Add literal pattern syntax and change tree structure syntax

- Literal patterns don't interpret the special characters of regular expressions.
  In other words, 'abc|def' matches only `abc|def`, not `abc` or `def`.
- Change tree structure syntax from '(...) to #(...).

1 files changed, 17 insertions, 1 deletions

diff --git a/spec/lexer.go b/spec/lexer.go
index 1f8805a..1f50a27 100644
--- a/spec/lexer.go
+++ b/spec/lexer.go
@@ -210,9 +210,25 @@ func (l *lexer) lexAndSkipWSs() (*token, error) {
 					Row:   l.row,
 				}
 			case "terminal_close":
-				return newTerminalPatternToken(b.String(), newPosition(l.row)), nil
+				pat := b.String()
+				if pat == "" {
+					return nil, &verr.SpecError{
+						Cause: synErrEmptyPattern,
+						Row:   l.row,
+					}
+				}
+				return newTerminalPatternToken(pat, newPosition(l.row)), nil
+			}
+		}
+	case "literal_pattern":
+		pat := strings.Trim(tok.Text(), "'")
+		if pat == "" {
+			return nil, &verr.SpecError{
+				Cause: synErrEmptyPattern,
+				Row:   l.row,
 			}
 		}
+		return newTerminalPatternToken(mlspec.EscapePattern(pat), newPosition(l.row)), nil
 	case "colon":
 		return newSymbolToken(tokenKindColon, newPosition(l.row)), nil
 	case "or":