types - Fixed size matrix and Maybe -


i writing board game in purescript involves matrix of exact size 2x7 (in variations can 4x7). package i’m using has matrix.getrow function returns maybe (array a).

what best approach not have deal maybe returns when know sure matrix.getrow 0 going return first row (because matrix of fixed size 2x7)?

currently have ugly code deal maybes not desirable:

notpossible :: array cell notpossible = [99, 99, 99, 99, 99, 99, 99]  -- never used  row n = frommaybe notpossible $ matrix.getrow n state.cells

purescript uses type system track partiality, partiality property function not produce return value possible inputs.

if want circumvent type system , guarantee not pass invalid inputs can use partial.unsafe.unsafepartial :: forall a. (partial => a) -> a function purescript-partial package.

by using partial function fromjust data.maybe

data.maybe.fromjust :: forall a. partial => maybe ->

you can construct unsafe row function:

unsaferow n xs = unsafepartial fromjust (matrix.getrow n xs)

you can delay calling unsafepartial point @ can guarantee index never out of bounds, type system propagate automatically you.


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