Add concatMapSep (#75)

Prelude/Text/concatMapSep

@@ -0,0 +1,47 @@
+{-
+Transform each value in a `List` to `Text` and then concatenate them with a
+separator in between each value
+
+Examples:
+
+```
+./concatMapSep ", " Integer Integer/show [0, 1, 2] = "0, 1, 2"
+
+./concatMapSep ", " Integer Integer/show ([] : List Integer) = ""
+```
+-}
+let concatMapSep
+    :   ∀(separator : Text) → ∀(a : Type) → (a → Text) → List a → Text
+    =   λ(separator : Text)
+    →   λ(a : Type)
+    →   λ(f : a → Text)
+    →   λ(elements : List a)
+    →   let status
+            =   List/fold
+                a
+                elements
+                < Empty : {} | NonEmpty : Text >
+                (   λ(element : a)
+                →   λ(status : < Empty : {} | NonEmpty : Text >)
+                →   merge
+                    {   Empty
+                        =   λ(_ : {})
+                        →   < NonEmpty = f element
+                            | Empty : {}
+                            >
+                    ,   NonEmpty
+                        =   λ(result : Text)
+                        →   < NonEmpty = f element ++ separator ++ result
+                            | Empty : {}
+                            >
+                    }
+                    status : < Empty : {} | NonEmpty : Text >
+                )
+                < Empty = {=} | NonEmpty : Text >
+    in  merge
+        { Empty    = λ(_ : {}) → ""
+        , NonEmpty = λ(result : Text) → result
+        }
+        status : Text
+
+in  concatMapSep

tests/Examples.hs

@@ -240,6 +240,10 @@ exampleTests =
                 [ _Text_concatSep_0
                 , _Text_concatSep_1
                 ]
+            , Test.Tasty.testGroup "concatMapSep"
+                [ _Text_concatMapSep_0
+                , _Text_concatMapSep_1
+                ]
             ]
         ]
 
@@ -1152,3 +1156,17 @@ _Text_concatSep_1 = Test.Tasty.HUnit.testCase "Example #1" (do
 ./Prelude/Text/concatSep ", " ([] : List Text)
 |]
     Util.assertNormalizesTo e "\"\"" )
+
+_Text_concatMapSep_0 :: TestTree
+_Text_concatMapSep_0 = Test.Tasty.HUnit.testCase "Example #0" (do
+    e <- Util.code [NeatInterpolation.text|
+./Prelude/Text/concatMapSep ", " Integer Integer/show [0, 1, 2]
+|]
+    Util.assertNormalizesTo e "\"0, 1, 2\"" )
+
+_Text_concatMapSep_1 :: TestTree
+_Text_concatMapSep_1 = Test.Tasty.HUnit.testCase "Example #1" (do
+    e <- Util.code [NeatInterpolation.text|
+./Prelude/Text/concatMapSep ", " Integer Integer/show ([] : List Integer)
+|]
+    Util.assertNormalizesTo e "\"\"" )