# Copyright (C) 2001-2005, The Perl Foundation.
# $Id: syntax.pod 12839 2006-05-30 14:34:31Z coke $

=head1 NAME

IMCC - syntax

=head1 VERSION

=over 4

=item 0.1 initial

=back

=head1 OVERVIEW

This document describes the IMCC syntax.

=head1 DESCRIPTION

=head1 Comments and empty lines

Comments start with B<#> and last until the following newline. These
and empty lines are ignored.

=head1 Statements

A valid imcc program consists of a sequence of I<statements>. A
I<statement> is terminated by a newline (<NL>).

=head2 General statement format

  [label:] [instruction] <NL>

=head2 Labels

Optional label for the given instruction, can stand on its own line.
Global labels start with an underscore, local labels shouldn't. A label must
conform to the syntax of B<identifier> described below.

=head1 INSTRUCTIONS

=head2 Terms used here

=over 4

=item <identifier>

Start with a letter or underscore, then may contain additionally
digits and B<::>.

Example:

    a
    _a
    A42
    a::b_c

=item <type>

B<int>, B<float>, B<string>, B<pmc> or a valid parrot PMC type like
B<Array>.

=item <reg>

A PASM register In, Sn, Nn, Pn, or a IMCC temporary
register $In, $Sn, $Nn, $Pn, where B<n> consists of digit(s) only.

=item <var>

A local B<identifier> or a B<reg> or a constant (when allowed).

=back

=head2 Constants

=over 4

=item 'char constant'

Are delimited by B<'>. They are taken to be C<ascii> encoded. No escape
sequences are processed.

=item "string constants"

Are delimited by B<">. A B<"> inside a string must be escaped by
B<\">.  Only 7-bit ASCII is accepted in string constants; to use
characters outside thar range, specify an encoding in the way below.

=item <<"heredoc",  <<'heredoc'

Heredocs work like single or double quoted strings. All lines up to
the terminating delimiter is slurped into the string. The delimiter
has to be on its own line with no trailing whitespace.

  $S0 = <<'EOT'
  ...
 EOT

  function(<<"END_OF_HERE", arg)
  ...
 END_OF_HERE

Only one heredoc can be active per statement line.

=item charset:"string constant"

Like above with a chracter 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

=head2 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 eample:

  set S0, utf8:unicode:"«"

The encoding and charset gets attaced to the string, no further processing
is done, specifically escape sequences are not honored.

=item numeric constants

B<0x> and B<0b> denote hex and binary constants.

=back

=head2 Directive instructions

=over 4

=item .pragma n_operators

Convert arithmethic infix operators to n_infix operations. The unary opcodes
C<abs>, C<not>, C<bnot>, C<bnots>, and C<neg> are also changed to use a B<n_>
prefix.

 .pragma n_operators 1
 .sub foo
   ...
   $P0 = $P1 + $P2           # n_add $P0, $P1, $P2
   $P2 = abs $P0             # n_abs $P2, $P0


=item .HLL "hll_name", "hll_lib"

Define the HLL for the current file. If the string C<hll_lib> isn't empty
this B<compile time pragma> also loads the shared lib for the HLL, so that
integer type constants are working for creating new PMCs.

=item .HLL_map .CoreType, .UserType

Whenever Parrot has to create PMCs inside C code on behalf of the running user
program it consults the current type mapping for the executing HLL and creates
a PMC of type I<.UserType> instead of I<.CoreType>, if such a mapping is defined.

E.g. with this code snippet ...

  .sub _my_init :immediate
    $P0 = loadlib 'dynlexpad'
  .end

  .HLL "Foo", ""
  .HLL_map .LexPad, .DynLexPad

  .sub main :main
    ...

... all subroutines for language I<Foo> would use a dynamic lexpad pmc.

=item .sub <identifier>

=item .end

Define a I<compilation unit> with the label B<identifier:>.

=item .emit

=item .eom

Define a I<compilation unit> containing PASM code.

=item .local <type> <identifier> [:unique_reg]

=item .sym <type> <identifier> [:unique_reg]

Define a local name B<identifier> for this I<compilation unit> and of the
given B<type>. You can define multiple identifiers of the same type by
separating them with commas:

  .sym 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
compilation unit.

=item .lex <identifier>, <reg>

Declare a lexical variable that is an alias for a PMC register. The
PIR compiler calls this method in response to a .lex STRING, PREG
directive. For example, given this preamble:

    .lex "$a", $P0
    $P1 = new Integer

    These two opcodes have an identical effect:

    $P0 = $P1
    store_lex "$a", $P1

    And these two opcodes also have an identical effect:

    $P1 = $P0
    $P1 = find_lex "$a"

=item .const <type> <identifier> = <const>

Define a named constant of style I<type> and value I<const>.

=item .namespace <identifier>

Open a new scope block. This "namespace" is not the same as the
.namespace [ <identifier> ] syntax, which is used for storing subroutines
in a particular namespace in the global symboltable.
This directive is useful in cases such as (pseudocode):

  local x = 1;
  print(x);       # prints 1
  do              # open a new namespace/scope block
    local x = 2;  # this x hides the previous x
    print(x);     # prints 2
  end             # close the current namespace
  print(x);       # prints 1 again

All types of common language constructs such as if, for, while, repeat and such
that have nested scopes, can use this directive.

=item .endnamespace <identifier>

Closes the scope block that was opened with .namespace <identifier>.

=item .namespace [ <identifier> ]

=item .namespace [ <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 with a C<\0>
prefix in the outer namespace's global pad.

=item .pcc_*

Directives used for Parrot Calling Conventions.

=back

=head2 Directives for subroutine parameters and return

=over 4

=item .param <type> <identifier> [:<flag> ...]

At the top of a subroutine, declare a local variable, in the mannter
of B<.local>, into which parameter(s) of the current subroutine should
be stored. Available flags:
C<:slurpy>, C<:optional>, C<:opt_flag> and C<:unique_reg>.

=item .param <reg> [:<flag> ...]

At the top of a subroutine, specify where parameter(s) of the current
subroutine should be stored.  Available flags:
C<:slurpy>, C<:optional>, C<:opt_flag> and C<:unique_reg>.

=item .return <var> [:<flag> ...]

Between B<.pcc_begin_return> and B<.pcc_end_return>, specify one or
more of the return value(s) of the current subroutine.  Available
flags:
C<:flat>.

=back

=head2 Directives for making a PCC call

=over 4

=item .arg <var> [:<flag> ...]

Between B<.pcc_begin> and B<.pcc_call>, specify an argument to be
passed.  Available flags:
C<:flat>.

=item .result <var> [:<flag> ...]

Between B<.pcc_call> and B<.pcc_end>, specify where one or more return
value(s) should be stored.  Available flags:
C<:slurpy>, C<:optional>, and C<:opt_count>.

=back

=head2 Parameter Passing Flags

See L<PDD03|pdds/pdd03_calling_conventions.pod> for a description of
the meaning of the flag bits bits C<SLURPY>, C<OPTIONAL>, C<OPT_FLAG>,
and C<FLAT>, which correspond to the claling convention flags
C<:slurpy>, C<:optional>, C<:opt_flag>, and C<:flat>.

[TODO - once these flag bits are solidified by long-term use, then we
may choose to copy appropriate bits of the documentation to here.]

=head2 Instructions

Instructions may be a valid PASM instruction or anything listed here
below:

=over 4

=item goto <identifier>

B<branch> <identifier>.

=item if <var> goto <identifier>

=item unless <var> goto <identifier>

Translate to B<if x, identifier> or B<unless ..>.

=item if <var> <relop> <var> goto <identifier>

The B<relop> B<<, <=, ==, != E<gt>= E<gt>> translate to the PASM opcodes
B<lt>, B<le>, B<eq>, B<ne>, B<ge> or B<gt> B<var>, B<var>,
B<identifier>.

=item unless <var> <relop> <var> goto <identifier>

Like above, but branch if condition isn't met.

=item <var> = <var>

B<set var, var>

=item <var> = <unary> <var>

The B<unary>s B<!>, B<-> and B<~> generate B<not>, B<neg> and B<bnot> ops.

=item <var> = <var> <binary> <var>

The B<binary>s B<+>, B<->, B<*>, B</>, B<%> and B<**> generate
B<add>, B<sub>, B<mul>, B<div>, B<mod> and B<pow> arithmetic ops.
B<binary> B<.> is B<concat> and valid for string arguments.

B<<<> and B<E<gt>E<gt>> are arithmetic shifts B<shl> and B<shr>.
B<E<gt>E<gt>E<gt>> is the logical shift B<lsr>.

B<&&>, B<||> and B<~~> are logic B<and>, B<or> and B<xor>.

B<&>, B<|> and B<~> are binary B<band>, B<bor> and B<bxor>.

=item <var> = <var> [ <var> ]

This generates either a keyed B<set> operation or B<substr var, var,
var, 1> for string arguments and an integer key.

=item <var> [ <var> ] = <var>

A keyed B<set> operation or the assign B<substr> op with a length of
1.

=item <var> = new <type>

B<new var, .type>

=item <var> = new <type>, <var>

B<new var, .type, var>

=item <var> = defined <var>

B<defined var, var>

=item <var> = defined <var> [ <var> ]

B<defined var, var[var]> the keyed op.

=item global "string" = <var>

B<store_global "string", var>

=item <var> = global "string"

B<find_global var, "string">

=item <var> = clone <var>

B<clone var, var>

=item <var> = addr <var>

B<set_addr var, var>

=back

=head1 SEE ALSO

F<parsing.pod>, F<calling_conventions.pod>

=head1 FILES

F<imcc.l>, F<imcc.y>

=head1 AUTHOR

Leopold Toetsch <lt@toetsch.at>

=cut

