type checking and error handling for builtins improved.

evaluator/evaluator_test.go

@@ -398,24 +398,24 @@ func TestBuiltinFunctions(t *testing.T) {
 		{`len("")`, 0},
 		{`len("four")`, 4},
 		{`len("hello world")`, 11},
-		{`len(1)`, errors.New("argument to `len` not supported, got int")},
-		{`len("one", "two")`, errors.New("wrong number of arguments. got=2, want=1")},
+		{`len(1)`, errors.New("TypeError: object of type 'int' has no len()")},
+		{`len("one", "two")`, errors.New("TypeError: len() takes exactly 1 argument (2 given)")},
 		{`len("∑")`, 1},
 		{`len([1, 2, 3])`, 3},
 		{`len([])`, 0},
 		{`first([1, 2, 3])`, 1},
 		{`first([])`, nil},
-		{`first(1)`, errors.New("argument to `first` must be array, got int")},
+		{`first(1)`, errors.New("TypeError: first() expected argument #1 to be `array` got `int`")},
 		{`last([1, 2, 3])`, 3},
 		{`last([])`, nil},
-		{`last(1)`, errors.New("argument to `last` must be array, got int")},
+		{`last(1)`, errors.New("TypeError: last() expected argument #1 to be `array` got `int`")},
 		{`rest([1, 2, 3])`, []int{2, 3}},
 		{`rest([])`, nil},
 		{`push([], 1)`, []int{1}},
-		{`push(1, 1)`, errors.New("argument to `push` must be array, got int")},
+		{`push(1, 1)`, errors.New("TypeError: push() expected argument #1 to be `array` got `int`")},
 		{`print("Hello World")`, nil},
 		{`input()`, ""},
-		{`pop([])`, errors.New("cannot pop from an empty array")},
+		{`pop([])`, errors.New("IndexError: pop from an empty array")},
 		{`pop([1])`, 1},
 		{`bool(1)`, true},
 		{`bool(0)`, false},