Add matching and entry point code

src/Field.hs

@@ -16,11 +16,21 @@ data Field = Field Range Step
   deriving (Eq, Show)
 
 parseField :: String -> Constraint -> Maybe Field
-parseField text constraint
+parseField text constraint = parseField' (wordsWhen (== '/') text) constraint
+
+parseField' :: [String] -> Constraint -> Maybe Field
+parseField' [rangeText] constraint
   | isJust range = Just (Field (fromJust range) Every)
   | otherwise = Nothing
   where
-    range = parseFieldRange text constraint
+    range = parseFieldRange rangeText constraint
+parseField' [rangeText, stepText] constraint
+  | isJust range && isJust step = Just (Field (fromJust range) (fromJust step))
+  | otherwise = Nothing
+  where
+    range = parseFieldRange rangeText constraint
+    step = parseFieldStep stepText
+parseField' _ _ = Nothing
 
 parseFieldRange :: String -> Constraint -> Maybe Range
 parseFieldRange text constraint
@@ -76,3 +86,15 @@ parseFieldStep :: String -> Maybe Step
 parseFieldStep "" = Just Every
 parseFieldStep text | isNumber text = Just (Step (read text))
 parseFieldStep _ = Nothing
+
+matchField :: Field -> Int -> Bool
+matchField (Field range step) n = matchFieldRange range n && matchFieldStep step n
+
+matchFieldRange :: Range -> Int -> Bool
+matchFieldRange All _ = True
+matchFieldRange (Range x y) n = n >= x && n <= y
+matchFieldRange (Sequence xs) n = n `elem` xs
+
+matchFieldStep :: Step -> Int -> Bool
+matchFieldStep Every _ = True
+matchFieldStep (Step x) n = n `mod` x == 0

src/Pattern.hs

@@ -1,6 +1,7 @@
 module Pattern
     ( Pattern(..),
       match,
+      safeMatch,
       parse,
       check,
       createParts,
@@ -25,7 +26,7 @@ data Pattern = Pattern {
 match :: String -> DateTime -> Bool
 match s d =  case parse s of
     Just p -> check p d
-    Nothing -> error ""
+    Nothing -> error "Parse error"
 
 safeMatch :: String -> DateTime -> Maybe Bool
 safeMatch s d = case parse s of
@@ -81,7 +82,3 @@ check pattern date = all isRight pairs
                   (cyear pattern, year date)
                 ]
         isRight (pattern, value) = matchField pattern value
-
-matchField :: Field -> Int -> Bool
-matchField (Field All Every) _ = True
-matchField (Field (Range f t) Every) x = x >= f && x <= t