type checking and error handling for builtins improved.

object/array.go

@@ -14,6 +14,36 @@ func (ao *Array) Type() ObjectType {
 	return ARRAY_OBJ
 }
 
+func (ao *Array) Bool() bool {
+	return len(ao.Elements) > 0
+}
+
+func (a *Array) PopLeft() Object {
+	if len(a.Elements) > 0 {
+		e := a.Elements[0]
+		a.Elements = a.Elements[1:]
+		return e
+	}
+	return &Null{}
+}
+
+func (a *Array) PopRight() Object {
+	if len(a.Elements) > 0 {
+		e := a.Elements[(len(a.Elements) - 1)]
+		a.Elements = a.Elements[:(len(a.Elements) - 1)]
+		return e
+	}
+	return &Null{}
+}
+
+func (a *Array) Prepend(obj Object) {
+	a.Elements = append([]Object{obj}, a.Elements...)
+}
+
+func (a *Array) Append(obj Object) {
+	a.Elements = append(a.Elements, obj)
+}
+
 func (ao *Array) Inspect() string {
 	var out bytes.Buffer
 
@@ -32,9 +62,9 @@ func (ao *Array) String() string {
 	return ao.Inspect()
 }
 
-func (a *Array) Less(i, j int) bool {
-	if cmp, ok := a.Elements[i].(Comparable); ok {
-		return cmp.Compare(a.Elements[j]) == -1
+func (ao *Array) Less(i, j int) bool {
+	if cmp, ok := ao.Elements[i].(Comparable); ok {
+		return cmp.Compare(ao.Elements[j]) == -1
 	}
 	return false
 }