parser/parser.go

@@ -37,17 +37,9 @@ func (this *Parser) expect (allowed ...lexer.TokenKind) (lexer.Token, error) {
 	token, err := this.next()
 	if err != nil { return lexer.Token { }, err }
 	if !token.Is(allowed...) {
-		message := "expected"
+		return lexer.Token { }, errors.Errorf (
-		for index, token := range allowed {
+			token.Position, "expected %s",
-			if index > 0 && len(allowed) > 2 {
+			commaList(allowed...))
-				message += ", "
-			}
-			if index == len(allowed) - 1 {
-				message += " or "
-			}
-			message += fmt.Sprintf(" %v", token)
-		}
-		return lexer.Token { }, errors.Errorf(token.Position, message)
 	}
 	return token, nil
 }
@@ -59,11 +51,35 @@ func (this *Parser) expectDesc (description string, allowed ...lexer.TokenKind)
 	token, err := this.next()
 	if err != nil { return lexer.Token { }, err }
 	if !token.Is(allowed...) {
-		return lexer.Token { }, errors.Errorf(token.Position, "expected %s", description)
+		return lexer.Token { }, errors.Errorf (
+			token.Position, "expected %s",
+			description)
 	}
 	return token, nil
 }
 
+// expectValue returns an error if the current token's value does not match the
+// allowed values.
+func (this *Parser) expectValue (allowed ...string) error {
+	if !this.token.ValueIs(allowed...) {
+		return errors.Errorf (
+			this.token.Position, "expected %s",
+			commaList(allowed))
+	}
+	return nil
+}
+
+// expectValueDesc is like expectValue, but the expected value(s) are described
+// manually.
+func (this *Parser) expectValueDesc (description string, allowed ...string) error {
+	if !this.token.ValueIs(allowed...) {
+		return errors.Errorf (
+			this.token.Position, "expected %s",
+			description)
+	}
+	return nil
+}
+
 func (this *Parser) next () (lexer.Token, error) {
 	token, err := this.lexer.Next()
 	if err != nil { return token, err }
@@ -71,16 +87,6 @@ func (this *Parser) next () (lexer.Token, error) {
 	return token, nil
 }
 
-func prependCopy[ELEMENT any] (item ELEMENT, array []ELEMENT) []ELEMENT {
-	return append([]ELEMENT { item }, array...)
-}
-
-func appendCopy[ELEMENT any] (array []ELEMENT, items ...ELEMENT) []ELEMENT {
-	newArray := make([]ELEMENT, len(array) + len(items))
-	copy(newArray[copy(newArray, array):], items)
-	return array
-}
-
 func (this *Parser) parse () error {
 	for {
 		token, err := this.expectDesc (
@@ -94,3 +100,27 @@ func (this *Parser) parse () error {
 	}
 	return nil
 }
+
+func commaList[ELEMENT any] (items ...ELEMENT) string {
+	list := ""
+	for index, item := range items {
+		if index > 0 && len(items) > 2 {
+			list += ", "
+		}
+		if index == len(items) - 1 {
+			list += " or "
+		}
+		list += fmt.Sprintf("%v", item)
+	}
+	return list
+}
+
+func prependCopy[ELEMENT any] (item ELEMENT, array []ELEMENT) []ELEMENT {
+	return append([]ELEMENT { item }, array...)
+}
+
+func appendCopy[ELEMENT any] (array []ELEMENT, items ...ELEMENT) []ELEMENT {
+	newArray := make([]ELEMENT, len(array) + len(items))
+	copy(newArray[copy(newArray, array):], items)
+	return array
+}