Add support for converting string to num using '+' prefix.

README.md

@@ -64,7 +64,7 @@ Table of Contents
   * [Useful Utilities](#useful-utilities)
   * [Document generator](#document-generator)
   * [Syntax Highlight](#syntax-highlight)
-  * [Futual Plans](#futual-plans)
+  * [Future Plans](#future-plans)
   * [License](#license)
 
 ## Summary
@@ -1088,6 +1088,20 @@ revStr = reverse(str)
 println("Reverse str =", revStr)
 ```
 
+If you hava a string, you want to convert it to number, you could add a "+" prefix before the string.
+
+```swfit
+a = +"121314" // a is an int
+println(a) // result: 121314
+
+// Integer also support "0x"(hex), "0b"(binary), "0c"(octal) prefix
+a = +"0x10" // a is an int
+println(a) // result: 16
+
+a = +"121314.6789" // a is a float
+println(a) // result: 121314.6789
+```
+
 ### Hash
 In monkey, the builtin hash will keep the order of keys when they are added to the hash, just like python's orderedDict.
 

README_cn.md

@@ -1092,6 +1092,20 @@ revStr = reverse(str)
 println("Reverse str =", revStr)
 ```
 
+如果你希望将一个包含数字的字符串转换为数字，你可以在字符串之前加入"+“号，将此字符串转换为数字：
+
+```swfit
+a = +"121314" // a是一个整数
+println(a) // 结果：121314
+
+// 整数支持"0x"(十六进制), "0b"(二进制), "0c"(八进制)前缀
+a = +"0x10" // a是一个整数
+println(a) // 结果：16
+
+a = +"121314.6789" // a是一个浮点数
+println(a) // 结果：121314.6789
+```
+
 ### 哈希(Hash)
 在monkey中，哈希默认会保持Key的插入顺序，类似Python的orderedDict.
 

src/monkey/eval/eval.go

@@ -12,6 +12,7 @@ import (
 	"regexp"
 	"runtime"
 	"runtime/debug"
+	"strconv"
 	"strings"
 	"sync"
 	"unicode/utf8"
@@ -1427,7 +1428,40 @@ func evalPrefixExpression(p *ast.PrefixExpression, scope *Scope) Object {
 	case "!":
 		return evalBangOperatorExpression(right)
 	case "+":
-		return right
+		switch right.Type() {
+		case STRING_OBJ:
+			var n int64
+			var err error
+
+			var content = right.(*String).String
+			if content[len(content)-1] == 'u' {
+				content = content[:len(content)-1]
+			}
+
+			if strings.HasPrefix(content, "0b") {
+				n, err = strconv.ParseInt(content[2:], 2, 64)
+			} else if strings.HasPrefix(content, "0x") {
+				n, err = strconv.ParseInt(content[2:], 16, 64)
+			} else if strings.HasPrefix(content, "0c") {
+				n, err = strconv.ParseInt(content[2:], 8, 64)
+			} else {
+				n, err = strconv.ParseInt(content, 10, 64)
+				if err != nil {
+					// Check if it is a float
+					var f float64
+					f, err = strconv.ParseFloat(content, 64)
+					if err == nil {
+						return NewFloat(f)
+					}
+				}
+			}
+			if err != nil {
+				panic(NewError(p.Pos().Sline(), PREFIXOP, p, right.Type()))
+			}
+			return NewInteger(n)
+		default:
+			return right
+		}
 	case "-":
 		switch right.Type() {
 		case INTEGER_OBJ: