Merge pull request #58 from LiamGoodacre/feature/delimit

Add surroundMap and surround

Author: paf31

src/Data/Foldable.purs

@@ -7,6 +7,8 @@ module Data.Foldable
   , sequence_
   , oneOf
   , intercalate
+  , surroundMap
+  , surround
   , and
   , or
   , all
@@ -231,6 +233,47 @@ intercalate sep xs = (foldl go { init: true, acc: mempty } xs).acc
   go { init: true } x = { init: false, acc: x }
   go { acc: acc }   x = { init: false, acc: acc <> sep <> x }
 
+-- | `foldMap` but with each element surrounded by some fixed value.
+-- |
+-- | For example:
+-- |
+-- | ```purescript
+-- | > surroundMap "*" show []
+-- | = "*"
+-- |
+-- | > surroundMap "*" show [1]
+-- | = "*1*"
+-- |
+-- | > surroundMap "*" show [1, 2]
+-- | = "*1*2*"
+-- |
+-- | > surroundMap "*" show [1, 2, 3]
+-- | = "*1*2*3*"
+-- | ```
+surroundMap :: forall f a m. Foldable f => Semigroup m => m -> (a -> m) -> f a -> m
+surroundMap d t f = unwrap (foldMap joined f) d
+  where joined a = Endo \m -> d <> t a <> m
+
+-- | `fold` but with each element surrounded by some fixed value.
+-- |
+-- | For example:
+-- |
+-- | ```purescript
+-- | > surround "*" []
+-- | = "*"
+-- |
+-- | > surround "*" ["1"]
+-- | = "*1*"
+-- |
+-- | > surround "*" ["1", "2"]
+-- | = "*1*2*"
+-- |
+-- | > surround "*" ["1", "2", "3"]
+-- | = "*1*2*3*"
+-- | ```
+surround :: forall f m. Foldable f => Semigroup m => m -> f m -> m
+surround d = surroundMap d id
+
 -- | The conjunction of all the values in a data structure. When specialized
 -- | to `Boolean`, this function will test whether all of the values in a data
 -- | structure are `true`.

test/Main.purs

@@ -8,7 +8,7 @@ import Control.Monad.Eff.Console (CONSOLE, log)
 import Data.Bifoldable (class Bifoldable, bifoldl, bifoldr, bifoldMap, bifoldrDefault, bifoldlDefault, bifoldMapDefaultR, bifoldMapDefaultL)
 import Data.Bifunctor (class Bifunctor, bimap)
 import Data.Bitraversable (class Bitraversable, bisequenceDefault, bitraverse, bisequence, bitraverseDefault)
-import Data.Foldable (class Foldable, foldl, foldr, foldMap, foldrDefault, foldlDefault, foldMapDefaultR, foldMapDefaultL, minimumBy, minimum, maximumBy, maximum, find, findMap, length, null)
+import Data.Foldable (class Foldable, foldl, foldr, foldMap, foldrDefault, foldlDefault, foldMapDefaultR, foldMapDefaultL, minimumBy, minimum, maximumBy, maximum, find, findMap, length, null, surroundMap)
 import Data.Function (on)
 import Data.Int (toNumber)
 import Data.Maybe (Maybe(..))
@@ -117,6 +117,12 @@ main = do
   assert $ length [1] == 1
   assert $ length [1, 2] == 2
 
+  log "Test surroundMap"
+  assert $ "*" == surroundMap "*" show ([] :: Array Int)
+  assert $ "*1*" == surroundMap "*" show [1]
+  assert $ "*1*2*" == surroundMap "*" show [1, 2]
+  assert $ "*1*2*3*" == surroundMap "*" show [1, 2, 3]
+
   log "All done!"