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manyMonoid? #220

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jamesdbrock opened this issue Dec 10, 2022 · 0 comments

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jamesdbrock commented Dec 10, 2022

https://discord.com/channels/864614189094928394/865401680497737758/1050733797278228500

@artemisSystem
is there a combinator in parsing that works like many but accumulates in an arbitrary monoid?

like this:
manyMonoid ∷ ∀ s a. Monoid a ⇒ Parser s a → Parser s a
manyMonoid = many >>> map fold

manyMonoid p = tailRecM go empty
where
go accum = alt
  do
    x <- p
    pure (Loop (accum <> x))
  do
    pure (Done accum)

See also https://pursuit.purescript.org/packages/purescript-arrays/7.1.0/docs/Data.Array#v:foldRecM

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