[hs] Solve 2020_04

hs/src/Aoc/Parse.hs

@@ -4,10 +4,13 @@ module Aoc.Parse
   , module Text.Megaparsec.Char.Lexer
   , Parser
   , manyLines
+  , oneSpace
+  , untilSpace
   , untilEol
   , lineChar
   ) where
 
+import           Data.Char
 import           Data.Void
 
 import qualified Data.Text                  as T
@@ -22,8 +25,14 @@ type Parser = Parsec Void T.Text
 manyLines :: Parser a -> Parser [a]
 manyLines p = endBy (try p) newline
 
+oneSpace :: Parser Char
+oneSpace = label "whitespace character" $ satisfy isSpace
+
+untilSpace :: Parser T.Text
+untilSpace = takeWhileP (Just "non-whitespace character") (not . isSpace)
+
 untilEol :: Parser T.Text
-untilEol = takeWhileP Nothing (/= '\n')
+untilEol = takeWhileP (Just "non-newline character") (/= '\n')
 
 lineChar :: Parser Char
-lineChar = satisfy (/= '\n')
+lineChar = label "non-newline character" $ satisfy (/= '\n')