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Increment and decrement operators result in parse error #190

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TwitchBronBron opened this issue Mar 9, 2019 · 0 comments · Fixed by #222
Closed

Increment and decrement operators result in parse error #190

TwitchBronBron opened this issue Mar 9, 2019 · 0 comments · Fixed by #222
Labels
bug Any difference between this BrightScript implementation and RBI, or otherwise unexpected behavior interpreter Affects this project's tree-walking interpreter lexer Affects this project's lexer (aka scanner) parser Affects this project's token parser

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@TwitchBronBron
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The increment and decrement operators do not seem to be supported, and result in a parse error.
image


sub Main()
    age = 1
    age++
    age--
    person = {
        age: 10
    }
    person.age++
    person.age--
end sub

Roku docs
@sjbarag sjbarag added bug Any difference between this BrightScript implementation and RBI, or otherwise unexpected behavior lexer Affects this project's lexer (aka scanner) parser Affects this project's token parser interpreter Affects this project's tree-walking interpreter labels Mar 9, 2019
@sjbarag sjbarag mentioned this issue Apr 28, 2019
Merged
sjbarag added a commit that referenced this issue Apr 29, 2019
@sjbarag
feat(lex,parse,interp): Implement ++ and -- operators (#222)
ab852e3 
It's finally here: support for `++` and `--`!

A few things to note for anyone reading this:

1. This is still mostly a nights-and-weekends project, in which I work
   on it when I have some free time.  I haven't had much lately, hence
   the delay in getting this out to the world.
2. This could have been implemented as syntactic sugar, in that a
   `foo++` statement is expanded to `foo = foo + 1`, and I in fact
   started that way!  Eventually I chose to make `++`/`--` top-level
   statements.  This allows for much more clear error messaging, and
   makes the parsing rules a bit more explicit as well.  It seems better
   for everyone this way :)
3. The Reference BrightScript Implementation only allows `++` and `--`
   to exist as a statement — *not* as an expression!  That means the
   following contrived uses are not syntactically valid:

```brightscript
sub countToFive()
    i = 0
    while i++ < 5
'         ~~~
'         ++ can't be used as part of the binary expression `A < B`
        print i
    end while

    print "Stopped at " i++
'                       ~~~
'                       print statements accept a list of expressions,
'                       not statements
end sub
```

Compare this to JavaScript, Java, C, etc., in which the `++` and `--`
operators can be used basically anywhere an expression is used, e.g.:

```javascript
function countToFive() {
    let i = 0;
    while (i++ < 5) {
        console.log(i);
    }

    console.log(`Stopped at ${i++}`);
}
```

fixes #190
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bug Any difference between this BrightScript implementation and RBI, or otherwise unexpected behavior interpreter Affects this project's tree-walking interpreter lexer Affects this project's lexer (aka scanner) parser Affects this project's token parser
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feat(lex,parse,interp): Implement ++ and -- operators sjbarag/brs
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@sjbarag @TwitchBronBron