Added Bracket, Where, and Token (without tests)

README.md

@@ -1,8 +1,8 @@
 # Gigaparsec
 
 [![Go Reference](https://pkg.go.dev/badge/git.codemonkeysoftware.net/b/gigaparsec.svg)](https://pkg.go.dev/git.codemonkeysoftware.net/b/gigaparsec)
-![Total garbage.](https://img.shields.io/badge/Total-garbage-red)
+
+by Brandon Dyck <[brandon@dyck.us](mailto:brandon@dyck.us)>
 
 Monadic parser combinators in Go
 
-**I don't recommend using this yet. It is very unfinished and it will break.**

TODO.txt

@@ -1,6 +1,9 @@
-Write Repeat tests
 Think about not requiring so much Pos() when making messages
+Think about changing "consume" to "commit"
 Rename Seq2 to Seq
 Document Seq
 Should MakeState be private now that there's Run?
 What's Megaparsec got that we ain't got?
+Add and benchmark naïve Seq
+chainl
+whitespace handling

bind.go

@@ -278,3 +278,421 @@ func Bind5[In, Out, T, T2, T3, T4, T5 any](
 		return Succeed(anyConsumed, val6, next, MessageOK(s.Pos())), nil
 	}
 }
+
+// Bind6 is equivalent to 6 nested calls to Bind.
+func Bind6[In, Out, T, T2, T3, T4, T5, T6 any](
+	p Parser[In, T],
+	f func(T) Parser[In, T2],
+	f2 func(T2) Parser[In, T3],
+	f3 func(T3) Parser[In, T4],
+	f4 func(T4) Parser[In, T5],
+	f5 func(T5) Parser[In, T6],
+	f6 func(T6) Parser[In, Out],
+) Parser[In, Out] {
+	return func(s State[In]) (Result[In, Out], error) {
+		var anyConsumed bool
+		var next = s
+
+		r, err := p(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r.Consumed()
+		success, val, next := r.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r.Message()), nil
+		}
+
+		r2, err := f(val)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r2.Consumed()
+		success, val2, next := r2.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r2.Message()), nil
+		}
+
+		r3, err := f2(val2)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r3.Consumed()
+		success, val3, next := r3.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r3.Message()), nil
+		}
+
+		r4, err := f3(val3)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r4.Consumed()
+		success, val4, next := r4.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r4.Message()), nil
+		}
+
+		r5, err := f4(val4)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r5.Consumed()
+		success, val5, next := r5.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r5.Message()), nil
+		}
+
+		r6, err := f5(val5)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r6.Consumed()
+		success, val6, next := r6.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r6.Message()), nil
+		}
+
+		r7, err := f6(val6)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r7.Consumed()
+		success, val7, next := r7.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r7.Message()), nil
+		}
+
+		return Succeed(anyConsumed, val7, next, MessageOK(s.Pos())), nil
+	}
+}
+
+// Bind7 is equivalent to 7 nested calls to Bind.
+func Bind7[In, Out, T, T2, T3, T4, T5, T6, T7 any](
+	p Parser[In, T],
+	f func(T) Parser[In, T2],
+	f2 func(T2) Parser[In, T3],
+	f3 func(T3) Parser[In, T4],
+	f4 func(T4) Parser[In, T5],
+	f5 func(T5) Parser[In, T6],
+	f6 func(T6) Parser[In, T7],
+	f7 func(T7) Parser[In, Out],
+) Parser[In, Out] {
+	return func(s State[In]) (Result[In, Out], error) {
+		var anyConsumed bool
+		var next = s
+
+		r, err := p(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r.Consumed()
+		success, val, next := r.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r.Message()), nil
+		}
+
+		r2, err := f(val)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r2.Consumed()
+		success, val2, next := r2.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r2.Message()), nil
+		}
+
+		r3, err := f2(val2)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r3.Consumed()
+		success, val3, next := r3.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r3.Message()), nil
+		}
+
+		r4, err := f3(val3)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r4.Consumed()
+		success, val4, next := r4.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r4.Message()), nil
+		}
+
+		r5, err := f4(val4)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r5.Consumed()
+		success, val5, next := r5.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r5.Message()), nil
+		}
+
+		r6, err := f5(val5)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r6.Consumed()
+		success, val6, next := r6.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r6.Message()), nil
+		}
+
+		r7, err := f6(val6)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r7.Consumed()
+		success, val7, next := r7.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r7.Message()), nil
+		}
+
+		r8, err := f7(val7)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r8.Consumed()
+		success, val8, next := r8.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r8.Message()), nil
+		}
+
+		return Succeed(anyConsumed, val8, next, MessageOK(s.Pos())), nil
+	}
+}
+
+// Bind8 is equivalent to 8 nested calls to Bind.
+func Bind8[In, Out, T, T2, T3, T4, T5, T6, T7, T8 any](
+	p Parser[In, T],
+	f func(T) Parser[In, T2],
+	f2 func(T2) Parser[In, T3],
+	f3 func(T3) Parser[In, T4],
+	f4 func(T4) Parser[In, T5],
+	f5 func(T5) Parser[In, T6],
+	f6 func(T6) Parser[In, T7],
+	f7 func(T7) Parser[In, T8],
+	f8 func(T8) Parser[In, Out],
+) Parser[In, Out] {
+	return func(s State[In]) (Result[In, Out], error) {
+		var anyConsumed bool
+		var next = s
+
+		r, err := p(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r.Consumed()
+		success, val, next := r.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r.Message()), nil
+		}
+
+		r2, err := f(val)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r2.Consumed()
+		success, val2, next := r2.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r2.Message()), nil
+		}
+
+		r3, err := f2(val2)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r3.Consumed()
+		success, val3, next := r3.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r3.Message()), nil
+		}
+
+		r4, err := f3(val3)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r4.Consumed()
+		success, val4, next := r4.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r4.Message()), nil
+		}
+
+		r5, err := f4(val4)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r5.Consumed()
+		success, val5, next := r5.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r5.Message()), nil
+		}
+
+		r6, err := f5(val5)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r6.Consumed()
+		success, val6, next := r6.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r6.Message()), nil
+		}
+
+		r7, err := f6(val6)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r7.Consumed()
+		success, val7, next := r7.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r7.Message()), nil
+		}
+
+		r8, err := f7(val7)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r8.Consumed()
+		success, val8, next := r8.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r8.Message()), nil
+		}
+
+		r9, err := f8(val8)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r9.Consumed()
+		success, val9, next := r9.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r9.Message()), nil
+		}
+
+		return Succeed(anyConsumed, val9, next, MessageOK(s.Pos())), nil
+	}
+}
+
+// Bind9 is equivalent to 9 nested calls to Bind.
+func Bind9[In, Out, T, T2, T3, T4, T5, T6, T7, T8, T9 any](
+	p Parser[In, T],
+	f func(T) Parser[In, T2],
+	f2 func(T2) Parser[In, T3],
+	f3 func(T3) Parser[In, T4],
+	f4 func(T4) Parser[In, T5],
+	f5 func(T5) Parser[In, T6],
+	f6 func(T6) Parser[In, T7],
+	f7 func(T7) Parser[In, T8],
+	f8 func(T8) Parser[In, T9],
+	f9 func(T9) Parser[In, Out],
+) Parser[In, Out] {
+	return func(s State[In]) (Result[In, Out], error) {
+		var anyConsumed bool
+		var next = s
+
+		r, err := p(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r.Consumed()
+		success, val, next := r.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r.Message()), nil
+		}
+
+		r2, err := f(val)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r2.Consumed()
+		success, val2, next := r2.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r2.Message()), nil
+		}
+
+		r3, err := f2(val2)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r3.Consumed()
+		success, val3, next := r3.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r3.Message()), nil
+		}
+
+		r4, err := f3(val3)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r4.Consumed()
+		success, val4, next := r4.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r4.Message()), nil
+		}
+
+		r5, err := f4(val4)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r5.Consumed()
+		success, val5, next := r5.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r5.Message()), nil
+		}
+
+		r6, err := f5(val5)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r6.Consumed()
+		success, val6, next := r6.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r6.Message()), nil
+		}
+
+		r7, err := f6(val6)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r7.Consumed()
+		success, val7, next := r7.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r7.Message()), nil
+		}
+
+		r8, err := f7(val7)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r8.Consumed()
+		success, val8, next := r8.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r8.Message()), nil
+		}
+
+		r9, err := f8(val8)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r9.Consumed()
+		success, val9, next := r9.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r9.Message()), nil
+		}
+
+		r10, err := f9(val9)(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r10.Consumed()
+		success, val10, next := r10.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r10.Message()), nil
+		}
+
+		return Succeed(anyConsumed, val10, next, MessageOK(s.Pos())), nil
+	}
+}

bytes/bytes.go

@@ -0,0 +1,16 @@
+package bytes
+
+import (
+	"git.codemonkeysoftware.net/b/gigaparsec"
+)
+
+func Token[Out, WSOut any](whitespace gigaparsec.Parser[byte, WSOut]) func(p gigaparsec.Parser[byte, Out]) gigaparsec.Parser[byte, Out] {
+	mappedWS := gigaparsec.Map(whitespace, func(WSOut) struct{} { return struct{}{} })
+	var ignoreWS gigaparsec.Parser[byte, struct{}] = func(s gigaparsec.State[byte]) (gigaparsec.Result[byte, struct{}], error) {
+		result, err := mappedWS(s)
+		return result.Consume(false), err
+	}
+	return func(p gigaparsec.Parser[byte, Out]) gigaparsec.Parser[byte, Out] {
+		return gigaparsec.Seq2(p, gigaparsec.Repeat(0, ignoreWS), func(val Out, _ []struct{}) Out { return val })
+	}
+}

bytes/regexp.go

@@ -69,6 +69,9 @@ func Regexp(pattern string) gigaparsec.Parser[byte, string] {
 			return gigaparsec.Result[byte, string]{}, fmt.Errorf("Regexp: reader error: %w", err)
 		}
 		if idx == nil {
+			if err == io.EOF {
+				return gigaparsec.Fail[byte, string](false, gigaparsec.MessageEnd(input.Pos())), nil
+			}
 			got := make([]byte, r.Count())
 			_, _, err = input.Read(got)
 			if err != nil {
@@ -80,7 +83,7 @@ func Regexp(pattern string) gigaparsec.Parser[byte, string] {
 		// when searching a RuneReader.
 		dst := make([]byte, idx[1]-idx[0])
 		n, _, err := input.Read(dst)
-		if err != nil {
+		if err != nil && (!errors.Is(err, io.EOF) || n < uint64(len(dst))) {
 			return gigaparsec.Result[byte, string]{}, fmt.Errorf("Regexp: unexpected error: %w", err)
 		}
 		next := input.At(input.Pos() + n)

bytes/regexp_test.go

@@ -4,6 +4,7 @@ package bytes_test
 
 import (
 	"bytes"
+	"errors"
 	"strings"
 	"testing"
 
@@ -16,24 +17,64 @@ import (
 	"pgregory.net/rapid"
 )
 
-func Todo(t *testing.T) {
-	t.Fatalf("TODO")
-}
-
 func TestRegexp(t *testing.T) {
-	t.Run("only searches the beginning of input", Todo)
-	t.Run("position is correct after match", Todo)
-	t.Run("fails on unexpected error", Todo)
-	t.Run("returns a useful Got value", rapid.MakeCheck(func(t *rapid.T) {
+	alpha := rapid.SliceOfBytesMatching(`[A-Za-z]{1,100}`)
+	t.Run("position and value are correct after match", rapid.MakeCheck(func(t *rapid.T) {
+		needle := alpha.Draw(t, "needle")
+		input := rapid.Map(alpha, func(suffix []byte) []byte { return append(needle, suffix...) }).
+			Draw(t, "input")
+
+		p := pbytes.Regexp(string(needle))
+		result, err := p(gigaparsec.MakeState(bytes.NewReader(input)))
+		succeeded, val, next := result.Status()
 
-	}))
-	t.Run("basically works", func(t *testing.T) {
-		result, err := pbytes.Regexp("a")(gigaparsec.MakeState(strings.NewReader("a")))
 		must.NoError(t, err)
-		success, value, _ := result.Status()
-		test.True(t, success, test.Sprint(result.Message()))
-		test.EqOp(t, "a", value)
-		test.True(t, result.Consumed())
+		test.True(t, succeeded)
+		test.EqOp(t, string(needle), val)
+		ptest.StateIsAt(t, next, uint64(len(needle)))
+	}))
+	t.Run("only searches the beginning of input", rapid.MakeCheck(func(t *rapid.T) {
+		needle := alpha.Draw(t, "needle")
+		input := rapid.Map(alpha, func(prefix []byte) []byte { return append(prefix, needle...) }).
+			Filter(func(b []byte) bool { return !bytes.HasPrefix(b, needle) }).
+			Draw(t, "input")
+
+		p := pbytes.Regexp(string(needle))
+		result, err := p(gigaparsec.MakeState(bytes.NewReader(input)))
+		succeeded, _, _ := result.Status()
+
+		must.NoError(t, err)
+		test.False(t, succeeded)
+	}))
+	t.Run("fails on unexpected error", func(t *testing.T) {
+		expectedErr := errors.New("it broke")
+		p := pbytes.Regexp("nope")
+		result, err := p(gigaparsec.MakeState(ptest.ErrReaderAt(expectedErr)))
+		succeeded, _, _ := result.Status()
+		test.ErrorIs(t, err, expectedErr)
+		test.False(t, succeeded)
+	})
+	t.Run("returns a useful Got value", func(t *testing.T) {
+		p := pbytes.Regexp("hello")
+		result, err := p(gigaparsec.MakeState(strings.NewReader("hellaparsec")))
+
+		must.NoError(t, err)
+		test.StrContains(t, result.Message().Got(), "hella")
+	})
+	t.Run("succeeds on empty matches", func(t *testing.T) {
+		p := pbytes.Regexp(".*")
+		result, err := p(gigaparsec.MakeState(strings.NewReader("")))
+		succeeded, value, _ := result.Status()
+		must.NoError(t, err)
+		must.True(t, succeeded)
+		must.EqOp(t, "", value)
+	})
+	t.Run("fails without an error at EOF", func(t *testing.T) {
+		p := pbytes.Regexp("a")
+		result, err := p(gigaparsec.MakeState(strings.NewReader("")))
+		succeeded, _, _ := result.Status()
+		must.NoError(t, err)
+		must.False(t, succeeded)
 	})
 }
 

gigaparsec.go

@@ -2,11 +2,12 @@
 
 package gigaparsec
 
-//go:generate go run ./internal/bindgen -bindpath bind.go -seqpath seq.go -max 5 -pkg gigaparsec
+//go:generate go run ./internal/bindgen -bindpath bind.go -seqpath seq.go -max 9 -pkg gigaparsec
 import (
 	"errors"
 	"fmt"
 	"io"
+	"math"
 	"slices"
 	"strings"
 )
@@ -116,6 +117,22 @@ type ReaderAt[T any] interface {
 	ReadAt(p []T, off int64) (n int, err error)
 }
 
+type SliceReaderAt[T any] []T
+
+func (s SliceReaderAt[T]) ReadAt(dst []T, off int64) (n int, err error) {
+	if off < 0 {
+		return 0, errors.New("SliceReaderAt.ReadAt: negative offset")
+	}
+	if off >= int64(len(s)) {
+		return 0, io.EOF
+	}
+	n = copy(dst, s[off:])
+	if n < len(dst) {
+		err = io.EOF
+	}
+	return n, err
+}
+
 func MakeState[In any](r ReaderAt[In]) State[In] {
 	return State[In]{r: r}
 }
@@ -125,18 +142,36 @@ type State[In any] struct {
 	pos uint64
 }
 
+// Read fills dst with data from this State's position in the underlying source.
+// It returns the number of data it read and a new State for the position at which
+// the read ended, and an error if the read either (1) failed or (2) reached the
+// end of the source before filling dst. All reads from a given State will return
+// data from the same position the source.
+// If the source had too few data left to fill dst, or if the State's position is
+// at or past the end of the source, err will be io.EOF.
 func (s State[In]) Read(dst []In) (n uint64, next State[In], err error) {
+	if s.pos > math.MaxInt64 {
+		return 0, s, io.EOF
+	}
 	nread, err := s.r.ReadAt(dst, int64(s.pos))
 	if nread > 0 {
 		s.pos += uint64(nread)
 	}
+	if nread == len(dst) && err == io.EOF {
+		if nread == 0 {
+			return 0, s, io.EOF
+		}
+		return uint64(nread), s, nil
+	}
 	return uint64(nread), s, err
 }
 
+// Pos returns this State's position.
 func (s State[In]) Pos() uint64 {
 	return s.pos
 }
 
+// At returns a State pointing at pos in the same data source.
 func (s State[In]) At(pos uint64) State[In] {
 	return State[In]{r: s.r, pos: pos}
 }
@@ -159,6 +194,17 @@ func (p Parser[In, Out]) Label(label string) Parser[In, Out] {
 	}
 }
 
+func (p Parser[In, Out]) Where(pred func(Out) bool) Parser[In, Out] {
+	return func(s State[In]) (Result[In, Out], error) {
+		result, err := p(s)
+		if result.success && !pred(result.value) {
+			result.success = false
+			result.message.got = "failed Where predicate"
+		}
+		return result, err
+	}
+}
+
 type ParseError Message
 
 func (pe ParseError) Error() string {
@@ -344,26 +390,40 @@ func Pipe[In, Ignore, Through any](p Parser[In, Ignore]) func(Through) Parser[In
 // It succeeds if and only if p succeeds at least minCount times.
 // It consumes if and only if at least one of the applications of p consumes.
 func Repeat[In, Out any](minCount int, p Parser[In, Out]) Parser[In, []Out] {
-	return func(s State[In]) (Result[In, []Out], error) {
+	return func(state State[In]) (Result[In, []Out], error) {
 		var values []Out
 		var consumed bool
-		next := s
+		currState := state
 		for {
-			result, err := p(next)
+			result, err := p(currState)
 			if err != nil {
 				return Result[In, []Out]{}, fmt.Errorf("AtLeastN: %w", err)
 			}
 			consumed = consumed || result.Consumed()
 			var value Out
 			var success bool
-			success, value, next = result.Status()
+			success, value, nextState := result.Status()
 			if !success {
 				if len(values) >= minCount {
-					return Succeed(consumed, values, next, MessageOK(s.Pos())), nil
+					return Succeed(consumed, values, currState, MessageOK(state.Pos())), nil
 				}
 				return Fail[In, []Out](consumed, result.Message()), nil
 			}
+			currState = nextState
 			values = append(values, value)
 		}
 	}
 }
+
+// Lazy delays creating a parser from p until the parser is called.
+// This is useful for preventing recursive function calls in the
+// definition of a recursive parser.
+func Lazy[In, Out any](p func() Parser[In, Out]) Parser[In, Out] {
+	return func(s State[In]) (Result[In, Out], error) {
+		return p()(s)
+	}
+}
+
+func Bracket[In, Out, LOut, ROut any](left Parser[In, LOut], p Parser[In, Out], right Parser[In, ROut]) Parser[In, Out] {
+	return Seq3(left, p, right, func(_ LOut, val Out, _ ROut) Out { return val })
+}

internal/check/check.go

@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: Unlicense
+
+package main
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+)
+
+var goSpdxHeader = `// SPDX-License-Identifier: Unlicense`
+var tmplSpdxHeader = `{{/* SPDX-License-Identifier: Unlicense */`
+
+type MissingSPDXError struct {
+	Name string
+}
+
+func (m MissingSPDXError) Error() string {
+	return fmt.Sprintf("missing or incorrect SPDX header: %s", m.Name)
+}
+
+func checkFileSPDX(header string, name string) error {
+	f, err := os.Open(name)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	r := bufio.NewReader(f)
+	pattern := `(?m:^` + regexp.QuoteMeta(header) + `)`
+	matched, err := regexp.MatchReader(pattern, r)
+	if err != nil {
+		return err
+	}
+	if !matched {
+		return MissingSPDXError{Name: name}
+	}
+	return nil
+}
+
+func walkSPDX(header string, extension string) error {
+	var errs []error
+	filepath.WalkDir(".", func(path string, d fs.DirEntry, err error) error {
+		if path != "." && strings.HasPrefix(path, ".") {
+			if d.IsDir() {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+		if err != nil {
+			errs = append(errs, err)
+			return nil
+		}
+
+		if filepath.Ext(path) != extension {
+			return nil
+		}
+		errs = append(errs, checkFileSPDX(header, path))
+		return nil
+	})
+	return errors.Join(errs...)
+}
+
+func checkSPDX() error {
+	err := errors.Join(
+		walkSPDX(goSpdxHeader, ".go"),
+		walkSPDX(tmplSpdxHeader, ".tmpl"),
+	)
+	if err != nil {
+		return fmt.Errorf("Check SPDX Headers:\n%w", err)
+	}
+	return nil
+}
+
+func run() error {
+	return checkSPDX()
+}
+
+func main() {
+	err := run()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}

naive/naive.go

@@ -0,0 +1,265 @@
+// SPDX-License-Identifier: Unlicense
+
+// Package naive contains naïve implementations of the Bind and Seq combinators.
+// The accompanying tests include simple benchmarks comparing their performance.
+package naive
+
+import gp "git.codemonkeysoftware.net/b/gigaparsec"
+
+func Bind2[In, Out, T, T2 any](
+	p gp.Parser[In, T],
+	f func(T) gp.Parser[In, T2],
+	f2 func(T2) gp.Parser[In, Out],
+) gp.Parser[In, Out] {
+	return gp.Bind(gp.Bind(p, f), f2)
+}
+func Bind3[In, Out, T, T2, T3, T4, T5, T6, T7, T8, T9 any](
+	p gp.Parser[In, T],
+	f func(T) gp.Parser[In, T2],
+	f2 func(T2) gp.Parser[In, T3],
+	f3 func(T3) gp.Parser[In, Out],
+) gp.Parser[In, Out] {
+	return gp.Bind(gp.Bind(gp.Bind(p, f), f2), f3)
+}
+func Bind4[In, Out, T, T2, T3, T4 any](
+	p gp.Parser[In, T],
+	f func(T) gp.Parser[In, T2],
+	f2 func(T2) gp.Parser[In, T3],
+	f3 func(T3) gp.Parser[In, T4],
+	f4 func(T4) gp.Parser[In, Out],
+) gp.Parser[In, Out] {
+	return gp.Bind(gp.Bind(gp.Bind(gp.Bind(p, f), f2), f3), f4)
+}
+func Bind5[In, Out, T, T2, T3, T4, T5 any](
+	p gp.Parser[In, T],
+	f func(T) gp.Parser[In, T2],
+	f2 func(T2) gp.Parser[In, T3],
+	f3 func(T3) gp.Parser[In, T4],
+	f4 func(T4) gp.Parser[In, T5],
+	f5 func(T5) gp.Parser[In, Out],
+) gp.Parser[In, Out] {
+	return gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(p, f), f2), f3), f4), f5)
+}
+func Bind6[In, Out, T, T2, T3, T4, T5, T6 any](
+	p gp.Parser[In, T],
+	f func(T) gp.Parser[In, T2],
+	f2 func(T2) gp.Parser[In, T3],
+	f3 func(T3) gp.Parser[In, T4],
+	f4 func(T4) gp.Parser[In, T5],
+	f5 func(T5) gp.Parser[In, T6],
+	f6 func(T6) gp.Parser[In, Out],
+) gp.Parser[In, Out] {
+	return gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(p, f), f2), f3), f4), f5), f6)
+}
+func Bind7[In, Out, T, T2, T3, T4, T5, T6, T7 any](
+	p gp.Parser[In, T],
+	f func(T) gp.Parser[In, T2],
+	f2 func(T2) gp.Parser[In, T3],
+	f3 func(T3) gp.Parser[In, T4],
+	f4 func(T4) gp.Parser[In, T5],
+	f5 func(T5) gp.Parser[In, T6],
+	f6 func(T6) gp.Parser[In, T7],
+	f7 func(T7) gp.Parser[In, Out],
+) gp.Parser[In, Out] {
+	return gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(p, f), f2), f3), f4), f5), f6), f7)
+}
+func Bind8[In, Out, T, T2, T3, T4, T5, T6, T7, T8 any](
+	p gp.Parser[In, T],
+	f func(T) gp.Parser[In, T2],
+	f2 func(T2) gp.Parser[In, T3],
+	f3 func(T3) gp.Parser[In, T4],
+	f4 func(T4) gp.Parser[In, T5],
+	f5 func(T5) gp.Parser[In, T6],
+	f6 func(T6) gp.Parser[In, T7],
+	f7 func(T7) gp.Parser[In, T8],
+	f8 func(T8) gp.Parser[In, Out],
+) gp.Parser[In, Out] {
+	return gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(p, f), f2), f3), f4), f5), f6), f7), f8)
+}
+func Bind9[In, Out, T, T2, T3, T4, T5, T6, T7, T8, T9 any](
+	p gp.Parser[In, T],
+	f func(T) gp.Parser[In, T2],
+	f2 func(T2) gp.Parser[In, T3],
+	f3 func(T3) gp.Parser[In, T4],
+	f4 func(T4) gp.Parser[In, T5],
+	f5 func(T5) gp.Parser[In, T6],
+	f6 func(T6) gp.Parser[In, T7],
+	f7 func(T7) gp.Parser[In, T8],
+	f8 func(T8) gp.Parser[In, T9],
+	f9 func(T9) gp.Parser[In, Out],
+) gp.Parser[In, Out] {
+	return gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(gp.Bind(p, f), f2), f3), f4), f5), f6), f7), f8), f9)
+}
+
+func Seq2[In, Out, T, T2 any](
+	p gp.Parser[In, T],
+	p2 gp.Parser[In, T2],
+	f func(T, T2) Out,
+) gp.Parser[In, Out] {
+	return gp.Bind(p, func(x T) gp.Parser[In, Out] {
+		return gp.Bind(p2, func(x2 T2) gp.Parser[In, Out] {
+			return gp.Return[In](f(x, x2))
+		})
+	})
+}
+func Seq3[In, Out, T, T2, T3 any](
+	p gp.Parser[In, T],
+	p2 gp.Parser[In, T2],
+	p3 gp.Parser[In, T3],
+	f func(T, T2, T3) Out,
+) gp.Parser[In, Out] {
+	return gp.Bind(p, func(x T) gp.Parser[In, Out] {
+		return gp.Bind(p2, func(x2 T2) gp.Parser[In, Out] {
+			return gp.Bind(p3, func(x3 T3) gp.Parser[In, Out] {
+				return gp.Return[In](f(x, x2, x3))
+			})
+		})
+	})
+}
+func Seq4[In, Out, T, T2, T3, T4 any](
+	p gp.Parser[In, T],
+	p2 gp.Parser[In, T2],
+	p3 gp.Parser[In, T3],
+	p4 gp.Parser[In, T4],
+	f func(T, T2, T3, T4) Out,
+) gp.Parser[In, Out] {
+	return gp.Bind(p, func(x T) gp.Parser[In, Out] {
+		return gp.Bind(p2, func(x2 T2) gp.Parser[In, Out] {
+			return gp.Bind(p3, func(x3 T3) gp.Parser[In, Out] {
+				return gp.Bind(p4, func(x4 T4) gp.Parser[In, Out] {
+					return gp.Return[In](f(x, x2, x3, x4))
+				})
+			})
+		})
+	})
+}
+func Seq5[In, Out, T, T2, T3, T4, T5 any](
+	p gp.Parser[In, T],
+	p2 gp.Parser[In, T2],
+	p3 gp.Parser[In, T3],
+	p4 gp.Parser[In, T4],
+	p5 gp.Parser[In, T5],
+	f func(T, T2, T3, T4, T5) Out,
+) gp.Parser[In, Out] {
+	return gp.Bind(p, func(x T) gp.Parser[In, Out] {
+		return gp.Bind(p2, func(x2 T2) gp.Parser[In, Out] {
+			return gp.Bind(p3, func(x3 T3) gp.Parser[In, Out] {
+				return gp.Bind(p4, func(x4 T4) gp.Parser[In, Out] {
+					return gp.Bind(p5, func(x5 T5) gp.Parser[In, Out] {
+						return gp.Return[In](f(x, x2, x3, x4, x5))
+					})
+				})
+			})
+		})
+	})
+}
+func Seq6[In, Out, T, T2, T3, T4, T5, T6 any](
+	p gp.Parser[In, T],
+	p2 gp.Parser[In, T2],
+	p3 gp.Parser[In, T3],
+	p4 gp.Parser[In, T4],
+	p5 gp.Parser[In, T5],
+	p6 gp.Parser[In, T6],
+	f func(T, T2, T3, T4, T5, T6) Out,
+) gp.Parser[In, Out] {
+	return gp.Bind(p, func(x T) gp.Parser[In, Out] {
+		return gp.Bind(p2, func(x2 T2) gp.Parser[In, Out] {
+			return gp.Bind(p3, func(x3 T3) gp.Parser[In, Out] {
+				return gp.Bind(p4, func(x4 T4) gp.Parser[In, Out] {
+					return gp.Bind(p5, func(x5 T5) gp.Parser[In, Out] {
+						return gp.Bind(p6, func(x6 T6) gp.Parser[In, Out] {
+							return gp.Return[In](f(x, x2, x3, x4, x5, x6))
+						})
+					})
+				})
+			})
+		})
+	})
+}
+func Seq7[In, Out, T, T2, T3, T4, T5, T6, T7 any](
+	p gp.Parser[In, T],
+	p2 gp.Parser[In, T2],
+	p3 gp.Parser[In, T3],
+	p4 gp.Parser[In, T4],
+	p5 gp.Parser[In, T5],
+	p6 gp.Parser[In, T6],
+	p7 gp.Parser[In, T7],
+	f func(T, T2, T3, T4, T5, T6, T7) Out,
+) gp.Parser[In, Out] {
+	return gp.Bind(p, func(x T) gp.Parser[In, Out] {
+		return gp.Bind(p2, func(x2 T2) gp.Parser[In, Out] {
+			return gp.Bind(p3, func(x3 T3) gp.Parser[In, Out] {
+				return gp.Bind(p4, func(x4 T4) gp.Parser[In, Out] {
+					return gp.Bind(p5, func(x5 T5) gp.Parser[In, Out] {
+						return gp.Bind(p6, func(x6 T6) gp.Parser[In, Out] {
+							return gp.Bind(p7, func(x7 T7) gp.Parser[In, Out] {
+								return gp.Return[In](f(x, x2, x3, x4, x5, x6, x7))
+							})
+						})
+					})
+				})
+			})
+		})
+	})
+}
+func Seq8[In, Out, T, T2, T3, T4, T5, T6, T7, T8 any](
+	p gp.Parser[In, T],
+	p2 gp.Parser[In, T2],
+	p3 gp.Parser[In, T3],
+	p4 gp.Parser[In, T4],
+	p5 gp.Parser[In, T5],
+	p6 gp.Parser[In, T6],
+	p7 gp.Parser[In, T7],
+	p8 gp.Parser[In, T8],
+	f func(T, T2, T3, T4, T5, T6, T7, T8) Out,
+) gp.Parser[In, Out] {
+	return gp.Bind(p, func(x T) gp.Parser[In, Out] {
+		return gp.Bind(p2, func(x2 T2) gp.Parser[In, Out] {
+			return gp.Bind(p3, func(x3 T3) gp.Parser[In, Out] {
+				return gp.Bind(p4, func(x4 T4) gp.Parser[In, Out] {
+					return gp.Bind(p5, func(x5 T5) gp.Parser[In, Out] {
+						return gp.Bind(p6, func(x6 T6) gp.Parser[In, Out] {
+							return gp.Bind(p7, func(x7 T7) gp.Parser[In, Out] {
+								return gp.Bind(p8, func(x8 T8) gp.Parser[In, Out] {
+									return gp.Return[In](f(x, x2, x3, x4, x5, x6, x7, x8))
+								})
+							})
+						})
+					})
+				})
+			})
+		})
+	})
+}
+func Seq9[In, Out, T, T2, T3, T4, T5, T6, T7, T8, T9 any](
+	p gp.Parser[In, T],
+	p2 gp.Parser[In, T2],
+	p3 gp.Parser[In, T3],
+	p4 gp.Parser[In, T4],
+	p5 gp.Parser[In, T5],
+	p6 gp.Parser[In, T6],
+	p7 gp.Parser[In, T7],
+	p8 gp.Parser[In, T8],
+	p9 gp.Parser[In, T9],
+	f func(T, T2, T3, T4, T5, T6, T7, T8, T9) Out,
+) gp.Parser[In, Out] {
+	return gp.Bind(p, func(x T) gp.Parser[In, Out] {
+		return gp.Bind(p2, func(x2 T2) gp.Parser[In, Out] {
+			return gp.Bind(p3, func(x3 T3) gp.Parser[In, Out] {
+				return gp.Bind(p4, func(x4 T4) gp.Parser[In, Out] {
+					return gp.Bind(p5, func(x5 T5) gp.Parser[In, Out] {
+						return gp.Bind(p6, func(x6 T6) gp.Parser[In, Out] {
+							return gp.Bind(p7, func(x7 T7) gp.Parser[In, Out] {
+								return gp.Bind(p8, func(x8 T8) gp.Parser[In, Out] {
+									return gp.Bind(p9, func(x9 T9) gp.Parser[In, Out] {
+										return gp.Return[In](f(x, x2, x3, x4, x5, x6, x7, x8, x9))
+									})
+								})
+							})
+						})
+					})
+				})
+			})
+		})
+	})
+}

naive/naive_test.go

@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: Unlicense
+
+package naive_test
+
+import (
+	"testing"
+
+	"git.codemonkeysoftware.net/b/gigaparsec"
+	"git.codemonkeysoftware.net/b/gigaparsec/naive"
+)
+
+func BenchmarkBind5(b *testing.B) {
+	type Bind5T = func(p gigaparsec.Parser[byte, byte], f func(byte) gigaparsec.Parser[byte, byte], f2 func(byte) gigaparsec.Parser[byte, byte], f3 func(byte) gigaparsec.Parser[byte, byte], f4 func(byte) gigaparsec.Parser[byte, byte], f5 func(byte) gigaparsec.Parser[byte, byte]) gigaparsec.Parser[byte, byte]
+
+	f := func(b byte) gigaparsec.Parser[byte, byte] {
+		return gigaparsec.Return[byte](b + 1)
+	}
+	p := func(bind5 Bind5T) gigaparsec.Parser[byte, byte] {
+		// gigaparsec.Bind5()
+		return bind5(gigaparsec.Match(byte(0)), f, f, f, f, f)
+	}
+	input := gigaparsec.SliceReaderAt[byte]{0}
+	b.Run("gigaparsec.Bind5", func(b *testing.B) {
+		for range b.N {
+			gigaparsec.Run(p(gigaparsec.Bind5), input)
+		}
+
+	})
+	b.Run("naïve.Bind5", func(b *testing.B) {
+		for range b.N {
+			gigaparsec.Run(p(naive.Bind5), input)
+		}
+	})
+}
+
+func BenchmarkBind9(b *testing.B) {
+	type Bind9T = func(p gigaparsec.Parser[byte, byte], f func(byte) gigaparsec.Parser[byte, byte], f2 func(byte) gigaparsec.Parser[byte, byte], f3 func(byte) gigaparsec.Parser[byte, byte], f4 func(byte) gigaparsec.Parser[byte, byte], f5 func(byte) gigaparsec.Parser[byte, byte], f6 func(byte) gigaparsec.Parser[byte, byte], f7 func(byte) gigaparsec.Parser[byte, byte], f8 func(byte) gigaparsec.Parser[byte, byte], f9 func(byte) gigaparsec.Parser[byte, byte]) gigaparsec.Parser[byte, byte]
+
+	f := func(b byte) gigaparsec.Parser[byte, byte] {
+		return gigaparsec.Return[byte](b + 1)
+	}
+	p := func(bind5 Bind9T) gigaparsec.Parser[byte, byte] {
+		// gigaparsec.Bind5()
+		return bind5(gigaparsec.Match(byte(0)), f, f, f, f, f, f, f, f, f)
+	}
+	input := gigaparsec.SliceReaderAt[byte]{0}
+	b.Run("gigaparsec.Bind9", func(b *testing.B) {
+		for range b.N {
+			gigaparsec.Run(p(gigaparsec.Bind9), input)
+		}
+
+	})
+	b.Run("naive.Bind9", func(b *testing.B) {
+		for range b.N {
+			gigaparsec.Run(p(naive.Bind9), input)
+		}
+	})
+}
+
+func BenchmarkSeq5(b *testing.B) {
+	type P = gigaparsec.Parser[byte, byte]
+	type Seq5T = func(P, P, P, P, P, func(byte, byte, byte, byte, byte) byte) P
+
+	zero := gigaparsec.Return[byte, byte](0)
+
+	f := func(a, b, c, d, e byte) byte {
+		return a + b + c + d + e
+	}
+	p := func(seq5 Seq5T) P {
+		return seq5(zero, zero, zero, zero, zero, f)
+	}
+	input := gigaparsec.SliceReaderAt[byte]{0}
+	b.Run("gigaparsec.Seq5", func(b *testing.B) {
+		for range b.N {
+			gigaparsec.Run(p(gigaparsec.Seq5), input)
+		}
+	})
+	b.Run("naive.Seq5", func(b *testing.B) {
+		for range b.N {
+			gigaparsec.Run(p(naive.Seq5), input)
+		}
+	})
+}
+
+func BenchmarkSeq9(b *testing.B) {
+	type P = gigaparsec.Parser[byte, byte]
+	type Seq9T = func(P, P, P, P, P, P, P, P, P, func(byte, byte, byte, byte, byte, byte, byte, byte, byte) byte) P
+
+	zero := gigaparsec.Return[byte, byte](0)
+
+	f := func(a, b, c, d, e, f, g, h, i byte) byte {
+		return a + b + c + d + e + f + g + h + i
+	}
+	p := func(seq9 Seq9T) P {
+		return seq9(zero, zero, zero, zero, zero, zero, zero, zero, zero, f)
+	}
+	input := gigaparsec.SliceReaderAt[byte]{0}
+	b.Run("gigaparsec.Seq9", func(b *testing.B) {
+		for range b.N {
+			gigaparsec.Run(p(gigaparsec.Seq9), input)
+		}
+	})
+	b.Run("naive.Seq9", func(b *testing.B) {
+		for range b.N {
+			gigaparsec.Run(p(naive.Seq9), input)
+		}
+	})
+}

parser_test.go

@@ -4,6 +4,8 @@ package gigaparsec_test
 
 import (
 	"bytes"
+	"errors"
+	"fmt"
 	"testing"
 
 	"git.codemonkeysoftware.net/b/gigaparsec"
@@ -125,8 +127,32 @@ func TestSatisfy(t *testing.T) {
 	Todo(t)
 }
 
-func Try(t *testing.T) {
-	Todo(t)
+func TestTry(t *testing.T) {
+	type R = ptest.ForcedResult
+	var cases = []struct{ P, TryP R }{
+		{P: R{Succeed: false, Consume: false}, TryP: R{Succeed: false, Consume: false}},
+		{P: R{Succeed: false, Consume: true}, TryP: R{Succeed: false, Consume: false}},
+		{P: R{Succeed: true, Consume: false}, TryP: R{Succeed: true, Consume: false}},
+		{P: R{Succeed: true, Consume: true}, TryP: R{Succeed: true, Consume: true}},
+	}
+	for _, c := range cases {
+		t.Run(fmt.Sprintf("%+v", c.P), func(t *testing.T) {
+			start := gigaparsec.MakeState(gigaparsec.SliceReaderAt[R]{c.P})
+			result, err := gigaparsec.Try(ptest.ForceResult)(start)
+			succeeded, _, _ := result.Status()
+			must.NoError(t, err)
+			test.EqOp(t, c.TryP.Succeed, succeeded)
+			test.EqOp(t, c.TryP.Consume, result.Consumed())
+		})
+	}
+	t.Run("fails on error", func(t *testing.T) {
+		expectedErr := errors.New("it broke")
+		p := gigaparsec.Try(gigaparsec.Match(byte(0)))
+		result, err := p(gigaparsec.MakeState(ptest.ErrReaderAt(expectedErr)))
+		succeeded, _, _ := result.Status()
+		test.ErrorIs(t, err, expectedErr)
+		test.False(t, succeeded)
+	})
 }
 
 func TestLabel(t *testing.T) {
@@ -138,24 +164,57 @@ func TestEnd(t *testing.T) {
 }
 
 func TestRepeat(t *testing.T) {
-	t.Run("succeeds iff number of successes ≥ minCount", rapid.MakeCheck(func(t *rapid.T) {
-		const good byte = 'o'
-		const bad byte = 'x'
 	const maxParses = 100
-
+	t.Run("succeeds iff number of successes ≥ minCount", rapid.MakeCheck(func(t *rapid.T) {
 		minCount := rapid.IntRange(0, maxParses).Draw(t, "minCount")
 		successes := rapid.IntRange(0, maxParses).Draw(t, "successes")
+		shouldSucceed := successes >= minCount
 
-		input := append(ptest.SliceOfN(good, successes), bad)
-		p := gigaparsec.Repeat(minCount, gigaparsec.Match(good))
-		result, err := p(gigaparsec.MakeState(bytes.NewReader(input)))
+		input := append(ptest.SliceOfN(true, successes), false)
+		p := gigaparsec.Repeat(minCount, gigaparsec.Match(true))
+		result, err := p(gigaparsec.MakeState(gigaparsec.SliceReaderAt[bool](input)))
 
 		must.NoError(t, err)
-		success, _, _ := result.Status()
-		test.EqOp(t, successes >= minCount, success, test.Sprint("expected successes ≥ minCount"))
-	}))
-	t.Run("consumes iff at least one application consumes", Todo)
-	t.Run("fails on error", Todo)
-	t.Run("position is unchanged on failure", Todo)
-	t.Run("position follows last success on overall success", Todo)
+		success, _, next := result.Status()
+		test.EqOp(t, shouldSucceed, success)
+		if success {
+			test.EqOp(t, uint64(successes), next.Pos())
+		}
+	}))
+	t.Run("consumes iff at least one application consumes", rapid.MakeCheck(func(t *rapid.T) {
+		input := rapid.Map(rapid.SliceOfN(rapid.Just(ptest.ForcedResult{Succeed: true}), 0, 100),
+			func(ts []ptest.ForcedResult) []ptest.ForcedResult { return append(ts, ptest.ForcedResult{}) }).Draw(t, "input")
+		consumeAt := rapid.Ptr(rapid.IntRange(0, len(input)-1), true).Draw(t, "consumeAt")
+		if consumeAt != nil {
+			input[*consumeAt].Consume = true
+		}
+		shouldConsume := consumeAt != nil
+
+		result, err := gigaparsec.Repeat(0, ptest.ForceResult)(gigaparsec.MakeState(gigaparsec.SliceReaderAt[ptest.ForcedResult](input)))
+		must.NoError(t, err)
+		test.EqOp(t, shouldConsume, result.Consumed())
+	}))
+
+	t.Run("does not consume on empty input", func(t *testing.T) {
+		p := gigaparsec.Repeat(0, gigaparsec.Match(0))
+		result, err := p(gigaparsec.MakeState(gigaparsec.SliceReaderAt[int](nil)))
+		must.NoError(t, err)
+		must.False(t, result.Consumed())
+	})
+	t.Run("fails on error", func(t *testing.T) {
+		expectedErr := errors.New("it broke")
+		p := gigaparsec.Repeat(0, gigaparsec.Match(byte(0)))
+		result, err := p(gigaparsec.MakeState(ptest.ErrReaderAt(expectedErr)))
+		succeeded, _, _ := result.Status()
+		test.ErrorIs(t, err, expectedErr)
+		test.False(t, succeeded)
+	})
+}
+
+func TestBracket(t *testing.T) {
+	Todo(t)
+}
+
+func TestWhere(t *testing.T) {
+	Todo(t)
 }

seq.go

@@ -205,3 +205,381 @@ func Seq5[In, Out, T, T2, T3, T4, T5 any](
 		return Succeed(anyConsumed, final, next, MessageOK(s.Pos())), nil
 	}
 }
+
+func Seq6[In, Out, T, T2, T3, T4, T5, T6 any](
+	p Parser[In, T],
+	p2 Parser[In, T2],
+	p3 Parser[In, T3],
+	p4 Parser[In, T4],
+	p5 Parser[In, T5],
+	p6 Parser[In, T6],
+	f func(T, T2, T3, T4, T5, T6) Out,
+) Parser[In, Out] {
+	return func(s State[In]) (Result[In, Out], error) {
+		var anyConsumed bool
+		var next = s
+
+		r, err := p(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r.Consumed()
+		success, val, next := r.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r.Message()), nil
+		}
+
+		r2, err := p2(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r2.Consumed()
+		success, val2, next := r2.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r2.Message()), nil
+		}
+
+		r3, err := p3(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r3.Consumed()
+		success, val3, next := r3.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r3.Message()), nil
+		}
+
+		r4, err := p4(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r4.Consumed()
+		success, val4, next := r4.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r4.Message()), nil
+		}
+
+		r5, err := p5(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r5.Consumed()
+		success, val5, next := r5.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r5.Message()), nil
+		}
+
+		r6, err := p6(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r6.Consumed()
+		success, val6, next := r6.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r6.Message()), nil
+		}
+
+		final := f(val, val2, val3, val4, val5, val6)
+		return Succeed(anyConsumed, final, next, MessageOK(s.Pos())), nil
+	}
+}
+
+func Seq7[In, Out, T, T2, T3, T4, T5, T6, T7 any](
+	p Parser[In, T],
+	p2 Parser[In, T2],
+	p3 Parser[In, T3],
+	p4 Parser[In, T4],
+	p5 Parser[In, T5],
+	p6 Parser[In, T6],
+	p7 Parser[In, T7],
+	f func(T, T2, T3, T4, T5, T6, T7) Out,
+) Parser[In, Out] {
+	return func(s State[In]) (Result[In, Out], error) {
+		var anyConsumed bool
+		var next = s
+
+		r, err := p(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r.Consumed()
+		success, val, next := r.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r.Message()), nil
+		}
+
+		r2, err := p2(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r2.Consumed()
+		success, val2, next := r2.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r2.Message()), nil
+		}
+
+		r3, err := p3(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r3.Consumed()
+		success, val3, next := r3.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r3.Message()), nil
+		}
+
+		r4, err := p4(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r4.Consumed()
+		success, val4, next := r4.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r4.Message()), nil
+		}
+
+		r5, err := p5(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r5.Consumed()
+		success, val5, next := r5.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r5.Message()), nil
+		}
+
+		r6, err := p6(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r6.Consumed()
+		success, val6, next := r6.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r6.Message()), nil
+		}
+
+		r7, err := p7(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r7.Consumed()
+		success, val7, next := r7.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r7.Message()), nil
+		}
+
+		final := f(val, val2, val3, val4, val5, val6, val7)
+		return Succeed(anyConsumed, final, next, MessageOK(s.Pos())), nil
+	}
+}
+
+func Seq8[In, Out, T, T2, T3, T4, T5, T6, T7, T8 any](
+	p Parser[In, T],
+	p2 Parser[In, T2],
+	p3 Parser[In, T3],
+	p4 Parser[In, T4],
+	p5 Parser[In, T5],
+	p6 Parser[In, T6],
+	p7 Parser[In, T7],
+	p8 Parser[In, T8],
+	f func(T, T2, T3, T4, T5, T6, T7, T8) Out,
+) Parser[In, Out] {
+	return func(s State[In]) (Result[In, Out], error) {
+		var anyConsumed bool
+		var next = s
+
+		r, err := p(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r.Consumed()
+		success, val, next := r.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r.Message()), nil
+		}
+
+		r2, err := p2(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r2.Consumed()
+		success, val2, next := r2.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r2.Message()), nil
+		}
+
+		r3, err := p3(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r3.Consumed()
+		success, val3, next := r3.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r3.Message()), nil
+		}
+
+		r4, err := p4(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r4.Consumed()
+		success, val4, next := r4.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r4.Message()), nil
+		}
+
+		r5, err := p5(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r5.Consumed()
+		success, val5, next := r5.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r5.Message()), nil
+		}
+
+		r6, err := p6(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r6.Consumed()
+		success, val6, next := r6.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r6.Message()), nil
+		}
+
+		r7, err := p7(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r7.Consumed()
+		success, val7, next := r7.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r7.Message()), nil
+		}
+
+		r8, err := p8(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r8.Consumed()
+		success, val8, next := r8.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r8.Message()), nil
+		}
+
+		final := f(val, val2, val3, val4, val5, val6, val7, val8)
+		return Succeed(anyConsumed, final, next, MessageOK(s.Pos())), nil
+	}
+}
+
+func Seq9[In, Out, T, T2, T3, T4, T5, T6, T7, T8, T9 any](
+	p Parser[In, T],
+	p2 Parser[In, T2],
+	p3 Parser[In, T3],
+	p4 Parser[In, T4],
+	p5 Parser[In, T5],
+	p6 Parser[In, T6],
+	p7 Parser[In, T7],
+	p8 Parser[In, T8],
+	p9 Parser[In, T9],
+	f func(T, T2, T3, T4, T5, T6, T7, T8, T9) Out,
+) Parser[In, Out] {
+	return func(s State[In]) (Result[In, Out], error) {
+		var anyConsumed bool
+		var next = s
+
+		r, err := p(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r.Consumed()
+		success, val, next := r.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r.Message()), nil
+		}
+
+		r2, err := p2(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r2.Consumed()
+		success, val2, next := r2.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r2.Message()), nil
+		}
+
+		r3, err := p3(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r3.Consumed()
+		success, val3, next := r3.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r3.Message()), nil
+		}
+
+		r4, err := p4(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r4.Consumed()
+		success, val4, next := r4.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r4.Message()), nil
+		}
+
+		r5, err := p5(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r5.Consumed()
+		success, val5, next := r5.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r5.Message()), nil
+		}
+
+		r6, err := p6(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r6.Consumed()
+		success, val6, next := r6.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r6.Message()), nil
+		}
+
+		r7, err := p7(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r7.Consumed()
+		success, val7, next := r7.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r7.Message()), nil
+		}
+
+		r8, err := p8(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r8.Consumed()
+		success, val8, next := r8.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r8.Message()), nil
+		}
+
+		r9, err := p9(next)
+		if err != nil {
+			return Result[In, Out]{}, err
+		}
+		anyConsumed = anyConsumed || r9.Consumed()
+		success, val9, next := r9.Status()
+		if !success {
+			return Fail[In, Out](anyConsumed, r9.Message()), nil
+		}
+
+		final := f(val, val2, val3, val4, val5, val6, val7, val8, val9)
+		return Succeed(anyConsumed, final, next, MessageOK(s.Pos())), nil
+	}
+}

state_test.go

@@ -1,18 +1,47 @@
+// SPDX-License-Identifier: Unlicense
+
 package gigaparsec_test
 
 import (
 	"bytes"
+	"cmp"
 	"io"
+	"math"
 	"testing"
 
 	"git.codemonkeysoftware.net/b/gigaparsec"
 	ptest "git.codemonkeysoftware.net/b/gigaparsec/test"
+	"git.codemonkeysoftware.net/b/gigaparsec/test/generator"
 	pgen "git.codemonkeysoftware.net/b/gigaparsec/test/generator"
 	"github.com/shoenig/test"
 	"github.com/shoenig/test/must"
 	"pgregory.net/rapid"
 )
 
+type customEOFReaderAt struct {
+	r             *bytes.Reader
+	eofAtExactFit bool
+}
+
+func newCustomEOFReaderAt(b []byte, eofAtExactFit bool) customEOFReaderAt {
+	return customEOFReaderAt{
+		r:             bytes.NewReader(b),
+		eofAtExactFit: eofAtExactFit,
+	}
+}
+
+func (r customEOFReaderAt) ReadAt(p []byte, off int64) (n int, err error) {
+	n, err = r.r.ReadAt(p, off)
+	if int64(len(p))+off >= r.r.Size() {
+		if r.eofAtExactFit {
+			err = io.EOF
+		} else {
+			err = nil
+		}
+	}
+	return n, err
+}
+
 func TestState(t *testing.T) {
 	t.Run("state reads the same position every time", rapid.MakeCheck(func(t *rapid.T) {
 		data := rapid.SliceOfN(rapid.Byte(), 1, 100).Draw(t, "data")
@@ -29,19 +58,59 @@ func TestState(t *testing.T) {
 		must.NoError(t, err)
 		must.SliceEqOp(t, expected, dst)
 	}))
-	t.Run("Read returns io.EOF iff it overruns source", rapid.MakeCheck(func(t *rapid.T) {
-		data := rapid.SliceOfN(rapid.Byte(), 0, 100).Draw(t, "data")
-		dst := pgen.SliceOfNZero[byte](0, 200).Draw(t, "dst")
-		st := gigaparsec.MakeState(bytes.NewReader(data))
+	t.Run("Read ends before end of source", rapid.MakeCheck(func(t *rapid.T) {
+		src := rapid.SliceOfN(rapid.Byte(), 1, 100).Draw(t, "src")
+		endReadAt := rapid.IntRange(0, len(src)-1).Draw(t, "endReadAt")
+		pos := rapid.Uint64Range(0, uint64(endReadAt)).Draw(t, "pos")
+		dst := pgen.SliceOfNZero[byte](0, endReadAt-int(pos)).Draw(t, "dst")
+		st := gigaparsec.MakeState(bytes.NewReader(src)).At(pos)
 
-		n, _, err := st.Read(dst)
-		t.Logf("n=%d", n)
-		must.EqOp(t, min(len(data), len(dst)), int(n))
-		if len(dst) > len(data) || st.Pos() == uint64(len(data)) {
-			must.ErrorIs(t, err, io.EOF)
-		} else {
-			must.NoError(t, err)
-		}
+		n, next, err := st.At(pos).Read(dst)
+
+		test.EqOp(t, uint64(len(dst)), n)
+		ptest.StateIsAt(t, next, pos+n)
+		test.NoError(t, err)
+		test.SliceEqOp(t, src[pos:pos+n], dst)
+	}))
+	t.Run("Non-empty Read ends at end of source", rapid.MakeCheck(func(t *rapid.T) {
+		readerReturnsEOF := rapid.Bool().Draw(t, "readerReturnsEOF")
+		src := rapid.SliceOfN(rapid.Byte(), 1, 100).Draw(t, "src")
+		dst := pgen.SliceOfNZero[byte](1, len(src)).Draw(t, "dst")
+		pos := uint64(len(src) - len(dst))
+		st := gigaparsec.MakeState(newCustomEOFReaderAt(src, readerReturnsEOF))
+
+		n, next, err := st.At(pos).Read(dst)
+
+		test.EqOp(t, uint64(len(dst)), n)
+		ptest.StateIsAt(t, next, pos+n)
+		test.NoError(t, err)
+		test.SliceEqOp(t, src[pos:pos+n], dst)
+	}))
+	t.Run("Read overruns source", rapid.MakeCheck(func(t *rapid.T) {
+		src := rapid.SliceOfN(rapid.Byte(), 1, 100).Draw(t, "src")
+		pos := rapid.Uint64Range(0, uint64(len(src))-1).Draw(t, "pos")
+		minDstLen := len(src) - int(pos) + 1
+		dst := pgen.SliceOfNZero[byte](minDstLen, minDstLen+10).Draw(t, "dst")
+		st := gigaparsec.MakeState(bytes.NewReader(src)).At(pos)
+
+		n, next, err := st.Read(dst)
+
+		test.EqOp(t, uint64(len(src)), n+pos)
+		ptest.StateIsAt(t, next, pos+n)
+		test.ErrorIs(t, err, io.EOF)
+		test.SliceEqOp(t, src[pos:pos+n], dst[:n])
+	}))
+	t.Run("Read starts after end of source", rapid.MakeCheck(func(t *rapid.T) {
+		src := rapid.SliceOfN(rapid.Byte(), 0, 100).Draw(t, "src")
+		dst := pgen.SliceOfNZero[byte](0, 100).Draw(t, "dst")
+		pos := rapid.Uint64Min(uint64(len(src))).Draw(t, "pos")
+		st := gigaparsec.MakeState(bytes.NewReader(src)).At(pos)
+
+		n, next, err := st.Read(dst)
+
+		test.EqOp(t, 0, n)
+		ptest.StateIsAt(t, next, pos)
+		test.ErrorIs(t, err, io.EOF)
 	}))
 	t.Run("next state reads next input", rapid.MakeCheck(func(t *rapid.T) {
 		const maxLen = 100
@@ -56,14 +125,6 @@ func TestState(t *testing.T) {
 		n, _, _ := next.Read(dst)
 		must.SliceEqOp(t, data[skip:skip+int(n)], dst[:n])
 	}))
-	t.Run("Read returns io.EOF if n is less than requested", rapid.MakeCheck(func(t *rapid.T) {
-		data := rapid.SliceOfN(rapid.Byte(), 0, 100).Draw(t, "data")
-		st := gigaparsec.MakeState(bytes.NewReader(data))
-
-		n, _, err := st.Read(make([]byte, len(data)+1))
-		test.ErrorIs(t, err, io.EOF)
-		test.EqOp(t, len(data), int(n))
-	}))
 	t.Run("At sets state position", rapid.MakeCheck(func(t *rapid.T) {
 		data := rapid.SliceOfN(rapid.Byte(), 1, 100).Draw(t, "data")
 		pos := rapid.Uint64Range(0, uint64(len(data)-1)).Draw(t, "pos")
@@ -93,7 +154,7 @@ func TestState(t *testing.T) {
 	}))
 	t.Run("Read returns an error if the ReaderAt fails", rapid.MakeCheck(func(t *rapid.T) {
 		expectedErr := pgen.Error().Draw(t, "expectedErr")
-		startPos := rapid.Uint64().Draw(t, "startPos")
+		startPos := rapid.Uint64Max(math.MaxInt64).Draw(t, "startPos")
 		dst := pgen.SliceOfNZero[byte](0, 100).Draw(t, "dst")
 		st := gigaparsec.MakeState(ptest.ErrReaderAt(expectedErr)).At(startPos)
 		n, next, err := st.Read(dst)
@@ -102,3 +163,42 @@ func TestState(t *testing.T) {
 		test.Zero(t, n)
 	}))
 }
+
+func TestSliceReaderAt(t *testing.T) {
+	const maxLen = 100
+	t.Run("offset ≥ 0", rapid.MakeCheck(func(t *rapid.T) {
+		src := rapid.SliceOfN(rapid.Byte(), 0, maxLen).Draw(t, "src")
+		dst := generator.SliceOfNZero[byte](0, maxLen).Draw(t, "dst")
+		offset := rapid.Int64Range(0, int64(len(src))+10).Draw(t, "offset")
+
+		n, err := gigaparsec.SliceReaderAt[byte](src).ReadAt(dst, offset)
+
+		switch cmp.Compare(len(src), int(offset)+len(dst)) {
+		case -1:
+			// Read overruns src.
+			test.ErrorIs(t, err, io.EOF)
+			test.EqOp(t, max(0, len(src)-int(offset)), n)
+		case 0:
+			// Read exactly reaches end of source.
+			// io.ReaderAt spec allows error to be either io.EOF or nil.
+			test.EqOp(t, len(dst), n)
+		case 1:
+			// Read ends before end of source.
+			test.NoError(t, err)
+			test.EqOp(t, len(dst), n)
+		}
+
+		if offset < int64(len(src)) {
+			test.SliceEqOp(t, src[offset:offset+int64(n)], dst[:n])
+		}
+	}))
+	t.Run("offset < 0", rapid.MakeCheck(func(t *rapid.T) {
+		src := rapid.SliceOfN(rapid.Byte(), 0, maxLen).Draw(t, "src")
+		dst := generator.SliceOfNZero[byte](0, maxLen).Draw(t, "dst")
+		offset := rapid.Int64Max(-1).Draw(t, "offset")
+
+		n, err := gigaparsec.SliceReaderAt[byte](src).ReadAt(dst, offset)
+		test.Error(t, err)
+		test.EqOp(t, 0, n)
+	}))
+}

test/helpers.go

@@ -4,6 +4,7 @@
 package test
 
 import (
+	"errors"
 	"io"
 
 	"git.codemonkeysoftware.net/b/gigaparsec"
@@ -34,3 +35,22 @@ func SliceOfN[T any](value T, n int) []T {
 	}
 	return s
 }
+
+type ForcedResult struct{ Succeed, Consume bool }
+
+func ForceResult(state gigaparsec.State[ForcedResult]) (gigaparsec.Result[ForcedResult, struct{}], error) {
+	buf := make([]ForcedResult, 1)
+	_, next, err := state.Read(buf)
+	if errors.Is(err, io.EOF) {
+		return gigaparsec.Fail[ForcedResult, struct{}](false, gigaparsec.MessageEnd(state.Pos())), nil
+	}
+	if err != nil {
+		return gigaparsec.Result[ForcedResult, struct{}]{}, err
+	}
+	tok := buf[0]
+	if tok.Succeed {
+		return gigaparsec.Succeed(tok.Consume, struct{}{}, next, gigaparsec.MessageOK(state.Pos())), nil
+	} else {
+		return gigaparsec.Fail[ForcedResult, struct{}](tok.Consume, gigaparsec.MakeMessage(state.Pos(), "Succeed=false", "Succeed=true")), nil
+	}
+}