1 files changed, 89 insertions, 0 deletions
diff --git a/src/nbc/parse-state.sml b/src/nbc/parse-state.sml
new file mode 100644
index 0000000..8b30a67
--- /dev/null
+++ b/src/nbc/parse-state.sml
@@ -0,0 +1,89 @@
+signature PARSE_STATE = sig
+	type ('argument, 'result) state
+	val create: unit -> ('argument, 'result) state
+	type ('argument, 'result) handler =
+		TextIO.instream * 'argument -> 'result
+	datatype whichCharacters = These of char list | Any
+	val build: {
+		state: ('argument, 'result) state
+		, characters:
+			(whichCharacters * ('argument, 'result) handler) list
+		, endOfFile: ('argument, 'result) handler
+	} -> unit
+	val enter:
+		('argument, 'result) state
+			* TextIO.instream
+			* 'argument
+		-> 'result
+end
+
+structure ParseState :> PARSE_STATE = struct
+	type ('argument, 'result) handler =
+		TextIO.instream * 'argument -> 'result
+	datatype whichCharacters = These of char list | Any
+	type ('argument, 'result) state = {
+		byCharacter: Int8.int vector ref
+		, byIndex: ('argument, 'result) handler vector ref
+		, endOfFile: ('argument, 'result) handler option ref
+	}
+	fun create () = {
+		byCharacter = ref (Vector.fromList nil)
+		, byIndex = ref (Vector.fromList nil)
+		, endOfFile = ref NONE
+	}
+	fun build {
+		state = {byCharacter, byIndex, endOfFile}
+		, characters
+		, endOfFile = newEndOfFile
+	} =
+		let
+			val characters = vector characters
+			fun equal (one: char) (two: char) =
+				one = two
+			fun shallHandle ((whichToHandle, _), char) =
+				case whichToHandle of
+					Any => true
+					| These charactersToHandle =>
+						List.exists (equal char)
+							charactersToHandle
+			fun charToIndex char =
+				case
+					Vector.findi (fn (_, handler) =>
+						shallHandle (handler, char)
+					) characters
+				of
+					NONE => raise Fail (
+						"ParseState.build: "
+						^ Char.toString char
+						^ " not found"
+					) | SOME (index, _) =>
+						Int8.fromInt index
+			fun handlerToFunction (_, function) = function
+			fun indexToFunction index = handlerToFunction (
+				Vector.sub (characters, index)
+			)
+		in
+			byCharacter := Vector.tabulate (
+				Char.maxOrd + 1
+				, charToIndex o chr
+			); byIndex :=
+				Vector.map (fn (_, function) =>
+					function
+				) characters
+			; endOfFile := SOME newEndOfFile
+		end
+	fun enter (
+		{
+			byCharacter = ref byCharacter
+			, byIndex = ref byIndex
+			, endOfFile = ref endOfFile
+		}
+		, instream
+		, argument
+	) = case TextIO.input1 instream of
+		NONE => (valOf endOfFile) (instream, argument)
+		| SOME char => Vector.sub (
+			byIndex
+			, Int8.toInt (Vector.sub (byCharacter, ord char))
+		) (instream, argument)
+end