Experimental .cge.md

Experimental model specification — syntax may evolve before 1.0.

A .cge.md file combines explanation and a formal model specification. The crucial rule is simple:

Markdown prose never controls computation.

Only fenced blocks marked cge are parsed. No LLM infers an omitted equation, closure choice, or parameter from prose.

MVP grammar

set goods = [FOOD, MFG]
param alpha[FOOD] = 0.5
var p[i in goods] > 0

equation some_equation:
    left_hand_side = right_hand_side

fix p[FOOD] = 1
drop redundant_equation
shockable alpha

Expressions support numeric constants, Python-style identifiers (letters, digits, _), one- or multi-dimensional indexing, arithmetic, powers, and sum(i in set, expression) / prod(i in set, expression). Set members also use grammar-0 identifiers in this first version; quoted/string-valued members are not yet supported. Equation declarations use exactly one standalone =; comparison operators such as >= and == are rejected with a source-located diagnostic. Parameter-only identities are rejected because they are data checks, not equilibrium constraints.

Strict variable bounds (> / <) are represented by the nearest floating-point value inside the open interval using math.nextafter, avoiding a fixed absolute epsilon that changes meaning with scale.

External data can be declared as a provenance-bearing reference:

data SAM = "sam.csv"

Grammar version 0 does not silently interpret arbitrary CSVs as model semantics; richer data bindings can be added explicitly in later grammar versions.

Validate

cge check examples/custom_markdown_model/two_good_exchange.cge.md

Errors carry file/line locations.

Solve

cge solve examples/custom_markdown_model/two_good_exchange.cge.md

The first compiler target is intentionally small. StandardCGE, CAMCGE and IFPRI are not rewritten in this DSL merely to prove that the language exists.