Syntax error reporting in calc

examples/calc/calcParser.pds

@@ -1,20 +1,5 @@
 parser: LALR(1)
-terminals:
-    "NUM"
-    "COMMA"
-    "FN"
-    "LPAREN"
-    "RPAREN"
-    "SEMICOLON"
-    "ARROW"
-    "IDENT"
-    "PLUS"
-    "MINUS"
-    "TIMES"
-    "DIVIDE"
-    "EXPONENT"
-    "ASSIGN"
-
+lexesis: calcLexer.lxs
 precedence:
     right "EXPONENT"
     left "TIMES" "DIVIDE"
@@ -29,10 +14,11 @@ grammar:
     <toplevel> ::= <toplevel_expr> "SEMICOLON"    [toplevel]
                  | <functiondef> "SEMICOLON"      [toplevel]
                  | <assign> "SEMICOLON"           [toplevel]
-                 | <error> "SEMICOLON"           [toplevel]
+                 | <toplevel_error> "SEMICOLON"   [toplevel]
               ;
 
-    <toplevel_expr> ::= <expr> [toplevel];
+    <toplevel_expr> ::= <expr>   [toplevel];
+    <toplevel_error> ::= <error> [toplevel];
 
     <expr> ::= <expr> "PLUS" <expr>                      [binop]
              | <expr> "MINUS" <expr>                     [binop]

examples/calc/parser.cpp

@@ -24,10 +24,15 @@ Parser::Token Parser::lex() {
         }
         catch (CalcLexer::NoMatch) {
             std::cerr << "Syntax error: unrecognized token" << std::endl;
+            m_lex.skip(1);
         }
     }
 }
 
+Parser::Value Parser::error(Token, const std::vector<calcParser_Symbol>&) {
+    return nullptr;
+}
+
 Parser::Value Parser::reduce_toplevel(std::deque<Token> subparts) {
     if (subparts.empty()) return nullptr;
     if (subparts[0].symbol == calcParser_Symbol::V_expr) {

examples/calc/parser.h

@@ -19,6 +19,7 @@ class Parser : public calcParser<std::unique_ptr<AST>> {
     protected:
         using Value = std::unique_ptr<AST>;
         Token lex() override;
+        Value error(Token current, const std::vector<calcParser_Symbol>& expected) override;
         Value reduce_arguments(std::deque<Token> subparts) override;
         Value reduce_assign(std::deque<Token> subparts) override;
         Value reduce_binop(std::deque<Token> subparts) override;