raising events appears to work. nondeterminism currently ignored

src/VisualEditor/actionlang_interpreter.ts

@@ -0,0 +1,46 @@
+// Just a simple recursive interpreter for the action language
+
+import { Expression } from "./label_ast";
+import { Environment } from "./runtime_types";
+
+
+const UNARY_OPERATOR_MAP: Map<string, (x: any) => any> = new Map([
+  ["!", x => !x],
+  ["-", x => -x as any],
+]);
+const BINARY_OPERATOR_MAP: Map<string, (a: any, b: any) => any> = new Map([
+  ["+", (a, b) => a + b],
+  ["-", (a, b) => a - b],
+  ["*", (a, b) => a * b],
+  ["/", (a, b) => a / b],
+  ["&&", (a, b) => a && b],
+  ["||", (a, b) => a || b],
+  ["==", (a, b) => a == b],
+  ["<=", (a, b) => a <= b],
+  [">=", (a, b) => a >= b],
+  ["<", (a, b) => a < b],
+  [">", (a, b) => a > b],
+]);
+
+export function evalExpr(expr: Expression, environment: Environment): any {
+  if (expr.kind === "literal") {
+    return expr.value;
+  }
+  else if (expr.kind === "ref") {
+    const found = environment.get(expr.variable);
+    if (found === undefined) {
+      throw new Error(`variable '${expr.variable}' does not exist in environment`);
+    }
+    return found;
+  }
+  else if (expr.kind === "unaryExpr") {
+    const arg = evalExpr(expr.expr, environment);
+    return UNARY_OPERATOR_MAP.get(expr.operator)!(arg);
+  }
+  else if (expr.kind === "binaryExpr") {
+    const lhs = evalExpr(expr.lhs, environment);
+    const rhs = evalExpr(expr.rhs, environment);
+    return BINARY_OPERATOR_MAP.get(expr.operator)!(lhs, rhs);
+  }
+  throw new Error("should never reach here");
+}