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use unreachable to implement walk

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Folkert 2022-07-03 03:01:23 +02:00
parent 762258ae20
commit 8a611fdb34
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13
crates/compiler/builtins/roc/List.roc
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@ -373,17 +373,12 @@ contains = \list, needle ->
## `fold`, `foldLeft`, or `foldl`.
walk : List elem, state, (state, elem -> state) -> state
walk = \list, state, func ->
walkHelp list state func 0 (len list)
walkHelp = \currentState, element -> Continue (func currentState element)
## internal helper
walkHelp : List elem, state, (state, elem -> state), Nat, Nat -> state
walkHelp = \list, state, f, index, length ->
if index < length then
nextState = f state (getUnsafe list index)
when List.iterate list state walkHelp is
Continue newState -> newState
Break void -> List.unreachable void
walkHelp list nextState f (index + 1) length
else
state
## Note that in other languages, `walkBackwards` is sometimes called `reduceRight`,
## `fold`, `foldRight`, or `foldr`.