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Merged
paf31 merged 2 commits into from
Nov 2, 2016
+10 −12
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Safe traverse, fix #86 #87

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f4acf68
Safe traverse, fix #86
paf31 Nov 1, 2016
9827806
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paf31 Nov 2, 2016
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11 changes: 4 additions & 7 deletions src/Data/List/Types.purs
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Original file line number Diff line number Diff line change
@@ -1,23 +1,22 @@
module Data.List.Types where

import Prelude

import Control.Alt (class Alt)
import Control.Alternative (class Alternative)
import Control.Apply (lift2)
import Control.Comonad (class Comonad)
import Control.Extend (class Extend)
import Control.MonadPlus (class MonadPlus)
import Control.MonadZero (class MonadZero)
import Control.Plus (class Plus)

import Data.Foldable (class Foldable, foldr, foldl, intercalate)
import Data.Generic (class Generic)
import Data.Maybe (Maybe(..))
import Data.Monoid (class Monoid, mempty)
import Data.Newtype (class Newtype)
import Data.NonEmpty (NonEmpty, (:|))
import Data.NonEmpty as NE
import Data.Traversable (class Traversable, traverse, sequence)
import Data.Traversable (class Traversable, traverse)
import Data.Tuple (Tuple(..))
import Data.Unfoldable (class Unfoldable)

Expand Down Expand Up @@ -79,10 +78,8 @@ instance unfoldableList :: Unfoldable List where
Just (Tuple one rest) -> go rest (one : memo)

instance traversableList :: Traversable List where
traverse _ Nil = pure Nil
traverse f (a : as) = Cons <$> f a <*> traverse f as
sequence Nil = pure Nil
sequence (a : as) = Cons <$> a <*> sequence as
traverse f = map (foldl (flip (:)) Nil) <<< foldl (\acc -> lift2 (flip (:)) acc <<< f) (pure Nil)
sequence = traverse id

instance applyList :: Apply List where
apply Nil _ = Nil
Expand Down
11 changes: 6 additions & 5 deletions test/Test/Data/List.purs
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Original file line number Diff line number Diff line change
@@ -1,21 +1,18 @@
module Test.Data.List (testList) where

import Prelude

import Data.List.NonEmpty as NEL
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Console (CONSOLE, log)

import Data.Foldable (foldMap, foldl)
import Data.List (List(..), (..), length, range, foldM, unzip, zip, zipWithA, zipWith, intersectBy, intersect, (\\), deleteBy, delete, unionBy, union, nubBy, nub, groupBy, group', group, span, dropWhile, drop, takeWhile, take, sortBy, sort, catMaybes, mapMaybe, filterM, filter, concat, concatMap, reverse, alterAt, modifyAt, updateAt, deleteAt, insertAt, findLastIndex, findIndex, elemLastIndex, elemIndex, (!!), uncons, init, tail, last, head, insertBy, insert, snoc, null, singleton, fromFoldable, transpose, mapWithIndex, (:))
import Data.List.NonEmpty as NEL
import Data.Maybe (Maybe(..), isNothing, fromJust)
import Data.Monoid.Additive (Additive(..))
import Data.NonEmpty ((:|))
import Data.Traversable (traverse)
import Data.Tuple (Tuple(..))
import Data.Unfoldable (replicate, replicateA, unfoldr)

import Partial.Unsafe (unsafePartial)

import Test.Assert (ASSERT, assert)

testList :: forall eff. Eff (assert :: ASSERT, console :: CONSOLE | eff) Unit
Expand Down Expand Up @@ -318,6 +315,10 @@ testList = do
log "transpose (singleton Nil) == Nil"
assert $ transpose (singleton Nil) == (Nil :: List (List Int))

log "traverse should be stack-safe"
let xs = fromFoldable (range 1 100000)
assert $ traverse Just xs == Just xs

step :: Int -> Maybe (Tuple Int Int)
step 6 = Nothing
step n = Just (Tuple n (n + 1))
Expand Down