From 8943da5aeeefb0db7775837dbfea729d75cc8434 Mon Sep 17 00:00:00 2001
From: Brandon Dyck <brandon@dyck.us>
Date: Mon, 9 Sep 2024 15:00:17 -0600
Subject: [PATCH] Check that Slice has correct position after matching

---
 gigaparsec.go  | 23 ++++++++++-------------
 parser_test.go | 23 ++++++++++++++++-------
 2 files changed, 26 insertions(+), 20 deletions(-)

diff --git a/gigaparsec.go b/gigaparsec.go
index 2f734fb..874f7a3 100644
--- a/gigaparsec.go
+++ b/gigaparsec.go
@@ -31,30 +31,27 @@ func (pe ParseError) Error() string {
 	return fmt.Sprintf("parse error: %d: %s", pe.Pos, pe.Got)
 }
 
-type State[T any] struct {
-	cursor cursor.Cursor[T]
+func MakeState[In any](c cursor.Cursor[In]) State[In] {
+	return State[In]{cursor: c}
 }
 
-func (s State[T]) Cursor() cursor.Cursor[T] {
+type State[In any] struct {
+	cursor cursor.Cursor[In]
+}
+
+func (s State[In]) Cursor() cursor.Cursor[In] {
 	return s.cursor
 }
 
-func (s State[T]) Read(dst []T) (n uint64, next State[T], err error) {
+func (s State[In]) Read(dst []In) (n uint64, next State[In], err error) {
 	n, c, err := s.cursor.Read(dst)
-	return n, State[T]{cursor: c}, err
+	return n, State[In]{cursor: c}, err
 }
 
-func (s State[T]) Pos() uint64 {
+func (s State[In]) Pos() uint64 {
 	return s.cursor.Pos()
 }
 
-func Parse[In, Out any](p Parser[In, Out], c cursor.Cursor[In]) (result Out, err error) {
-	st := State[In]{cursor: c}
-	var reply Result[In, Out]
-	_, reply, err = p(st)
-	return reply.Value, err
-}
-
 type Parser[In, Out any] func(State[In]) (consumed bool, reply Result[In, Out], err error)
 
 func Return[In, Out any](value Out) Parser[In, Out] {
diff --git a/parser_test.go b/parser_test.go
index 74c6409..babbe67 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -27,26 +27,35 @@ func TestSlice(t *testing.T) {
 		s := rapid.SliceOfN(rapid.Byte(), 1, -1).Draw(t, "s")
 		input := rapid.SliceOfN(rapid.Byte(), len(s), -1).
 			Filter(notP(hasPrefix(s))).Draw(t, "input")
-		out, err := gigaparsec.Parse(gigaparsec.Slice(s), cursor.NewSlice(input))
+		start := gigaparsec.MakeState(cursor.NewSlice(input))
+
+		consumed, result, err := gigaparsec.Slice(s)(start)
 		test.ErrorAs(t, err, &gigaparsec.ParseError{})
-		test.SliceEmpty(t, out)
+		test.False(t, consumed, test.Sprint("expected consumed to be false"))
+		test.SliceEmpty(t, result.Value)
 	}))
 	t.Run("fails at end of input", rapid.MakeCheck(func(t *rapid.T) {
 		s := rapid.SliceOfN(rapid.Byte(), 1, -1).Draw(t, "s")
 		inputLen := rapid.IntRange(0, len(s)-1).Draw(t, "inputLen")
 		input := s[:inputLen]
-		out, err := gigaparsec.Parse(gigaparsec.Slice(s), cursor.NewSlice(input))
+		start := gigaparsec.MakeState(cursor.NewSlice(input))
+
+		consumed, result, err := gigaparsec.Slice(s)(start)
 		test.ErrorAs(t, err, &gigaparsec.ParseError{})
-		test.SliceEmpty(t, out)
+		test.False(t, consumed, test.Sprint("expected consumed to be false"))
+		test.SliceEmpty(t, result.Value)
 	}))
 	t.Run("fails when read fails", Todo)
 	t.Run("succeeds when contents match", rapid.MakeCheck(func(t *rapid.T) {
 		input := rapid.SliceOfN(rapid.Byte(), 1, -1).Draw(t, "input")
 		sLen := rapid.IntRange(0, len(input)).Draw(t, "sLen")
 		s := input[:sLen]
-		out, err := gigaparsec.Parse(gigaparsec.Slice(s), cursor.NewSlice(input))
+		start := gigaparsec.MakeState(cursor.NewSlice(input))
+
+		consumed, result, err := gigaparsec.Slice(s)(start)
 		test.NoError(t, err)
-		test.SliceEqOp(t, s, out)
+		test.True(t, consumed, test.Sprint("expected consumed to be true"))
+		test.SliceEqOp(t, s, result.Value)
+		test.EqOp(t, uint64(len(s)), result.State.Pos())
 	}))
-	t.Run("next state has correct position", Todo)
 }