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copied!<p>Your problem is in your lexical analyzer (independently of whether there's a problem in your grammar — I've not analyzed the grammar, because I hit on the problem in the lexical analyzer first, and it was sufficient to prevent the grammar working).</p> <p>I added a test <code>main()</code> to <code>lexer.l</code>:</p> <pre><code>%% YYSTYPE yylval; int main(void) { int token; while ((token = yylex()) != 0) printf("Token: %d (%s)\n", token, yytext); return 0; } </code></pre> <p>I then ran it on your sample code to see whether the token stream is generated correctly. The output I got is:</p> <pre><code>TOKEN_BEGIN Token: 258 (begin) WhiteSpaces COMMENT NewLine WhiteSpaces TOKEN_IDENTIFIER Token: 265 (x) WhiteSpaces yytext = = Token: 61 (=) WhiteSpaces TOKEN_VALUE Token: 264 (56) yytext = ; Token: 59 (;) NewLine NewLine WhiteSpaces While Token: 260 (while) WhiteSpaces TOKEN_IDENTIFIER Token: 265 (x) WhiteSpaces TOKEN_OPERATOR Token: 263 (>) WhiteSpaces TOKEN_VALUE Token: 264 (0) WhiteSpaces DO Token: 261 (do) NewLine WhiteSpaces TOKEN_BEGIN Token: 258 (begin) NewLine WhiteSpaces POINT_START Token: 262 (point) WhiteSpaces POINT_DEFINITIONS 15.6 Token: 266 (15.6) WhiteSpaces POINT_DEFINITIONS 78.96 Token: 266 (78.96) ; WhiteSpaces end; end; </code></pre> <p>As you can see, the last token returned to the main program is the 78.96.</p> <p>When you recognize a POINT, you start the state POINT_DEFINITIONS. However, once in that state, you're in that state for ever; you never go back to the INITIAL state. You probably need to add a rule to the POINT_DEFINITIONS start state that recognizes a semicolon and executes <code>BEGIN INITIAL;</code>:</p> <pre><code><POINT_DEFINITIONS>{Semicolon} { printf("Semicolon in POINT_DEFINITION state\n"); BEGIN INITIAL; return *yytext; } </code></pre> <p>With this in place, the tail end of the output is:</p> <pre><code>... TOKEN_BEGIN Token: 258 (begin) NewLine WhiteSpaces POINT_START Token: 262 (point) WhiteSpaces POINT_DEFINITIONS 15.6 Token: 266 (15.6) WhiteSpaces POINT_DEFINITIONS 78.96 Token: 266 (78.96) Semicolon in POINT_DEFINITION state Token: 59 (;) NewLine WhiteSpaces TOKEN_END Token: 259 (end) punctuation: yytext = ; Token: 59 (;) NewLine TOKEN_END Token: 259 (end) punctuation: yytext = ; Token: 59 (;) NewLine </code></pre>

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