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4.1 User Code Blocks

4 Propane Grammar File

A Propane grammar file provides Propane with the patterns, tokens, grammar rules, and user code blocks from which to build the generated lexer and parser.

Example grammar file:

<<
import std.math;
>>

# Parser values are unsigned integers.
ptype ulong;

# A few basic arithmetic operators.
token plus /\\+/;
token times /\\*/;
token power /\\*\\*/;
token integer /\\d+/ <<
  ulong v;
  foreach (c; match)
  {
    v *= 10;
    v += (c - '0');
  }
  $$ = v;
>>
token lparen /\\(/;
token rparen /\\)/;
# Drop whitespace.
drop /\\s+/;

Start -> E1 <<
  $$ = $1;
>>
E1 -> E2 <<
  $$ = $1;
>>
E1 -> E1 plus E2 <<
  $$ = $1 + $3;
>>
E2 -> E3 <<
  $$ = $1;
>>
E2 -> E2 times E3 <<
  $$ = $1 * $3;
>>
E3 -> E4 <<
  $$ = $1;
>>
E3 -> E3 power E4 <<
  $$ = pow($1, $3);
>>
E4 -> integer <<
  $$ = $1;
>>
E4 -> lparen E1 rparen <<
  $$ = $2;
>>

Grammar files can contain comment lines beginning with # which are ignored. White space in the grammar file is also ignored.

It is convention to use the extension .propane for the Propane grammar file, however any file name is accepted by Propane.

This user guide follows the convention of beginning a token name with a lowercase character and beginning a rule name with an uppercase character.

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4.1 User Code Blocks