rhai/tests/syntax.rs

use rhai::{
    Engine, EvalAltResult, EvalContext, Expression, ParseError, ParseErrorType, Scope, INT,
};

#[test]
fn test_custom_syntax() -> Result<(), Box<EvalAltResult>> {
    let mut engine = Engine::new();

    engine.consume("while false {}")?;

    // Disable 'while' and make sure it still works with custom syntax
    engine.disable_symbol("while");
    assert!(matches!(
        *engine.compile("while false {}").expect_err("should error").0,
        ParseErrorType::Reserved(err) if err == "while"
    ));
    assert!(matches!(
        *engine.compile("let while = 0").expect_err("should error").0,
        ParseErrorType::Reserved(err) if err == "while"
    ));

    engine
        .register_custom_syntax(
            &[
                "do", "|", "$ident$", "|", "->", "$block$", "while", "$expr$",
            ],
            1,
            |engine: &Engine,
             context: &mut EvalContext,
             scope: &mut Scope,
             inputs: &[Expression]| {
                let var_name = inputs[0].get_variable_name().unwrap().to_string();
                let stmt = inputs.get(1).unwrap();
                let expr = inputs.get(2).unwrap();

                scope.push(var_name, 0 as INT);

                loop {
                    engine.eval_expression_tree(context, scope, stmt)?;

                    if !engine
                        .eval_expression_tree(context, scope, expr)?
                        .as_bool()
                        .map_err(|_| {
                            EvalAltResult::ErrorBooleanArgMismatch(
                                "do-while".into(),
                                expr.position(),
                            )
                        })?
                    {
                        break;
                    }
                }

                Ok(().into())
            },
        )
        .unwrap();

    // 'while' is now a custom keyword so this it can no longer be a variable
    engine.consume("let while = 0").expect_err("should error");

    assert_eq!(
        engine.eval::<INT>(
            r"
                do |x| -> { x += 1 } while x < 42;
                x
            "
        )?,
        42
    );

    // The first symbol must be an identifier
    assert!(matches!(
        *engine.register_custom_syntax(&["!"], 0, |_, _, _, _| Ok(().into())).expect_err("should error"),
        ParseError(err, _) if *err == ParseErrorType::BadInput("Improper symbol for custom syntax: '!'".to_string())
    ));

    Ok(())
}