Rename SpotReader, remove cruft, and move helpers

gigaparsec.go

@@ -0,0 +1,96 @@
+package gigaparsec
+
+import (
+	"errors"
+	"fmt"
+)
+
+// TODO Everything. See https://smunix.github.io/dev.stephendiehl.com/fun/002_parsers.html.
+
+var ErrNoParse = errors.New("no parse")
+
+type Result[T any] struct {
+	Value T
+	State
+	Message
+}
+
+type Message struct {
+	Pos
+	Msg      string
+	Expected []string
+}
+
+type ParseError struct {
+	Message
+}
+
+func (pe ParseError) Error() string {
+	return fmt.Sprintf("parse error: %d: %s", pe.Message.Pos, pe.Message.Msg)
+}
+
+type Pos uint64
+
+type State struct {
+	Pos
+	Input []byte
+}
+
+type Parser[T any] func(State) (consumed bool, reply Result[T], err error)
+
+func Return[T any](value T) Parser[T] {
+	return func(state State) (bool, Result[T], error) {
+		return false, Result[T]{Value: value, State: state}, nil
+	}
+}
+
+func Satisfy(pred func(byte) bool) Parser[byte] {
+	return func(state State) (bool, Result[byte], error) {
+		if len(state.Input) == 0 {
+			return false, Result[byte]{}, ErrNoParse
+		}
+		b := state.Input[0]
+		if pred(b) {
+			return true, Result[byte]{Value: b, State: state.Input[1:]}, nil
+		}
+		return false, Result[byte]{}, ErrNoParse
+	}
+}
+
+func Bind[A, B any](p Parser[A], f func(A) Parser[B]) Parser[B] {
+	return func(input State) (bool, Result[B], error) {
+		consumed, replyA, err := p(input)
+		if err != nil {
+			return false, Result[B]{}, err
+		}
+		consumed2, replyB, err := f(replyA.Value)(replyA.Rest)
+		return consumed || consumed2, replyB, err
+	}
+}
+
+func Choose[A any](p, q Parser[A]) Parser[A] {
+	return func(input State) (bool, Result[A], error) {
+		consumedP, replyP, errP := p(input)
+		if consumedP {
+			return consumedP, replyP, errP
+		}
+		if errP != nil {
+			return q(input)
+		}
+		consumedQ, replyQ, errQ := q(input)
+		if consumedQ {
+			return consumedQ, replyQ, errQ
+		}
+		return consumedP, replyP, errP
+	}
+}
+
+func Try[A any](p Parser[A]) Parser[A] {
+	return func(input State) (bool, Result[A], error) {
+		consumed, reply, err := p(input)
+		if err != nil {
+			return false, Result[A]{}, err
+		}
+		return consumed, reply, err
+	}
+}