endm> for ending the macro definition. =item * C<.endm> Closes a macro definition. =item * C<.macro_const> <identifier> (<literal>|<reg>) =begin PIR .macro_const PI 3.14 =end PIR The C<.macro_const> directive is a special type of macro; it allows the user to use a symbolic name for a constant value. Like C<.macro>, the substitution occurs at compile time. It takes two arguments (not comma separated), the first is an identifier, the second a constant value or a register. =back The macro layer is completely implemented in the lexical analysis phase. The parser does not know anything about what happens in the lexical analysis phase. When the C<.include> directive is encountered, the specified file is opened and the following tokens that are requested by the parser are read from that file. A macro expansion is a dot-prefixed identifier. For instance, if a macro was defined as shown below: =begin PIR .macro foo(bar) # ... .endm =end PIR this macro can be expanded by writing C<.foo(42)>. The body of the macro will be inserted at the point where the macro expansion is written. A C<.macro_const> expansion is more or less the same as a C<.macro> expansion, except that a constant expansion cannot take any arguments, and the substitution of a C<.macro_const> contains no newlines, so it can be used within a line of code. =head4 Macro parameter list The parameter list for a macro is specified in parentheses after the name of the macro. Macro parameters are not typed. =begin PIR .macro foo(bar, baz, buz) # ... .endm =end PIR The number of arguments in the call to a macro must match the number of parameters in the macro's parameter list. Macros do not perform multidispatch, so you can't have two macros with the same name but different parameters. Calling a macro with the wrong number of arguments gives the user an error. If a macro defines no parameter list, parentheses are optional on both the definition and the call. This means that a macro defined as: =begin PIR .macro foo # ... .endm =end PIR can be expanded by writing either C<.foo> or C<.foo()>. And a macro definition written as: =begin PIR .macro foo() # ... .endm =end PIR can also be expanded by writing either C<.foo> or C<.foo()>. B<Note: IMCC requires you to write parentheses if the macro was declared with (empty) parentheses. Likewise, when no parentheses were written (implying an empty parameter list), no parentheses may be used in the expansion.> =over =item * Heredoc arguments Heredoc arguments are not allowed when expanding a macro. The next implementation of PIR ("PIRC") will be able to handle this correctly. This means that, currently, when using IMCC, the following is not allowed: =begin PIR_TODO .macro foo(bar) ... .endm .foo(<<'EOS') This is a heredoc string. EOS =end PIR_TODO Using braces, { }, allows you to span multiple lines for an argument. See runtime/parrot/include/hllmacros.pir for examples and possible usage. A simple example is this: =begin PIR .macro foo(a,b) .a .b .endm .sub main .foo({ print "1" print "2" }, { print "3" print "4" }) .end =end PIR This will expand the macro C<foo>, after which the input to the PIR parser is: =begin PIR .sub main print "1" print "2" print "3" print "4" .end =end PIR which will result in the output: 1234 =back =head4 Unique local labels Within the macro body, the user can declare a unique label identifier using the value of a macro parameter, like so: =begin PIR .macro foo(a) # ... .label $a: # ... .endm =end PIR =head4 Unique local variables B<Note: this is not yet implemented in IMCC>. Within the macro body, the user can declare a local variable with a unique name. =begin PIR .macro foo() # ... .macro_local int b # ... .b = 42 print .b # prints the value of the unique variable (42) # ... .endm =end PIR The C<.macro_local> directive declares a local variable with a unique name in the macro. When the macro C<.foo()> is called, the resulting code that is given to the parser will read as follows: =begin PIR .sub main .local int local__foo__b__2 # ... local__foo__b__2 = 42 print local__foo__b__2 .end =end PIR The user can also declare a local variable with a unique name set to the symbolic value of one of the macro parameters. =begin PIR .macro foo(b) # ... .macro_local int $b # ... .$b = 42 print .$b # prints the value of the unique variable (42) print .b # prints the value of parameter "b", which is # also the name of the variable. # ... .endm =end PIR So, the special C<$> character indicates whether the symbol is interpreted as just the value of the parameter, or that the variable by that name is meant. Obviously, the value of C<b> should be a string. The automatic name munging on C<.macro_local> variables allows for using multiple macros, like so: =begin PIR_TODO .macro foo(a) .macro_local int $a .endm .macro bar(b) .macro_local int $b .endm .sub main .foo("x") .bar("x") .end =end PIR_TODO This will result in code for the parser as follows: =begin PIR .sub main .local int local__foo__x__2 .local int local__bar__x__4 .end =end PIR Each expansion is associated with a unique number; for labels declared with C<.macro_label> and locals declared with C<.macro_local> expansions, this means that multiple expansions of a macro will not result in conflicting label or local names. =head4 Ordinary local variables Defining a non-unique variable can still be done, using the normal syntax: =begin PIR .macro foo(b) .local int b .macro_local int $b .endm =end PIR When invoking the macro C<foo> as follows: =begin PIR_FRAGMENT .macro foo(b) #... .endm .foo("x") =end PIR_FRAGMENT there will be two variables: C<b> and C<x>. When the macro is invoked twice: =begin PIR_TODO .sub main .foo("x") .foo("y") .end =end PIR_TODO the resulting code that is given to the parser will read as follows: =begin PIR .sub main .local int b .local int local__foo__x .local int b .local int local__foo__y .end =end PIR Obviously, this will result in an error, as the variable C<b> is defined twice. If you intend the macro to create unique variables names, use C<.macro_local> instead of C<.local> to take advantage of the name munging. =head2 Examples =head3 Subroutine Definition A simple subroutine, marked with C<:main>, indicating it's the entry point in the file. Other sub modifiers include C<:load>, C<:init>, etc. =begin PIR .sub sub_label :main .param int a .param int b .param int c # ... .local pmc xy .return(xy) .end =end PIR =head3 Subroutine Call Invocation of a subroutine. In this case a continuation subroutine is created. =begin PIR_FRAGMENT .const "Sub" $P0 = "sub_label" $P1 = new 'Continuation' set_addr $P1, ret_addr # ... .local int x .local num y .local string z .begin_call .set_arg x .set_arg y .set_arg z .call $P0, $P1 # r = _sub_label(x, y, z) ret_addr: .local int r # optional - new result var .get_result r .end_call =end PIR_FRAGMENT =head3 NCI Call =begin PIR_FRAGMENT_TODO load_lib $P0, "libname" dlfunc $P1, $P0, "funcname", "signature" # ... .begin_call .set_arg x .set_arg y .set_arg z .nci_call $P1 # r = funcname(x, y, z) .local int r # optional - new result var .get_result r .end_call =end PIR_FRAGMENT_TODO =head3 Subroutine Call Syntactic Sugar Below there are three different ways to invoke the subroutine C<sub_label>. The first retrieves a single return value, the second retrieves 3 return values, whereas the last discards any return values. =begin PIR_FRAGMENT .local int r0, r1, r2 r0 = sub_label($I0, $I1, $I2) (r0, r1, r2) = sub_label($I0, $I1, $I2) sub_label($I0, $I1, $I2) =end PIR_FRAGMENT This also works for NCI calls, as the subroutine PMC will be a NCI sub, and on invocation will do the Right Thing. Instead of the label a subroutine object can be used too: =begin PIR_FRAGMENT_TODO get_global $P0, "sub_label" $P0(args) =end PIR_FRAGMENT_TODO =head3 Methods =begin PIR_TODO .namespace [ "Foo" ] .sub _sub_label :method [,Subpragma, ...] .param int a .param int b .param int c # ... self."_other_meth"() # ... .begin_return .set_return xy .end_return ... .end =end PIR_TODO The variable "self" automatically refers to the invocating object, if the subroutine declaration contains "method". =head3 Calling Methods The syntax is very similar to subroutine calls. The call is done with C<.meth_call> which must immediately be preceded by the C<.invocant>: =begin PIR_FRAGMENT_TODO .local int x, y, z .local pmc class, obj newclass class, "Foo" new obj, class .begin_call .set_arg x .set_arg y .set_arg z .invocant obj .meth_call "method" [, $P1 ] # r = obj."method"(x, y, z) .local int r # optional - new result var .get_result r .end_call ... =end PIR_FRAGMENT_TODO The return continuation is optional. The method can be a string constant or a string variable. =head3 Returning and Yielding .return ( a, b ) # return the values of a and b .return () # return no value .tailcall func_call() # tail call function .tailcall o."meth"() # tail method call Similarly, one can yield using the .yield directive .yield ( a, b ) # yield with the values of a and b .yield () # yield with no value =head2 Implementation There are multiple implementations of PIR, each of which will meet this specification for the syntax. Currently there are the following implementations: =over 4 =item * compilers/imcc This is the current implementation being used in Parrot. Some of the specified syntactic constructs in this PDD are not implemented in IMCC; these constructs are marked with notes saying so. =item * compilers/pirc This is a new implementation which will fix several of IMCC's shortcomings. It will replace IMCC. =item * languages/PIR This is a PGE-based implementation, but needs to be updated and completed. =back =head2 Attachments N/A =head2 Footnotes N/A =head2 References N/A =cut __END__ Local Variables: fill-column:78 End: