Separate parsing status from actual errors

bytes/regexp.go

@@ -46,18 +46,18 @@ func Regexp(str string) gigaparsec.Parser[byte, []byte] {
 	}
 	re := regexp.MustCompile(str)
 	expected := fmt.Sprintf("match `%s`", str)
-	return func(input gigaparsec.State[byte]) (consumed bool, result gigaparsec.Result[byte, []byte], err error) {
+	return func(input gigaparsec.State[byte]) (gigaparsec.Result[byte, []byte], error) {
 		r := NewRuneReader(input.Cursor())
 		idx := re.FindReaderIndex(r)
 		// TODO Check error from r; this requires an Error() method on cursor.RuneReader.
 		if idx == nil {
-			return false, gigaparsec.Result[byte, []byte]{}, gigaparsec.ParseError{
+			return gigaparsec.Fail[byte, []byte](false, gigaparsec.Message{
 				Pos:      input.Pos(),
 				Expected: []string{expected},
 				// TODO Not having a Got is unsatisfactory, but how do I extract useful information?
 				// Maybe just read a fixed number of bytes or to the end, whichever comes first?
 				// I could add extra methods to cursor.RuneReader to figure out how much it had read.
-			}
+			}), nil
 		}
 		// Alas, this is a little wasteful because a Regexp can only return indices
 		// when searching a RuneReader.
@@ -65,13 +65,9 @@ func Regexp(str string) gigaparsec.Parser[byte, []byte] {
 		n, _, err := input.Cursor().Read(dst)
 		if err != nil {
 			// If we can't access those same bytes again, something is wrong.
-			return false, gigaparsec.Result[byte, []byte]{}, fmt.Errorf("Regex: unexpected error: %w", err)
+			return gigaparsec.Result[byte, []byte]{}, fmt.Errorf("Regex: unexpected error: %w", err)
 		}
-		result = gigaparsec.Result[byte, []byte]{
+		next := input.At(input.Pos() + n)
-			State:   input.At(input.Pos() + n),
+		return gigaparsec.Succeed(true, dst, next, gigaparsec.MessageOK(input.Pos())), nil
-			Value:   dst,
-			Message: gigaparsec.MessageOK(input.Pos()),
-		}
-		return true, result, nil
 	}
 }

gigaparsec.go

@@ -10,9 +10,57 @@ import (
 )
 
 type Result[In, Out any] struct {
-	Value Out
+	consumed, failed bool
-	State[In]
+	Value            Out
-	Message
+	next             State[In]
+	Message          Message
+}
+
+func Fail[In, Out any](consumed bool, msg Message) Result[In, Out] {
+	return Result[In, Out]{
+		consumed: consumed,
+		failed:   true,
+		Message:  msg,
+	}
+}
+
+func (r Result[In, Out]) Failed() (ok, consumed bool, msg Message) {
+	ok = r.failed
+	if ok {
+		consumed = r.consumed
+		msg = r.Message
+	}
+	return
+}
+
+func Succeed[In, Out any](consumed bool, value Out, next State[In], msg Message) Result[In, Out] {
+	return Result[In, Out]{
+		failed:   false,
+		Value:    value,
+		consumed: consumed,
+		next:     next,
+		Message:  msg,
+	}
+}
+
+func (r Result[In, Out]) Succeeded() (ok, consumed bool, value Out, next State[In], msg Message) {
+	ok = !r.failed
+	if ok {
+		consumed = r.consumed
+		value = r.Value
+		next = r.next
+		msg = r.Message
+	}
+	return
+}
+
+func (r Result[In, Out]) Consumed() bool {
+	return r.consumed
+}
+
+func (r Result[In, Out]) Consume(consumed bool) Result[In, Out] {
+	r.consumed = consumed
+	return r
 }
 
 type Message struct {
@@ -30,11 +78,11 @@ func MessageOK(pos uint64) Message { return Message{Pos: pos} }
 
 func MessageEnd(pos uint64) Message { return Message{Pos: pos, Got: "end of input"} }
 
-type ParseError Message
+// type ParseError Message
 
-func (pe ParseError) Error() string {
+// func (pe ParseError) Error() string {
-	return fmt.Sprintf("parse error: %d: %s", pe.Pos, pe.Got)
+// 	return fmt.Sprintf("parse error: %d: %s", pe.Pos, pe.Got)
-}
+// }
 
 func MakeState[In any](c cursor.Cursor[In]) State[In] {
 	return State[In]{cursor: c}
@@ -61,125 +109,115 @@ func (s State[In]) At(pos uint64) State[In] {
 	return State[In]{cursor: s.cursor.At(pos)}
 }
 
-type Parser[In, Out any] func(State[In]) (consumed bool, reply Result[In, Out], err error)
+type Parser[In, Out any] func(State[In]) (Result[In, Out], error)
 
 func Return[In, Out any](value Out) Parser[In, Out] {
-	return func(state State[In]) (bool, Result[In, Out], error) {
+	return func(state State[In]) (Result[In, Out], error) {
-		return false, Result[In, Out]{
+		return Succeed(false, value, state, MessageOK(state.Pos())), nil
-			Value:   value,
-			State:   state,
-			Message: MessageOK(state.Pos()),
-		}, nil
 	}
 }
 
 func Satisfy[T any](pred func(T) bool) Parser[T, T] {
-	return func(state State[T]) (bool, Result[T, T], error) {
+	return func(state State[T]) (Result[T, T], error) {
 		token := make([]T, 1)
 		n, next, err := state.Read(token)
 		if errors.Is(err, io.EOF) {
-			return false, Result[T, T]{}, ParseError(MessageEnd(state.Pos()))
+			return Fail[T, T](false, MessageEnd(state.Pos())), nil
 		}
 		if err != nil {
-			return false, Result[T, T]{}, err
+			return Result[T, T]{}, err
 		}
 		if n != 1 {
 			panic(fmt.Sprintf("expected 1 element from Read, but got %d", n))
 		}
 		if pred(token[0]) {
-			return true, Result[T, T]{
+			return Succeed(true, token[0], next, MessageOK(state.Pos())), nil
-				Value:   token[0],
-				State:   next,
-				Message: MessageOK(state.Pos()),
-			}, nil
 		}
-		return false, Result[T, T]{}, ParseError{
+		return Fail[T, T](false, Message{
 			Pos: state.Pos(),
 			Got: fmt.Sprint(token),
-		}
+		}), nil
 	}
 }
 
 func Slice[T comparable](s []T) Parser[T, []T] {
 	expected := fmt.Sprint(s)
-	return func(state State[T]) (consumed bool, reply Result[T, []T], err error) {
+	return func(state State[T]) (reply Result[T, []T], err error) {
 		token := make([]T, len(s))
 		_, next, err := state.Read(token)
 		if errors.Is(err, io.EOF) {
-			return false, Result[T, []T]{}, ParseError(MessageEnd(state.Pos()))
+			return Fail[T, []T](false, MessageEnd(state.Pos())), nil
 		}
 		if err != nil {
-			return false, Result[T, []T]{}, err
+			return Result[T, []T]{}, err
 		}
 		if !slices.Equal(s, token) {
-			return false, Result[T, []T]{}, ParseError{
+			return Fail[T, []T](false, Message{
 				Pos:      state.Pos(),
 				Got:      fmt.Sprint(token),
 				Expected: []string{expected},
-			}
+			}), nil
 		}
-		return true, Result[T, []T]{
+		return Succeed(true, token, next, MessageOK(state.Pos())), nil
-			Value:   token,
-			State:   next,
-			Message: MessageOK(state.Pos()),
-		}, nil
 	}
 }
 
 func Bind[In, A, B any](p Parser[In, A], f func(A) Parser[In, B]) Parser[In, B] {
-	return func(input State[In]) (bool, Result[In, B], error) {
+	return func(input State[In]) (Result[In, B], error) {
-		consumed, resultA, err := p(input)
+		resultA, err := p(input)
 		if err != nil {
-			return false, Result[In, B]{}, err
+			return Result[In, B]{}, err
 		}
-		consumed2, replyB, err := f(resultA.Value)(resultA.State)
+		if ok, consumed, msg := resultA.Failed(); ok {
-		return consumed || consumed2, replyB, err
+			return Fail[In, B](consumed, msg), nil
+		}
+
+		_, consumedA, valueA, next, _ := resultA.Succeeded()
+		resultB, err := f(valueA)(next)
+		if err != nil {
+			return Result[In, B]{}, err
+		}
+		return resultB.Consume(consumedA || resultB.Consumed()), nil
 	}
 }
 
 func Choose[In, Out any](p Parser[In, Out], ps ...Parser[In, Out]) Parser[In, Out] {
+	// TODO Check this against the Parsec paper again, and simplify it.
 	all := append([]Parser[In, Out]{p}, ps...)
-	return func(input State[In]) (bool, Result[In, Out], error) {
+	return func(input State[In]) (Result[In, Out], error) {
 		expecteds := make([][]string, 0, len(all))
 		var value Out
 		var got string
-		var gotGot bool
 		var failed bool
 		for _, q := range all {
-			consumed, result, err := q(input)
+			result, err := q(input)
-			if consumed {
+			if err != nil {
-				return consumed, result, err
+				return Result[In, Out]{}, err
+			}
+			if result.Consumed() {
+				return result, nil
 			}
 			var qMsg Message
-			if err != nil {
+			if isFailure, _, msg := result.Failed(); isFailure {
-				var parseErr ParseError
+				qMsg = msg
-				if !errors.As(err, &parseErr) {
+				failed = true
-					// It broke. Give up.
-					return consumed, result, err
-				}
-				failed = failed && true
-				qMsg = Message(parseErr)
 			} else {
+				_, _, qValue, _, msg := result.Succeeded()
 				if failed {
-					value = result.Value
+					value = qValue
 					failed = false
 				}
-				qMsg = result.Message
+				qMsg = msg
 			}
-			if !gotGot {
+			if got == "" {
 				got = qMsg.Got
-				gotGot = true
 			}
 		}
 		msg := Message{Pos: input.Pos(), Got: got, Expected: slices.Concat(expecteds...)}
 		if failed {
-			return false, Result[In, Out]{}, ParseError(msg)
+			return Fail[In, Out](false, msg), nil
 		}
-		return false, Result[In, Out]{
+		return Succeed(false, value, input, msg), nil
-			Value:   value,
-			State:   input,
-			Message: msg,
-		}, nil
 	}
 }
 
@@ -189,31 +227,29 @@ func Choose[In, Out any](p Parser[In, Out], ps ...Parser[In, Out]) Parser[In, Ou
 // parser consumed nothing, Try will allow backing out of a complex
 // parser that did partially succeeded.
 func Try[In, Out any](p Parser[In, Out]) Parser[In, Out] {
-	return func(input State[In]) (bool, Result[In, Out], error) {
+	return func(input State[In]) (Result[In, Out], error) {
-		consumed, reply, err := p(input)
+		result, err := p(input)
 		if err != nil {
-			return false, Result[In, Out]{}, err
+			return result, err
 		}
-		return consumed, reply, err
+		if failed, _, msg := result.Failed(); failed {
+			return Fail[In, Out](false, msg), nil
+		}
+		return result, nil
 	}
 }
 
 func Label[In, Out any](p Parser[In, Out], l string) Parser[In, Out] {
-	return func(input State[In]) (consumed bool, reply Result[In, Out], err error) {
+	return func(input State[In]) (reply Result[In, Out], err error) {
-		consumed, reply, err = p(input)
+		result, err := p(input)
-		if consumed {
+		if err != nil || result.Consumed() {
-			return
+			return result, err
 		}
-		if err == nil {
+		if succeeded, _, value, next, msg := result.Succeeded(); succeeded {
-			reply.Message = reply.Message.expect(l)
+			return Succeed(false, value, next, msg.expect(l)), nil
-			return
 		}
-		var parseErr ParseError
+		_, _, msg := result.Failed()
-		if errors.As(err, &parseErr) {
+		return Fail[In, Out](false, msg.expect(l)), nil
-			err = ParseError(Message(parseErr).expect(l))
-			return
-		}
-		return
 	}
 }
 
@@ -223,21 +259,17 @@ func Map[In, Out1, Out2 any](p Parser[In, Out1], f func(Out1) Out2) Parser[In, O
 	})
 }
 
-func End[In any](s State[In]) (consumed bool, reply Result[In, struct{}], err error) {
+func End[In any](s State[In]) (reply Result[In, struct{}], err error) {
 	_, _, err = s.cursor.Read([]In{})
 	if errors.Is(err, io.EOF) {
-		reply := Result[In, struct{}]{
+		return Succeed(true, struct{}{}, s, MessageOK(s.Pos())), nil
-			State:   s,
-			Message: MessageOK(s.Pos()),
-		}
-		return true, reply, nil
 	}
 	if err != nil {
-		return false, Result[In, struct{}]{}, fmt.Errorf("End: unexpected error: %w", err)
+		return Result[In, struct{}]{}, fmt.Errorf("End: unexpected error: %w", err)
 	}
-	return false, Result[In, struct{}]{}, ParseError{
+	return Fail[In, struct{}](false, Message{
 		Pos:      s.Pos(),
 		Got:      "",
 		Expected: []string{"end of input"},
-	}
+	}), nil
 }

parser_test.go

@@ -7,6 +7,7 @@ import (
 	"git.codemonkeysoftware.net/b/gigaparsec"
 	"git.codemonkeysoftware.net/b/gigaparsec/cursor"
 	"github.com/shoenig/test"
+	"github.com/shoenig/test/must"
 	"pgregory.net/rapid"
 )
 
@@ -23,17 +24,17 @@ func hasPrefix(prefix []byte) func([]byte) bool {
 }
 
 func TestSlice(t *testing.T) {
-	assertParseFails := func(t rapid.TB, input []byte, p gigaparsec.Parser[byte, []byte]) (parseErr gigaparsec.ParseError) {
+	assertParseFails := func(t rapid.TB, input []byte, p gigaparsec.Parser[byte, []byte]) {
 		t.Helper()
 		start := gigaparsec.MakeState(cursor.NewSlice(input))
-		consumed, result, err := p(start)
+		result, err := p(start)
-		test.ErrorAs(t, err, &parseErr, test.Sprint("expected ParseError"))
+		must.NoError(t, err)
-		test.False(t, consumed, test.Sprint("expected consumed to be false"))
+		failed, consumed, _ := result.Failed()
-		test.SliceEmpty(t, result.Value, test.Sprint("expected result value to be empty"))
+		test.True(t, failed)
+		test.False(t, consumed)
 		if t.Failed() {
 			t.FailNow()
 		}
-		return parseErr
 	}
 
 	t.Run("fails with wrong contents", rapid.MakeCheck(func(t *rapid.T) {
@@ -55,11 +56,13 @@ func TestSlice(t *testing.T) {
 		s := input[:sLen]
 		start := gigaparsec.MakeState(cursor.NewSlice(input))
 
-		consumed, result, err := gigaparsec.Slice(s)(start)
+		result, err := gigaparsec.Slice(s)(start)
-		test.NoError(t, err)
+		must.NoError(t, err)
-		test.True(t, consumed, test.Sprint("expected consumed to be true"))
+		succeeded, consumed, value, next, _ := result.Succeeded()
-		test.SliceEqOp(t, s, result.Value)
+		test.True(t, succeeded)
-		test.EqOp(t, uint64(len(s)), result.State.Pos())
+		test.True(t, consumed)
+		test.SliceEqOp(t, s, value)
+		test.EqOp(t, uint64(len(s)), next.Pos())
 	}))
 }