Add initState and initPosState to Text.Megaparsec.State

CHANGELOG.md

@@ -1,5 +1,11 @@
 *Megaparsec follows [SemVer](https://semver.org/).*
 
+## Unreleased
+
+* Added the functions `initialState` and `initialPosState` to
+  `Text.Megaparsec.State`. [Issue
+  449](https://github.com/mrkkrp/megaparsec/issues/449).
+
 ## Megaparsec 9.5.0
 
 * Dropped a number of redundant constraints here and there. [PR

Text/Megaparsec.hs

@@ -295,24 +295,6 @@ runParserT' p s = do
     Error e ->
       (s', Left (toBundle (e :| stateParseErrors s')))
 
--- | Given the name of source file and the input construct the initial state
--- for a parser.
-initialState :: String -> s -> State s e
-initialState name s =
-  State
-    { stateInput = s,
-      stateOffset = 0,
-      statePosState =
-        PosState
-          { pstateInput = s,
-            pstateOffset = 0,
-            pstateSourcePos = initialPos name,
-            pstateTabWidth = defaultTabWidth,
-            pstateLinePrefix = ""
-          },
-      stateParseErrors = []
-    }
-
 ----------------------------------------------------------------------------
 -- Signaling parse errors
 

Text/Megaparsec/State.hs

@@ -21,7 +21,9 @@
 -- @since 6.5.0
 module Text.Megaparsec.State
   ( State (..),
+    initialState,
     PosState (..),
+    initialPosState,
   )
 where
 
@@ -74,6 +76,24 @@ deriving instance
 
 instance (NFData s, NFData (ParseError s e)) => NFData (State s e)
 
+-- | Given the name of the source file and the input construct the initial
+-- state for a parser.
+--
+-- @since 9.6.0
+initialState ::
+  -- | Name of the file the input is coming from
+  FilePath ->
+  -- | Input
+  s ->
+  State s e
+initialState name s =
+  State
+    { stateInput = s,
+      stateOffset = 0,
+      statePosState = initialPosState name s,
+      stateParseErrors = []
+    }
+
 -- | A special kind of state that is used to calculate line\/column
 -- positions on demand.
 --
@@ -93,3 +113,22 @@ data PosState s = PosState
   deriving (Show, Eq, Data, Typeable, Generic)
 
 instance (NFData s) => NFData (PosState s)
+
+-- | Given the name of source file and the input construct the initial
+-- positional state.
+--
+-- @since 9.6.0
+initialPosState ::
+  -- | Name of the file the input is coming from
+  String ->
+  -- | Input
+  s ->
+  PosState s
+initialPosState name s =
+  PosState
+    { pstateInput = s,
+      pstateOffset = 0,
+      pstateSourcePos = initialPos name,
+      pstateTabWidth = defaultTabWidth,
+      pstateLinePrefix = ""
+    }