Grammar

Glossia uses a two-layer grammar system: a context-free grammar (CFG) layer that generates POS tag sequences, and a type-driven layer based on Montague Grammar that constrains POS slots via lambda calculus.

Grammar Files

Grammars are defined in YAML files located in languages/{language}/grammar.yaml. Each grammar file specifies:

Types: Montague Grammar semantic types for each POS tag
Rules: CFG production rules with weights and lambda terms

Example Grammar (English)

grammar:
  name: "English Grammar"

  types:
    - name: "N"
      lambda_type: "e -> t"
    - name: "V"
      lambda_type: "e -> (e -> t)"
    - name: "Adj"
      lambda_type: "e -> e"
    - name: "Det"
      lambda_type: "(e -> t) -> (e -> t)"
    - name: "Cop"
      lambda_type: "(e -> t) -> (e -> t)"
    - name: "Dot"
      lambda_type: "t"

  rules:
    sentence:
      lambda: "N"
      cfg_productions:
        - production: "NP VP Dot"
          weight: 0.85
          lambda: "N"
        - production: "NP Adv V NP Dot"
          weight: 0.10
          lambda: "N"
        - production: "NP V NP Dot"
          weight: 0.05
          lambda: "N"

    noun_phrase:
      lambda: "N"
      cfg_productions:
        - production: "N"
          weight: 1.0
          lambda: "N"
        - production: "Det[def] N"
          weight: 0.50
          lambda: "Det"
        - production: "Det[indef] N"
          weight: 0.25
          lambda: "Det"

    verb_phrase:
      lambda: "N"
      cfg_productions:
        - production: "VP_BASE"
          weight: 0.70
          lambda: "N"
        - production: "VP_BASE VP_PP_TAIL"
          weight: 0.30
          lambda: "N"

Key Syntax

Terminal symbols are POS tags: Det, Adj, N, V, Modal, Aux, Cop, To, Prep, Adv, Conj, Dot, Prefix
Refinement tags in brackets constrain cover word selection: Det[def] selects definite determiners ("the"), Det[indef] selects indefinite ("a", "an"), Det[quant] selects quantifiers ("each", "some")
Weights determine probabilistic selection between alternative productions
Rule names map to standard abbreviations: noun_phrase -> NP, verb_phrase -> VP, sentence -> S

POS Tags

Glossia uses 13 parts of speech:

POS	Description	Example Words
`Det`	Determiner	the, a, each, some
`Adj`	Adjective	big, red, fast
`N`	Noun	cat, house, time
`V`	Verb	run, see, get
`Modal`	Modal verb	may, can, might
`Aux`	Auxiliary verb	has, will, does
`Cop`	Copula	is, are, was
`To`	Infinitive marker	to
`Prep`	Preposition	in, on, for, to
`Adv`	Adverb	very, already, out
`Conj`	Conjunction	and, but, or
`Dot`	Sentence terminator	.
`Prefix`	Sentence prefix	Re:, Fwd:

POS Slot Constraints

Payload-eligible POS: N, V, Adj, Adv, Prep, Det, Conj - these slots can be filled with either payload or cover words
Cover-only POS: Aux, Cop, To, Prefix, Dot, Modal - these slots are always filled with cover (function) words

Montague Grammar Type System

Each POS tag maps to a semantic type from Montague Grammar:

POS	Type	Interpretation
N	`e -> t`	Predicate over entities
V	`e -> (e -> t)`	Relation between entities
Adj	`e -> e`	Entity modifier
Adv	`(e -> t) -> (e -> t)`	Predicate modifier
Det	`(e -> t) -> (e -> t)`	Quantifier
Prep	`e -> (e -> t)`	Prepositional relation
Conj	`t -> (t -> t)`	Proposition connective
Cop	`(e -> t) -> (e -> t)`	Subject-predicate linker
Modal/Aux/To	`(e -> t) -> (e -> t)`	Predicate modifier
Dot	`t`	Sentence truth value
Prefix	`t -> t`	Sentence wrapper

Where:

e = Entity type
t = Truth value type
-> = Function type

These types ensure that constituents combine in semantically valid ways, beyond what the CFG alone can enforce.

Dialect Support

Grammar files can define dialect overlays that modify the base rules for different generation modes. Dialects are defined in a separate dialect.yaml file:

dialects:
  subject:
    rules:
      sentence:
        cfg_productions:
          - production: "Prefix NP Cop Adj Dot"
            weight: 0.30
          - production: "NP Cop Adj Dot"
            weight: 0.70

  poetry:
    rules:
      sentence:
        cfg_productions:
          - production: "NP VP Dot"
            weight: 0.50
          - production: "Adj N V Adv Dot"
            weight: 0.50

The --dialect subject and --dialect body flags select which dialect overlay to apply on top of the base grammar rules.

Sentence Length Strategy

The grammar interacts with the length mode to control output:

Compact mode: Tries sentence lengths from k_min to k_max, stopping at the first length where the payload fits. Within that length, picks the highest-probability POS sequence.
Natural mode: Samples sentence length from the grammar's probability distribution across all valid lengths. This produces more varied, natural-sounding text.

The scoring function for balancing compactness vs naturalness:

score = log P(sequence) - λ * length

Higher λ yields shorter text; lower λ yields more natural text.

Glossia Documentation