Added digitToInt function.

Author: cdepillabout

src/Data/Char/Unicode.purs

@@ -514,19 +514,23 @@ toTitle = fromCharCode <<< uTowtitle <<< toCharCode
 -- | >>> digitToInt '♥'
 -- | *** Exception: Char.digitToInt: not a digit '\9829'
 -- | ```
--- |
--- | TODO: This function.
--- |
--- digitToInt :: Char -> Int
--- digitToInt c
---   | (fromIntegral dec::Word) <= 9 = dec
---   | (fromIntegral hexl::Word) <= 5 = hexl + 10
---   | (fromIntegral hexu::Word) <= 5 = hexu + 10
---   | otherwise = errorWithoutStackTrace ("Char.digitToInt: not a digit " ++ show c) -- sigh
---   where
---     dec = ord c - ord '0'
---     hexl = ord c - ord 'a'
---     hexu = ord c - ord 'A'
+digitToInt :: Char -> Maybe Int
+digitToInt c = go c
+  where
+    go :: Char -> Maybe Int
+    go c | dec      <= 9 && dec      >= 0 = Just dec
+         | hexLower <= 5 && hexLower >= 0 = Just $ hexLower + 10
+         | hexUpper <= 5 && hexUpper >= 0 = Just $ hexUpper + 10
+         | otherwise                      = Nothing
+
+    dec :: Int
+    dec = toCharCode c - toCharCode '0'
+
+    hexLower :: Int
+    hexLower = toCharCode c - toCharCode 'a'
+
+    hexUpper :: Int
+    hexUpper = toCharCode c - toCharCode 'A'
 
 -- | Selects alphabetic Unicode characters (lower-case, upper-case and
 -- | title-case letters, plus letters of caseless scripts and

test/Test/Data/Char/Unicode.purs

@@ -37,6 +37,7 @@ dataCharUnicodeTests = describe "module Data.Char.Unicode" do
     toUpperTests
     toLowerTests
     toTitleTests
+    digitToIntTests
     isLetterTests
     isMarkTests
     isNumberTests
@@ -321,6 +322,24 @@ toLowerTests = pure unit
 toTitleTests :: forall eff . Spec eff Unit
 toTitleTests = pure unit
 
+digitToIntTests :: forall eff . Spec eff Unit
+digitToIntTests = describe "digitToInt" do
+    it "'0'..'9' get mapped correctly" $
+        map digitToInt ['0','1','2','3','4','5','6','7','8','9'] `shouldEqual`
+            [Just 0, Just 1, Just 2, Just 3, Just 4, Just 5, Just 6, Just 7, Just 8, Just 9]
+    it "'a'..'f' get mapped correctly" $
+        map digitToInt ['a','b','c','d','e','f'] `shouldEqual`
+            [Just 10, Just 11, Just 12, Just 13, Just 14, Just 15]
+    it "'A'..'F' get mapped correctly" $
+        map digitToInt ['A','B','C','D','E','F'] `shouldEqual`
+            [Just 10, Just 11, Just 12, Just 13, Just 14, Just 15]
+    it "'G' is not a digit" $
+        digitToInt 'G' `shouldEqual` Nothing
+    it "'♥' is not a digit" $
+        digitToInt '♥' `shouldEqual` Nothing
+    it "'国' is not a digit" $
+        digitToInt '国' `shouldEqual` Nothing
+
 isLetterTests:: forall eff . Spec (console :: CONSOLE, random :: RANDOM, err :: EXCEPTION | eff) Unit
 isLetterTests = describe "isLetter" do
     prop "isLetter == isAlpha" \char -> isLetter char == isAlpha char