Add tons of builtin helpers and array operations.

object/builtin_join.go

@@ -0,0 +1,27 @@
+package object
+
+import (
+	"strings"
+)
+
+// Join ...
+func Join(args ...Object) Object {
+	if len(args) != 2 {
+		return newError("wrong number of arguments. got=%d, want=1",
+			len(args))
+	}
+
+	if arr, ok := args[0].(*Array); ok {
+		if sep, ok := args[1].(*String); ok {
+			a := make([]string, len(arr.Elements))
+			for i, el := range arr.Elements {
+				a[i] = el.String()
+			}
+			return &String{Value: strings.Join(a, sep.Value)}
+		} else {
+			return newError("expected arg #2 to be `str` got got=%T", args[1])
+		}
+	} else {
+		return newError("expected arg #1 to be `array` got got=%T", args[0])
+	}
+}