more precise diagnostic for IF/THEN syntax errors

src/grammar.js

@@ -103,8 +103,8 @@ var statement = optional(or(
                  ));
 var statementSequence = and(statement, repeat(and(";", statement)));
 
-var ifStatement = and("IF", context(expression, Context.If), "THEN", statementSequence
-                    , repeat(and("ELSIF", context(expression, Context.ElseIf), "THEN", statementSequence))
+var ifStatement = and("IF", context(expression, Context.If), required("THEN", "THEN expected"), statementSequence
+                    , repeat(and("ELSIF", context(expression, Context.ElseIf), required("THEN", "THEN expected"), statementSequence))
                     , optional(and("ELSE", context(statementSequence, Context.Else)))
                     , emit("END", Context.emitIfEnd));
 

test/test_unit.js

@@ -767,7 +767,9 @@ var testSuite = {
          ["IF b1 THEN i1 := 0 ELSIF i1 THEN i1 := 2 END",
           "'BOOLEAN' expression expected, got 'INTEGER'"],
          ["IF p THEN i1 := 0 END",
-          "'BOOLEAN' expression expected, got 'POINTER TO anonymous RECORD'"])
+          "'BOOLEAN' expression expected, got 'POINTER TO anonymous RECORD'"],
+         ["IF b1 (*THEN*) i1 := 0 END", "THEN expected"],
+         ["IF b1 THEN i1 := 0 ELSIF ~b1 (*THEN*) i1 := 0 END", "THEN expected"])
     ),
 "CASE statement": testWithContext(
     context(Grammar.statement,