Return an expression or decide how to continue about peggy HOT 4 CLOSED

If I correctly understand your needs, you have a two ways to do that:

• just use choice operator

  decide
    = integer
    / word
    / ...
    ;

  Remember, that order of alternatives is important! If one rule is a prefix of other (for example, = and ==) the longest should be the first
• you need a some rule that will match your tag and then you can analyze this tag using semantic predicate:

  // returns array [tag_result, rule_result]
  decide = tag:tag (
      &{ return isInteger(tag); } @integer
    / &{ return isWord(tag); } @word
    / ...
  );

  Because probably the tags will uniquely determine the type, the order not so important, but the right order can make grammar faster. Put more expected alternatives first

from peggy.

Good idea, thanks.
Do you know if I can have in the grammar (I am using CLI to generate my parser at compile time throught npm run build command) a mix of static and dynamic rules?

integer = [0-9]+ // static rule
word = [a-z]i+ // static rule
entry = tag `${some generated rule that makes the grammar}` // dynamic rule generated through javascript code

I understand it is a bit fuzzy but I am new to parser generators. Thanks for the help and patience.

from peggy.

You cannot have ${some generated rule that makes the grammar} in the grammar itself, but you can generate your grammar before running the CLI. You also could write a plugin that will append necessary rules directly to the AST instead of generating grammar text. If you want, you can even write that plugin in that way, that is would read its input from the same grammar file, so technically your grammar will contain both static and dynamic rules:

{{
  // For example, you does not use top-level initializer and
  // you decide to write some code inside it for your plugin
}}
integer = [0-9]+ // static rule
word = [a-z]i+ // static rule

// dynamic rules will be injected to the AST by plugin, 
// plugin take their input from `ast.topLevelInitializer`

from peggy.

I'm going to close this. Please reopen if there is a concrete feature to request.

from peggy.