Crate maplibre_expr 

maplibre_expr — a pure-Rust parser and evaluator for MapLibre GL style expressions.

The crate turns a MapLibre expression (a serde_json::Value such as ["*", ["get", "x"], 2]) into an Expr tree with parse, then evaluates that tree against an EvaluationContext with evaluate.

use maplibre_expr::{parse, evaluate, EvaluationContext, Feature, Value};
use std::collections::BTreeMap;

let json: serde_json::Value = serde_json::json!(["*", ["get", "x"], 2]);
let expr = parse(&json).unwrap();

let mut props = BTreeMap::new();
props.insert("x".to_string(), Value::Number(21.0));
let ctx = EvaluationContext::new().with_feature(Feature {
    properties: props,
    ..Feature::default()
});

assert_eq!(evaluate(&expr, &ctx).unwrap(), Value::Number(42.0));

Conformance is validated against a vendored snapshot of the maplibre-style-spec expression test fixtures; see tests/spec.rs.

Re-exports

pub use filter::convert_legacy_filter;

pub use filter::is_expression_filter;

pub use filter::FilterError;

Modules

convert

Converting legacy MapLibre function objects into modern expressions.

filter

Converting legacy MapLibre filters into modern expressions.

Structs

Color

An RGBA color with channels stored as floats in the 0.0..=1.0 range.

EvalError

An error raised while evaluating a well-formed expression.

EvaluationContext

Everything an expression can read while evaluating: global parameters such as zoom, the current Feature, and the shared global-state map read by the global-state operator.

Feature

The feature (and its properties) an expression is evaluated against.

Function

An eval-time function: body (raw JSON) is evaluated with params bound to the argument values. May reference itself or other functions (recursion is bounded at runtime).

Macro

A parse-time macro: body is expanded with params bound to the call arguments (as a let). body is raw JSON in the expression grammar.

Options

Parser/runtime extension registry.

ParseError

An error raised while turning JSON into an Expr.

Enums

EvalErrorKind

The semantic cause of an evaluation error.

Expr

A parsed MapLibre expression.

InterpKind

The interpolation curve used by an interpolate expression.

InterpSpace

The color space an interpolate expression blends in.

ParseErrorKind

The semantic cause of a parse/compile error.

Projection

A projection definition value.

Type

A type in the MapLibre expression type lattice.

Value

A value in the MapLibre expression type system.

Functions

evaluate

Evaluate a parsed expression against an evaluation context.

evaluate_with

Evaluate with user Options, so calls to user functions are dispatched to their (recursion-limited) bodies.

parse

Parse a MapLibre expression from its JSON representation.

parse_with

Parse an expression with user Options (macros expand at parse time; function names are accepted as callable operators).

typecheck

Statically type-check a parsed expression, optionally against the type a property expects. On success returns a rewritten tree with type-directed coercion/assertion nodes inserted (evaluate this returned expression so the coercions take effect). Returns a ParseError for expressions the reference implementation rejects at compile time (bad comparisons, malformed match branches, non-interpolatable outputs, misused zoom, and so on).