NAME ^

IMCC - parsing

OVERVIEW ^

This document describes the basic parsing functionality of IMCC.

DESCRIPTION ^

IMCC parses and generates code in terms of compilation units. These are self-contained blocks of code very similar to subroutines.

Code for a compilation unit is created as soon (or not earlier) as the end of the unit is reached.

General imcc syntax ^

        program: subs

        subs: statements ...

Comments ^

Comments start with #, which may appear at any point on a line, and end at the end of the line.

POD sections ^

Everything enclosed in POD markers is ignored.

        =some_pod_marker in col 1
        ...
        =cut

A POD section starts with a = in column 1 and ends with a =cut on a line on its own.

Compilation units ^

Subroutines: .sub ... .end ^

This code:

        .sub name
                statements
                ...
        .end

Defines a subroutine with the entry point _name, using the Parrot calling conventions. See docs/calling_conventions.pod for more details.

Assembly blocks .emit ... .eom ^

This code:

        .emit
        _sub1:
                pasm_statements
                ...
                ret
        ...
        .eom

defines a compilation unit containing PASM statements only. Typical usage is for language initialization and builtins code.

Code outside compilation units ^

Any code appearing outside of a compilation unit will be ignored (if not now, then in the near future).

Nested subs ^

Nested subroutines are not supported.

Symbols, constants and labels ^

Compilation units maintain their own symbol table containing local labels and variable symbols. This symbol table, hash, is not visible to code in different units.

If you need global variables, please use the global opcode.

Global labels and constants are kept in the global symbol table ghash. This allows for global constant folding beyond the scope of individual subroutines.

This also means that you currently can't use the same global symbol (e.g. subroutine name) in different namespaces. The following creates invalid code:

  .sub main
     ...
  .end

   .namespace ["main"]
  .sub main
     ...
  .end

Local labels in different compilation units with the same name are allowed, though assembling the generated PASM doesn't work. However, running this code inside imcc is ok. This will probably change in the future so that local labels are mangled to be unique.

SEE ALSO ^

docs/calling_conventions.pod

FILES ^

imcc.y, instructions.c, t/compilers/imcc/syn/sub.t, t/compilers/imcc/imcpasm/sub.t, t/compilers/imcc/syn/scope.t

AUTHOR ^

Leopold Toetsch <lt@toetsch.at>


 parrot