feat: better errors for invalid argument types

README.md

@@ -74,7 +74,7 @@ yarn run <tool>
         - Basics (numbers, strings, booleans)
         - String interpolations
         - Array literals/types
-        - Object literals
+        - Object literals/types
     - Array indexing
     - Binary expressions (including compound assignment)
     - Unary expressions (including `++` and `--`)
@@ -87,4 +87,5 @@ yarn run <tool>
 - Type aliases (e.x. `type number = int | float`)
 - `typeof`, `is`
 - `value is in array`
+- Type guards (`value is T`, `"property" is in object`)
 - Classes

src/code-analysis/type-checker/index.ts

@@ -131,10 +131,11 @@ export class TypeChecker implements AST.Visitor.BoundExpression<void>, AST.Visit
     this.check(expr.callee);
 
     const type = <FunctionType>expr.callee.type;
-    const expectedTypes = Array.from(type.parameterTypes.values());
+    const expectedTypes = Array.from(type.parameterTypes.entries());
     for (const arg of expr.args) {
+      const [parameterName, expectedType] = expectedTypes[expr.args.indexOf(arg)];
       this.check(arg);
-      this.assert(arg, arg.type, expectedTypes[expr.args.indexOf(arg)]);
+      this.assert(arg, arg.type, expectedType, `Argument type '${arg.type.toString()}' is not assignable to type '${expectedType.toString()}' of parameter '${parameterName}'`);
     }
   }
 

src/runtime/intrinsics/eval.ts

@@ -5,12 +5,12 @@ import Intrinsic from "../values/intrinsic";
 export default class Eval extends Intrinsic.Function {
   public readonly name = "eval";
   public readonly returnType = new SingularType("any");
-  public readonly argumentTypes = { code: new SingularType("string") };
+  public readonly argumentTypes = { source: new SingularType("string") };
 
-  public call(code: string): ValueType {
+  public call(source: string): ValueType {
     const enclosingResultOutputEnabled = this.interpreter!.host.executionOptions.outputResult;
     this.interpreter!.host.executionOptions.outputResult = false;
-    const result = this.interpreter!.host.doString(code);
+    const result = this.interpreter!.host.doString(source);
     this.interpreter!.host.executionOptions.outputResult = enclosingResultOutputEnabled;
     return result;
   }