definePhrasePattern

function definePhrasePattern(opts): PrefixParselet;

Defined in: packages/engine/src/parser/PhrasePattern.ts:102

Build a PrefixParselet from a declarative list of phrase alternatives, instead of hand-writing parser.consume()/ parser.parseExpression() call sequences.

Covers the “keyword slot keyword slot keyword” shape shared by most of this codebase’s phrase-grammar parselets (roll between X and Y, clamp X between Y and Z, average of X, Y, Z’s single-item case, etc.) with one well-tested consumption/error-handling core, rather than each parselet re-deriving its own, the class of bug this is meant to prevent (a hand-rolled parselet mishandling an alternative-phrasing or precedence edge case) is exactly what produced real, shipped bugs this session (Dice’s bare-hyphen range, Vector’s tuple-vs-group ambiguity).

Parameters

Parameter	Type
opts	{ alternatives: PhraseAlternative[]; category: string; }
opts.alternatives	PhraseAlternative[]
opts.category	string

Returns

PrefixParselet

Example

// "roll between X and Y" / "roll from X to Y"
definePhrasePattern({
  category: "Dice",
  alternatives: [
    {
      slots: [
        { kind: "keyword", tokenTypes: ["BETWEEN"] },
        { kind: "expr" },
        { kind: "keyword", tokenTypes: ["AND"] },
        { kind: "expr" },
      ],
      emit: (builder) => {
        builder.emitOpcode(OpCode.CALL_BUILTIN);
        builder.emitIndex(DICE_ROLL_BUILTIN);
        builder.emitIndex(2);
      },
    },
  ],
});