[Use python self-made programming language] Part 3

Preface

I have done a programming language: mylang

Start

In fact, the if should be first, but in order to maintain the concept of "explain the single-branch structure first, then the multi-branch structure", the if is passed

Source code

def parse_while(block):
    global status
    try:
        foo = block.split('\n')[0][6:-2]
    except:
        return ['error','WhileSentenceError:wrong initial']
    while(1):
        F = comp(foo)
        if(F[0] == 'error'):
            return F
        if(not F[0]):
            break
        for i in block.split('\n')[1:-1]:
            i = i.strip()
            val = comp(i)
            if(val[0] == 'error'):
                return val
            if(status == MYL_BREAK_STATUS):
                status = MYL_NONE_STATUS
                return ['']
    return ['']

For status global variables, see
Chapter 2 of [Use python self-made programming language]

Parameters
block : code

At the beginning

    try:
        foo = block.split('\n')[0][6:-2]
    except:
        return ['error','WhileSentenceError:wrong initial']

To understand this, look at the syntax of for:

while(<foo>){
    <code>
}

Here block.split('\n')[0]is while(<foo>){ the line, 6: -2 is <foo>
therefore to beg <foo>used

later

    while(1):
        F = comp(foo)
        if(F[0] == 'error'):
            return F
        if(not F[0]):
            break
        for i in block.split('\n')[1:-1]:
            i = i.strip()
            val = comp(i)
            if(val[0] == 'error'):
                return val
            if(status == MYL_BREAK_STATUS):
                status = MYL_NONE_STATUS
                return ['']

Look separately

At the beginning

        F = comp(foo)
        if(F[0] == 'error'):
            return F
        if(not F[0]):
            break

Check expression<foo>

later

        for i in block.split('\n')[1:-1]:
            i = i.strip()
            val = comp(i)
            if(val[0] == 'error'):
                return val
            if(status == MYL_BREAK_STATUS):
                status = MYL_NONE_STATUS
                return ['']

Execute the code and judgebreak

At last

    return ['']

End

in conclusion

>> [Use python self-made programming language] Chapter 4

Author

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