Grammar reference

Grammar formats and syntax.

GLRMask accepts JSON Schema, GLRM, Lark, and EBNF.

Constraint constructors

input	Python constructor	typical use
JSON Schema	`Constraint.from_json_schema(...)`	structured JSON, tools, typed API responses
GLRM	`Constraint.from_glrm_grammar(...)`	native grammar/lexer control, reusable subgrammars
Lark	`Constraint.from_lark(...)`	existing Lark grammars
EBNF	`Constraint.from_ebnf(...)`	conventional CFG descriptions

DynamicConstraint has matching constructors.

JSON Schema

GLRMask supports a subset of JSON Schema. Unsupported features may be rejected.

GLRM

GLRM is GLRMask’s native grammar format. A grammar begins with glrm 1; and a start declaration. Rules use = and end with ;.

glrm 1;
start value;

t WS = /[ \t\r\n]+/;
ignore WS;

t NUMBER = /-?(0|[1-9][0-9]*)/;
nt value = NUMBER | "null";

Use explicit eps for epsilon. Regex terminals use full-match semantics. Unsupported or non-regular regex constructs are rejected.

External subgrammars

Declare a child grammar by name and bind a compiled constraint in Python:

extern grammar payload;

payload = glrmask.Constraint.from_json_schema(payload_schema, vocab)

document = glrmask.Constraint.from_glrm_grammar(
    grammar,
    vocab,
    subgrammars={"payload": payload},
)

Inline and externally bound subgrammars have the same semantics:

g inner = {
    start value;
    nt value = "null";
};

Special tokens

To use a special token in a GLRM grammar, declare it by name:

glrm 1;
start message;
extern token TOOL_CALL;
nt message = TOOL_CALL call;
nt call = "lookup()";

Bind it outside the grammar:

constraint = glrmask.Constraint.from_glrm_grammar(
    grammar,
    vocab,
    bindings={"TOOL_CALL": tool_call_token_id},
)

Direct finite automata

A terminal or nonterminal can use an explicit finite automaton body:

t WORD = fa {
    start begin;
    accept done;
    begin -> middle: "a";
    middle -> done: "b";
};

End tokens

End tokens are handled by the decoder. If the constraint is accepting, generation may stop without committing another token.