Add custom syntax.

tests/syntax.rs

@@ -0,0 +1,69 @@
+#![cfg(feature = "internals")]
+use rhai::{
+    Dynamic, Engine, EvalAltResult, EvalState, Expr, Imports, LexError, Module, Scope, INT,
+};
+
+#[test]
+fn test_custom_syntax() -> Result<(), Box<EvalAltResult>> {
+    let mut engine = Engine::new();
+
+    engine
+        .add_custom_syntax(
+            &["do", "$ident$", "$block$", "while", "$expr$"],
+            1,
+            |engine: &Engine,
+             scope: &mut Scope,
+             mods: &mut Imports,
+             state: &mut EvalState,
+             lib: &Module,
+             this_ptr: &mut Option<&mut Dynamic>,
+             exprs: &[Expr],
+             level: usize| {
+                let var_name = match exprs.get(0).unwrap() {
+                    Expr::Variable(s) => (s.0).0.clone(),
+                    _ => unreachable!(),
+                };
+                let stmt = exprs.get(1).unwrap();
+                let expr = exprs.get(2).unwrap();
+
+                scope.push(var_name, 0 as INT);
+
+                loop {
+                    engine.eval_expr_from_ast(scope, mods, state, lib, this_ptr, stmt, level)?;
+
+                    if !engine
+                        .eval_expr_from_ast(scope, mods, state, lib, this_ptr, expr, level)?
+                        .as_bool()
+                        .map_err(|_| {
+                            EvalAltResult::ErrorBooleanArgMismatch(
+                                "do-while".into(),
+                                expr.position(),
+                            )
+                        })?
+                    {
+                        break;
+                    }
+                }
+
+                Ok(().into())
+            },
+        )
+        .unwrap();
+
+    assert!(matches!(
+        *engine.add_custom_syntax(&["!"], 0, |_, _, _, _, _, _, _, _| Ok(().into())).expect_err("should error"),
+        LexError::ImproperSymbol(s) if s == "!"
+    ));
+
+    assert_eq!(
+        engine.eval::<INT>(
+            r"
+                do x { x += 1 } while x < 42;
+                x
+            "
+        )?,
+        42
+    );
+
+    Ok(())
+}