feat: add sepby1 combinator #165
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`sepby1` is a common reusable combinator in Haskell Parsec. This adds `mpc_sepby1(mpc_fold_t f, mpc_parser_t *sep, mpc_parser_t *a)` according to Haskell's implementation: https://hackage.haskell.org/package/parsec-3.1.16.1/docs/src/Text.Parsec.Combinator.html#sepBy1 Reuses existing `mpc_and`, `mpc_many`, and `mpcf_snd_free`.
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@HalosGhost @orangeduck How can I make it easier to get this reviewed? (It's a pretty short function and I've included tests/docs) |
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Looks great, thanks! |
| mpc_parser_t *mpc_sepby1(mpc_fold_t f, mpc_parser_t *sep, mpc_parser_t *a) { | ||
| return mpc_and(2, f, | ||
| a, mpc_many(f, mpc_and(2, mpcf_snd_free, sep, mpc_copy(a), free)), | ||
| free); | ||
| } |
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@orangeduck I've realized that the fold function is applied twice. This makes it hard (or maybe impossible) to build an array of structures with a custom fold function.
Do you have any advice on how to fix this?
Seems like we need a new repeat parser, but I'm lost on how to add those.
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I guess you mean that the fold function when used in mpc_many will get a list of entries, while when used in mpc_and it will just get the first item and the rest of the elements?
Yeah I see the problem.
The easiest thing would be to let people give two different fold functions to use in the mpc_and and the mpc_many.
There also might be a way to implement this in terms of mpc_many1 - in particular if you allow a trailing separator...
Otherwise I am not totally sure, and yes perhaps the only way is to implement a custom repeat parser type.
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@orangeduck Many thanks for the reply. I'm more familiar with the repeat parsers code now. I'm working on adding a new one for sepby1.
Preliminary work for that on #166.
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Thanks a lot for working on this addition 👍
Deduplicates the results allocation logic used in MPC_TYPE_MANY and MPC_TYPE_MANY1 on a `grow_results` function. This will aid in implementing new repeat parser types. A new one is neeeded for `sepby1` as discussed on orangeduck#165 (comment).
sepby1is a common reusable combinator in Haskell Parsec.This adds
mpc_sepby1(mpc_fold_t f, mpc_parser_t *sep, mpc_parser_t *a)according to Haskell's implementation:https://hackage.haskell.org/package/parsec-3.1.16.1/docs/src/Text.Parsec.Combinator.html#sepBy1
Reuses existing
mpc_and,mpc_many, andmpcf_snd_free.