1 files changed, 10 insertions, 3 deletions
diff --git a/src/frontend/lexer.l b/src/frontend/lexer.l
index 5b72086..40f6196 100644
--- a/src/frontend/lexer.l
+++ b/src/frontend/lexer.l
@@ -9,7 +9,8 @@
 %option yylineno
 
 DIGIT    [0-9]
-ALPHA    [[:alpha:]_]
+PREID    [a-zA-Z_]
+PSTID    [a-zA-Z0-9_]
 
 /*** rules section ***/
 %%
@@ -30,12 +31,18 @@ ALPHA    [[:alpha:]_]
 "void"          {return VOID;}
 "return"        {return RET;}
 
-{DIGIT}+        {yylval.ival = atol(yytext); return NUMBER;}
-{ALPHA}+        {
+{PREID}{PSTID}* {
   yylval.sval = strdup(yytext);
   return WORD;
        }
 
+{DIGIT}+        {yylval.ival = atol(yytext); return NUMBER;}
+
+{PSTID}+ {
+  printf("Error at line %d: invalid identifier \"%s\"\n", yylineno, yytext);
+  return YYerror;
+}
+
 [[:space:]]+    {/* discard */}
 .               {
   printf("Error at line %d: unrecognized symbol \"%s\"\n", yylineno, yytext);