Lets build a simple interpreter from scratch in python, pt.08: For loop

In this post we are implementing the 'for' loop:

class Interpreter:
    def __init__(self):
        self.scope=[{}]
        self.loop_stack=[]

    # ...(previous code)...

    # 'For' loop is not much different from 'while' loop
    # for(inits; cond; increments) {block}

    def For(self,xs):
        self.loop_stack.append({"break":False,"continue":False})        
        _, inits, cond, increments, block = xs
        for x in inits: 
            self.eval(x)
        while self.eval(cond):
            if isinstance(block[0],list):
                for x in block:
                    self.eval(x)
                    if self.loop_stack[-1]["break"]:
                        self.loop_stack.pop()
                        return
                    if self.loop_stack[-1]["continue"]:
                        self.loop_stack[-1]["continue"]=False
                        break
            else:
                self.eval(block) 
            for x in increments:
                self.eval(x)
        self.loop_stack.pop()

code=[

    ["Set","sum",0],

    ["For", [["Set","i",0]], 
            ["Lt", ["Get","i"], 100], 
            [["Set","i", ["Add",["Get","i"], 1] ]],   
    [   

        ["Set","sum", ["Add",["Get", "sum"],["Get","i"]]],

        ["Print","i=",["Get","i"],", sum=",["Get","sum"]],

        ["If", ["Eq", ["Get", "i"], 10], 
             ["Break"],[]
        ],


    ]],

]

interpreter=Interpreter()

interpreter.run(code)

Output:

i=0, sum=0
i=1, sum=1
i=2, sum=3
i=3, sum=6
i=4, sum=10
i=5, sum=15
i=6, sum=21
i=7, sum=28
i=8, sum=36
i=9, sum=45
i=10, sum=55

Link to complete code.

Part 9: Function,Call,Return