made interface of ‘Text.Megaparsec.Pos’ smarter

Now it's impossible to create ‘SourcePos’ with non-positive line number
or column number. Unfortunately we cannot use ‘Numeric.Natural’ because
we need to support older versions of ‘base’.

CHANGELOG.md

@@ -1,3 +1,10 @@
+## Megaparsec 4.2.0
+
+* Made `newPos` constructor and other functions in `Text.Megaparsec.Pos`
+  smarter. Now it's impossible to create `SourcePos` with non-positive line
+  number or column number. Unfortunately we cannot use `Numeric.Natural`
+  because we need to support older versions of `base`.
+
 ## Megaparsec 4.1.1
 
 * Fixed bug in implementation of `sepEndBy` and `sepEndBy1` and removed

Text/Megaparsec/Pos.hs

@@ -28,9 +28,7 @@ module Text.Megaparsec.Pos
   , defaultTabWidth )
 where
 
-import Data.Data (Data)
 import Data.List (foldl')
-import Data.Typeable (Typeable)
 
 -- | The abstract data type @SourcePos@ represents source positions. It
 -- contains the name of the source (i.e. file name), a line number and a
@@ -44,7 +42,7 @@ data SourcePos = SourcePos
   , sourceLine   :: !Int
     -- | Extract the column number from a source position.
   , sourceColumn :: !Int }
-  deriving (Eq, Ord, Data, Typeable)
+  deriving (Eq, Ord)
 
 instance Show SourcePos where
   show (SourcePos n l c)
@@ -54,9 +52,12 @@ instance Show SourcePos where
 
 -- | Create a new 'SourcePos' with the given source name, line number and
 -- column number.
+--
+-- In call @newPos name line column@, if @line@ is not a positive
+-- number, 1 will be used. The same holds for @column@ value.
 
 newPos :: String -> Int -> Int -> SourcePos
-newPos = SourcePos
+newPos n l c = SourcePos n (max 1 l) (max 1 c)
 
 -- | Create a new 'SourcePos' with the given source name, and line number
 -- and column number set to 1, the upper left.
@@ -64,30 +65,34 @@ newPos = SourcePos
 initialPos :: String -> SourcePos
 initialPos name = newPos name 1 1
 
--- | Increment the line number of a source position.
+-- | Increment the line number of a source position. If resulting line
+-- number is not positive, line number will be equal to 1.
 
 incSourceLine :: SourcePos -> Int -> SourcePos
-incSourceLine (SourcePos n l c) d = SourcePos n (l + d) c
+incSourceLine (SourcePos n l c) d = SourcePos n (max 1 $ l + d) c
 
--- | Increments the column number of a source position.
+-- | Increments the column number of a source position. If resulting column
+-- number is not positive, column number will be equal to 1.
 
 incSourceColumn :: SourcePos -> Int -> SourcePos
-incSourceColumn (SourcePos n l c) d = SourcePos n l (c + d)
+incSourceColumn (SourcePos n l c) d = SourcePos n l (max 1 $ c + d)
 
 -- | Set the name of the source.
 
 setSourceName :: SourcePos -> String -> SourcePos
 setSourceName (SourcePos _ l c) n = SourcePos n l c
 
--- | Set the line number of a source position.
+-- | Set the line number of a source position. If the line number is not
+-- positive, 1 will be used.
 
 setSourceLine :: SourcePos -> Int -> SourcePos
-setSourceLine (SourcePos n _ c) l = SourcePos n l c
+setSourceLine (SourcePos n _ c) l = SourcePos n (max 1 l) c
 
--- | Set the column number of a source position.
+-- | Set the column number of a source position. If the line number is not
+-- positive, 1 will be used.
 
 setSourceColumn :: SourcePos -> Int -> SourcePos
-setSourceColumn (SourcePos n l _) = SourcePos n l
+setSourceColumn (SourcePos n l _) c = SourcePos n l (max 1 c)
 
 -- | Update a source position given a character. The first argument
 -- specifies tab width. If the character is a newline (\'\\n\') the line

tests/Pos.hs

@@ -47,6 +47,7 @@ import Control.Applicative ((<$>), (<*>), pure)
 tests :: Test
 tests = testGroup "Textual source positions"
         [ testProperty "components" prop_components
+        , testProperty "positive coordinates" prop_positive
         , testProperty "show file name in source positions" prop_showFileName
         , testProperty "show line in source positions" prop_showLine
         , testProperty "show column in source positions" prop_showColumn
@@ -59,7 +60,7 @@ tests = testGroup "Textual source positions"
         , testProperty "position updating" prop_updating ]
 
 instance Arbitrary SourcePos where
-  arbitrary = newPos <$> fileName <*> choose (1, 1000) <*> choose (0, 100)
+  arbitrary = newPos <$> fileName <*> choose (-10, 1000) <*> choose (-10, 100)
 
 fileName :: Gen String
 fileName = do
@@ -74,6 +75,9 @@ prop_components :: SourcePos -> Bool
 prop_components pos = pos == copy
   where copy = newPos (sourceName pos) (sourceLine pos) (sourceColumn pos)
 
+prop_positive :: SourcePos -> Bool
+prop_positive pos = sourceLine pos > 0 && sourceColumn pos > 0
+
 prop_showFileName :: SourcePos -> Bool
 prop_showFileName pos = sourceName pos `isInfixOf` show pos
 
@@ -90,21 +94,21 @@ prop_initialPos n =
   sourceColumn ipos == 1
   where ipos = initialPos n
 
-prop_incSourceLine :: SourcePos -> NonNegative Int -> Bool
+prop_incSourceLine :: SourcePos -> Int -> Bool
 prop_incSourceLine pos l =
-  d sourceName   id     pos incp &&
-  d sourceLine   (+ l') pos incp &&
-  d sourceColumn id     pos incp
-  where l'   = getNonNegative l
-        incp = incSourceLine pos l'
+  d sourceName   id pos incp &&
+  d sourceLine   f  pos incp &&
+  d sourceColumn id pos incp
+  where f    = max 1 . (+ l)
+        incp = incSourceLine pos l
 
-prop_incSourceColumn :: SourcePos -> NonNegative Int -> Bool
+prop_incSourceColumn :: SourcePos -> Int -> Bool
 prop_incSourceColumn pos c =
-  d sourceName   id     pos incp &&
-  d sourceLine   id     pos incp &&
-  d sourceColumn (+ c') pos incp
-  where c'   = getNonNegative c
-        incp = incSourceColumn pos c'
+  d sourceName   id pos incp &&
+  d sourceLine   id pos incp &&
+  d sourceColumn f  pos incp
+  where f    = max 1 . (+ c)
+        incp = incSourceColumn pos c
 
 prop_setSourceName :: SourcePos -> String -> Bool
 prop_setSourceName pos n =
@@ -113,21 +117,21 @@ prop_setSourceName pos n =
   d sourceColumn id        pos setp
   where setp = setSourceName pos n
 
-prop_setSourceLine :: SourcePos -> Positive Int -> Bool
+prop_setSourceLine :: SourcePos -> Int -> Bool
 prop_setSourceLine pos l =
   d sourceName   id         pos setp &&
   d sourceLine   (const l') pos setp &&
   d sourceColumn id         pos setp
-  where l'   = getPositive l
-        setp = setSourceLine pos l'
+  where l'   = max 1 l
+        setp = setSourceLine pos l
 
-prop_setSourceColumn :: SourcePos -> NonNegative Int -> Bool
+prop_setSourceColumn :: SourcePos -> Int -> Bool
 prop_setSourceColumn pos c =
   d sourceName   id         pos setp &&
   d sourceLine   id         pos setp &&
   d sourceColumn (const c') pos setp
-  where c'   = getNonNegative c
-        setp = setSourceColumn pos c'
+  where c'   = max 1 c
+        setp = setSourceColumn pos c
 
 prop_updating :: Int -> SourcePos -> String -> Bool
 prop_updating w pos "" = updatePosString w pos "" == pos