用Go实现一门解释型语言

原文作者：高峰

A interpreter language implementation in Go

1 Introduction

Write an Interpreter in Go source code.

Monkey interpreter language which is implemented Go language. After typing monkey in terminal, you get into the monkeyprogramming language.

1 $ ./monkey
2 Hello $Username! This is Monkey programming language!
3 Feel free to type in commnd
4 Enter "exit()" or CTRL+C to quit command interface
5 >>>

2 Syntax

2.1 Definition

using let as keyword, each line ends with ;.

1 >>>let a = 3;
2 >>>let b = 1.2;
3 >>>a+b
4 4.2

2.2 Arithmetic operations

monkey supports all basic arithmetic operation of int and float types. int type is represented by int64 and float type is represented by float64.

 1 >>> let a = 3;
 2 >>> let b = 1.2;
 3 >>> a + b
 4 4.2
 5 >>> a - b
 6 1.8
 7 >>> a * b 
 8 3.6
 9 >>> a / b 
10 2.5

2.3 Builtin containers

monkey contains two builtin containers: array and map.

• array

array is a list which organizes items by linear sequence. But types of items can be different from each other.

1 >>> let a = [1, 2.3, "array"];
2 >>> a 
3 [1, 2.3, array]
4 >>> let b = push(a, "another");
5 >>> b 
6 [1, 2.3, array, another]

• map

map is treated as key-value container. please attention to that only boolean, int and string types can be used as key.

 1 >>> let a = {"name":"moneky", true:1, 7:"sevent"};
 2 >>> a
 3 {name: monkey, true: 1, 7: seven}
 4 >>> a["name"]
 5 monkey
 6 >>> a[true]
 7 1
 8 >> a[7]
 9 seven
10 >>>let b = set(a, 8, "eight");
11 >>> b 
12 {name: moneky, true: 1, 7: sevent, 8: eight}

2.4 Builtin functions

• len

yield the length of builtin containers.

• first

yield the first element of array.

• last

yield the last element of array.

• rest

yield an array which excludes the first element.

• push

push an elements into the array.

• set

insert key value pair into the map

• puts

print literal value of objects.

2.5 Function

monkey use fn as the definition of function. Apart from regular function using, monkey also includes high order function.

1 >>>let add = fn(a, b) { return a + b;};
2 >>> add(1,2)
3 3
4 >>>let addTwo = fn(a,b, f) { return 2 + f(a, b);};
5 >>>addTwo(1,2, add)
6 5

2.5 If-else statements

monkey supports if-else statements.

1 >>> let max = fn(a, b) { if (a > b) { return a;} else { return b; } };
2 >>> max(1, 2)
3 2

2.6 For-loop statements

monkey support for-loop statement.

1 >>> let sum = fn(x) { let i = 1; let sum = 0; for (i < x) { let sum = sum + i; let i = i+1; } return sum; };
2 >>> sum(100)
3 4950

3 Extensions

To make monkey interpreter language to be more powerfull, it is deserved improving it.

• float type
• unicode literal
• loop branch
• translate into Chinese
• ...

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