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Fix traverse failing at runtime #2

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Fix traverse failing at runtime #2

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6607e57
Use correct Semigroup.append instead table.concat
Renegatto Oct 25, 2025
c129cb5
Fix: consider array indexing starting from 1 in lua
Renegatto Oct 25, 2025
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39 changes: 20 additions & 19 deletions src/Data/Traversable.lua
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Original file line number Diff line number Diff line change
@@ -1,31 +1,32 @@
local array1 = function(a) return {a} end
local array2 = function(a) return function(b) return {a, b} end end
local array3 = function(a) return function(b) return function(c) return {a, b, c} end end end
local concat2 = function(xs) return function(ys) return table.concat(xs, ys) end end
return {
traverseArrayImpl = (function(apply)
return function(map)
return function(pure)
return function(f)
return function(array)
local function go(bot, top)
if top - bot == 0 then
return pure({})
elseif top - bot == 1 then
return map(array1)(f(array[bot]))
elseif top - bot == 2 then
return apply(map(array2)(f(array[bot])))(f(array[bot + 1]))
elseif top - bot == 3 then
return apply(apply(map(array3)(f(array[bot])))(f(array[bot + 1])))(f(array[bot + 2]))
else
-- This slightly tricky pivot selection aims to produce two
-- even-length partitions where possible.
local pivot = bot + math.floor((top - bot) / 4) * 2
return apply(map(concat2)(go(bot, pivot)))(go(pivot, top))
return function (appendArrays)
return function(f)
return function(array)
local function go(bot, top)
if top - bot == 0 then
return pure({})
elseif top - bot == 1 then
return map(array1)(f(array[bot + 1]))
elseif top - bot == 2 then
return apply(map(array2)(f(array[bot + 1])))(f(array[bot + 2]))
elseif top - bot == 3 then
return apply(apply(map(array3)(f(array[bot + 1])))(f(array[bot + 2])))(f(array[bot + 3]))
else
-- This slightly tricky pivot selection aims to produce two
-- even-length partitions where possible.
local pivot = bot + math.floor((top - bot) / 4) * 2
return apply(map(appendArrays)(go(bot, pivot)))(go(pivot, top))
end
end
end

return go(0, #array)
return go(0, #array)
end
end
end
end
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3 changes: 2 additions & 1 deletion src/Data/Traversable.purs
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Original file line number Diff line number Diff line change
Expand Up @@ -100,14 +100,15 @@ sequenceDefault
sequenceDefault = traverse identity

instance traversableArray :: Traversable Array where
traverse = traverseArrayImpl apply map pure
traverse = traverseArrayImpl apply map pure (<>)
sequence = sequenceDefault

foreign import traverseArrayImpl
:: forall m a b
. (forall x y. m (x -> y) -> m x -> m y)
-> (forall x y. (x -> y) -> m x -> m y)
-> (forall x. x -> m x)
-> (forall x. Array x -> Array x -> Array x)
-> (a -> m b)
-> Array a
-> m (Array b)
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