Add RNA Transcription exercise

config.json

@@ -273,6 +273,17 @@
         "arrays",
         "modulo"
       ]
+    },
+    {
+      "uuid": "8ebcfe11-0a42-e980-d120-fb3fd581e426e9e237e",
+      "slug": "rna-transcription",
+      "core": false,
+      "unlocked_by": null,
+      "difficulty": 1,
+      "topics": [
+        "maybe",
+        "strings"
+      ]
     }
   ],
   "foregone": [

exercises/rna-transcription/README.md

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+# Rna Transcription
+
+Given a DNA strand, return its RNA complement (per RNA transcription).
+
+Both DNA and RNA strands are a sequence of nucleotides.
+
+The four nucleotides found in DNA are adenine (**A**), cytosine (**C**),
+guanine (**G**) and thymine (**T**).
+
+The four nucleotides found in RNA are adenine (**A**), cytosine (**C**),
+guanine (**G**) and uracil (**U**).
+
+Given a DNA strand, its transcribed RNA strand is formed by replacing
+each nucleotide with its complement:
+
+* `G` -> `C`
+* `C` -> `G`
+* `T` -> `A`
+* `A` -> `U`
+## Source
+
+Rosalind [http://rosalind.info/problems/rna](http://rosalind.info/problems/rna)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/rna-transcription/bower.json

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+{
+  "name": "rna-transcription",
+  "ignore": [
+    "**/.*",
+    "node_modules",
+    "bower_components",
+    "output"
+  ],
+  "dependencies": {
+    "purescript-console": "^3.0.0",
+    "purescript-datetime": "^3.4.0",
+    "purescript-either": "^3.1.0",
+    "purescript-enums": "^3.2.1",
+    "purescript-integers": "^3.1.0",
+    "purescript-lists": "^4.10.0",
+    "purescript-maps": "^3.5.2",
+    "purescript-prelude": "^3.1.0",
+    "purescript-sets": "^3.0.0",
+    "purescript-strings": "^3.3.1",
+    "purescript-unicode": "^3.0.1"
+  },
+  "devDependencies": {
+    "purescript-psci-support": "^3.0.0",
+    "purescript-test-unit": "^13.0.0"
+  }
+}

exercises/rna-transcription/examples/src/RNATranscription.purs

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+module RNATranscription
+  ( toRNA
+  ) where
+
+import Prelude
+import Data.Maybe (Maybe(..))
+import Data.String (fromCharArray, toCharArray)
+import Data.Traversable (traverse)
+
+toRNA :: String -> Maybe String
+toRNA dna = fromCharArray <$> traverse complement (toCharArray dna)
+
+complement :: Char -> Maybe Char
+complement 'C' = Just 'G'
+complement 'G' = Just 'C'
+complement 'A' = Just 'U'
+complement 'T' = Just 'A'
+complement _ = Nothing

exercises/rna-transcription/src/RNATranscription.purs

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+module RNATranscription
+  ( toRNA
+  ) where

exercises/rna-transcription/test/Main.purs

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+module Test.Main where
+
+import Prelude
+import Control.Monad.Eff (Eff)
+import Control.Monad.Eff.AVar (AVAR)
+import Control.Monad.Eff.Console (CONSOLE)
+import Data.Maybe (Maybe(..))
+import Test.Unit (TestSuite, suite, test)
+import Test.Unit.Assert as Assert
+import Test.Unit.Console (TESTOUTPUT)
+import Test.Unit.Main (runTest)
+import RNATranscription (toRNA)
+
+main :: forall eff
+  . Eff ( avar :: AVAR
+        , console :: CONSOLE
+        , testOutput :: TESTOUTPUT
+        | eff
+        )
+        Unit
+main = runTest suites
+
+suites :: forall e. TestSuite e
+suites =
+  suite "RNATranscription.toRNA" do
+    test "RNA complement of cytosine is guanine" $
+      Assert.equal (Just "G") (toRNA "C")
+
+    test "RNA complement of guanine is cytosine" $
+      Assert.equal (Just "C") (toRNA "G")
+
+    test "RNA complement of thymine is adenine" $
+      Assert.equal (Just "A") (toRNA "T")
+
+    test "RNA complement of adenine is uracil" $
+      Assert.equal (Just "U") (toRNA "A")
+
+    test "RNA complement" $
+      Assert.equal (Just "UGCACCAGAAUU") (toRNA "ACGTGGTCTTAA")
+
+    test "correctly handles invalid input (RNA instead of DNA)" $
+      Assert.equal Nothing (toRNA "U")
+
+    test "correctly handles completely invalid DNA input" $
+      Assert.equal Nothing (toRNA "XXX")
+
+    test "correctly handles partially invalid DNA input" $
+      Assert.equal Nothing (toRNA "ACGTXXXCTTAA")