Make UnexpectedError a pointer for consistency.

error.go

@@ -45,16 +45,16 @@ type UnexpectedTokenError struct {
 	at         node
 }
 
-func (u UnexpectedTokenError) Error() string { return FormatError(u) }
+func (u *UnexpectedTokenError) Error() string { return FormatError(u) }
 
-func (u UnexpectedTokenError) Message() string { // nolint: golint
+func (u *UnexpectedTokenError) Message() string { // nolint: golint
 	var expected string
 	if u.at != nil {
 		expected = fmt.Sprintf(" (expected %s)", u.at)
 	}
 	return fmt.Sprintf("unexpected token %q%s", u.Unexpected, expected)
 }
-func (u UnexpectedTokenError) Position() lexer.Position { return u.Unexpected.Pos } // nolint: golint
+func (u *UnexpectedTokenError) Position() lexer.Position { return u.Unexpected.Pos } // nolint: golint
 
 type ParseError struct {
 	Msg string

nodes.go

@@ -382,7 +382,7 @@ func (s *sequence) Parse(ctx *parseContext, parent reflect.Value) (out []reflect
 				return nil, nil
 			}
 			token := ctx.Peek()
-			return out, UnexpectedTokenError{Unexpected: token, at: n}
+			return out, &UnexpectedTokenError{Unexpected: token, at: n}
 		}
 		// Special-case for when children return an empty match.
 		// Appending an empty, non-nil slice to a nil slice returns a nil slice.

parser.go

@@ -244,7 +244,7 @@ func (p *Parser[G]) parseOne(ctx *parseContext, parseNode node, rv reflect.Value
 	}
 	token := ctx.Peek()
 	if !token.EOF() && !ctx.allowTrailing {
-		return ctx.DeepestError(UnexpectedTokenError{Unexpected: token})
+		return ctx.DeepestError(&UnexpectedTokenError{Unexpected: token})
 	}
 	return nil
 }
@@ -262,23 +262,23 @@ func (p *Parser[G]) parseInto(ctx *parseContext, parseNode node, rv reflect.Valu
 	}
 	if pv == nil {
 		token := ctx.Peek()
-		return ctx.DeepestError(UnexpectedTokenError{Unexpected: token})
+		return ctx.DeepestError(&UnexpectedTokenError{Unexpected: token})
 	}
 	return nil
 }
 
 func (p *Parser[G]) rootParseable(ctx *parseContext, parseable Parseable) error {
 	if err := parseable.Parse(ctx.PeekingLexer); err != nil {
 		if err == NextMatch {
-			err = UnexpectedTokenError{Unexpected: ctx.Peek()}
+			err = &UnexpectedTokenError{Unexpected: ctx.Peek()}
 		} else {
 			err = &ParseError{Msg: err.Error(), Pos: ctx.Peek().Pos}
 		}
 		return ctx.DeepestError(err)
 	}
 	peek := ctx.Peek()
 	if !peek.EOF() && !ctx.allowTrailing {
-		return ctx.DeepestError(UnexpectedTokenError{Unexpected: peek})
+		return ctx.DeepestError(&UnexpectedTokenError{Unexpected: peek})
 	}
 	return nil
 }