Add Elem type family and ElemSym data type

[ashokkimmel]

Note, I did not test this.

[raehik]

The above two equations match both x:xs and [] cases, so this equation will never be reached. Also, did you intend to assert that x' and x are equivalent? In which case, it should be Elem (x:_) x = True.

[ashokkimmel]

I meant to do `Elem (x ': xs) x = 'True

[raehik]

Ahhh, of course. I tend to avoid ticked promoted constructors except where required to disambiguate. Further reading: https://gitlab.haskell.org/ghc/ghc/-/issues/20531

[raehik]

Thanks for this. I think this character predicate better fits with other parsers, which I hadn't implemented yet. I've done so at #5 :

type OneOf :: [Char] -> PParser Char
type OneOf chs = Satisfy (ElemSym chs)

So now you can say:

type ParseOperator = OneOf ['+', '-', '/', '*']

[raehik]

I'm considering this implemented. Note that I don't actually export my Elem type family or a defun symbol, because I consider them implementation details. (They should really be provided by a general-purpose type-level programming library. Symparsec relies on singleraeh, I should add them there. Eventually, haha...)

[ashokkimmel]

Thanks for this. I think this character predicate better fits with other parsers, which I hadn't implemented yet. I've done so at #5 :

type OneOf :: [Char] -> PParser Char
type OneOf chs = Satisfy (ElemSym chs)

So now you can say:

type ParseOperator = OneOf ['+', '-', '/', '*']

I was also thinking of a Not combinator, so you could do Not (OneOf ['-,'+','/','*']), or, if OneOf was changed to symbols: Not (OneOf "+-/*"). This would make it so that for Printf, you could just say While (Not (OneOf ['%']) and it would all work out.
I'm just trying to supply the barebones such that all files in Example don't need to mannually define App instances and can just use built in parser combinators. That's why I thought that adding Elem would be good. Want me to give more pull commits? I mainly use a chromebook (which is why I didn't test my code), but I have a PC with which I could clone the repo.

[raehik]

OneOf parses a Char. I think you mean something like Satisfy (Not (Elem chs)). megaparsec defines this as noneOf :: [Char] -> Parser Char. I'll add that.

I will gladly accept contributions. Can a Chromebook not run GHC? (GHC supports ARM64.)