add compiler support for expression lines.

src/compile.mjs

@@ -70,6 +70,25 @@ export function compile_line (env, line) {
 		};
 	}
 
+	if (line.type === Line.Expression) {
+		let value;
+		let valid = true;
+
+		try {
+			value = evaluate(env, line.value);
+		} catch (e) {
+			valid = false;
+		}
+
+		if (!valid) return invalid();
+
+		return {
+			valid: true,
+			env: env,
+			value: value,
+		};
+	}
+
 	return invalid();
 }