Done with arrays and all its associated builtins

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

pkg/evaluator/builtins.go

@@ -1,6 +1,10 @@
 package evaluator
 
-import "code.jmug.me/jmug/interpreter-in-go/pkg/object"
+import (
+	"os"
+
+	"code.jmug.me/jmug/interpreter-in-go/pkg/object"
+)
 
 var builtins = map[string]*object.Builtin{
 	"len": {
@@ -13,10 +17,96 @@ var builtins = map[string]*object.Builtin{
 			switch arg := args[0].(type) {
 			case *object.String:
 				return &object.Integer{Value: int64(len(arg.Value))}
+			case *object.Array:
+				return &object.Integer{Value: int64(len(arg.Elements))}
 			default:
 				return newError("argument to `len` not supported, got %s",
 					args[0].Type())
 			}
 		},
 	},
+	"first": {
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1",
+					len(args))
+			}
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `first` must be ARRAY, got %s",
+					args[0].Type())
+			}
+
+			arr := args[0].(*object.Array)
+			if len(arr.Elements) > 0 {
+				return arr.Elements[0]
+			}
+
+			return _NULL
+		},
+	},
+	"last": {
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1",
+					len(args))
+			}
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `last` must be ARRAY, got %s",
+					args[0].Type())
+			}
+
+			arr := args[0].(*object.Array)
+			if len(arr.Elements) > 0 {
+				return arr.Elements[len(arr.Elements)-1]
+			}
+			return _NULL
+		},
+	},
+	"rest": {
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1",
+					len(args))
+			}
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `rest` must be ARRAY, got %s",
+					args[0].Type())
+			}
+			arr := args[0].(*object.Array).Elements
+			arrLen := len(arr)
+			if arrLen > 0 {
+				newArr := make([]object.Object, arrLen-1)
+				copy(newArr, arr[1:])
+				return &object.Array{Elements: newArr}
+			}
+			return _NULL
+		},
+	},
+	"push": {
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 2 {
+				return newError("wrong number of arguments. got=%d, want=2",
+					len(args))
+			}
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `push` must be ARRAY, got %s",
+					args[0].Type())
+			}
+			arr := args[0].(*object.Array).Elements
+			arrLen := len(arr)
+			newArr := make([]object.Object, arrLen+1)
+			copy(newArr, arr)
+			newArr[arrLen] = args[1]
+			return &object.Array{Elements: newArr}
+		},
+	},
+	"exit": {
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 0 {
+				return newError("exit takes no arguments...")
+			}
+			os.Exit(0)
+			return nil // Make the compiler happy.
+		},
+	},
 }