Propagate errors through Choose

gigaparsec.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"slices"
 
 	"git.codemonkeysoftware.net/b/gigaparsec/cursor"
 )
@@ -99,6 +100,52 @@ func Choose[In, Out any](p, q Parser[In, Out]) Parser[In, Out] {
 	}
 }
 
+func ChooseMany[In, Out any](p Parser[In, Out], ps ...Parser[In, Out]) Parser[In, Out] {
+	all := append([]Parser[In, Out]{p}, ps...)
+	return func(input State[In]) (bool, 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)
+			if consumed {
+				return consumed, result, err
+			}
+			var qMsg Message
+			if err != nil {
+				var parseErr ParseError
+				if !errors.As(err, &parseErr) {
+					// It broke. Give up.
+					return consumed, result, err
+				}
+				failed = failed && true
+				qMsg = Message(parseErr)
+			} else {
+				if failed {
+					value = result.Value
+					failed = false
+				}
+				qMsg = result.Message
+			}
+			if !gotGot {
+				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 false, Result[In, Out]{
+			Value:   value,
+			State:   input,
+			Message: msg,
+		}, nil
+	}
+}
+
 // Try behaves identically to p, except that if p returns an error,
 // Try will pretend that no input was consumed. This allows infinite
 // lookahead: Since Choose only calls another parser when the previous