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POHow do i implement If statement in Flex/bison
 

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  1. POHow do i implement If statement in Flex/bison
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    <p>I dont get the error, please can you help me out, here is the .l and .y file.thanks.</p> <pre><code>%{ #include "ifanw.tab.h" extern int yylval; %} %% "=" { return EQ; } "!=" { return NE; } "&lt;" { return LT; } "&lt;=" { return LE; } "&gt;" { return GT; } "&gt;=" { return GE; } "+" { return PLUS; } "-" { return MINUS; } "*" { return MULT; } "/" { return DIVIDE; } ")" { return RPAREN; } "(" { return LPAREN; } ":=" { return ASSIGN; } ";" { return SEMICOLON; } "IF" { return IF; } "THEN" { return THEN; } "ELSE" { return ELSE; } "FI" { return FI; } "WHILE" { return WHILE; } "DO" { return DO; } "OD" { return OD; } "PRINT" { return PRINT; } [0-9]+ { yylval = atoi(yytext); return NUMBER; } [a-z] { yylval = yytext[0] - 'a'; return NAME; } \ { ; } \n { nextline(); } \t { ; } "//".*\n { nextline(); } . { yyerror("illegal token"); } %% </code></pre> <p>Yacc-file</p> <pre><code>%start ROOT %token EQ %token NE %token LT %token LE %token GT %token GE %token PLUS %token MINUS %token MULT %token DIVIDE %token RPAREN %token LPAREN %token ASSIGN %token SEMICOLON %token IF %token THEN %token ELSE %token FI %token WHILE %token DO %token OD %token PRINT %token NUMBER %token NAME %% ROOT: stmtseq { execute($1); } ; statement: designator ASSIGN expression { $$ = assignment($1, $3); } | PRINT expression { $$ = print($2); } | IF expression THEN stmtseq ELSE stmtseq FI { $$ = ifstmt($2, $4, $6); } | IF expression THEN stmtseq FI { $$ = ifstmt($2, $4, empty()); } | WHILE expression DO stmtseq OD { $$ = whilestmt($2, $4); } ; stmtseq: stmtseq SEMICOLON statement { $$ = seq($1, $3); } | statement { $$ = $1; } ; expression: expr2 { $$ = $1; } | expr2 EQ expr2 { $$ = eq($1, $3); } | expr2 NE expr2 { $$ = ne($1, $3); } | expr2 LT expr2 { $$ = le($1, $3); } | expr2 LE expr2 { $$ = le($1, $3); } | expr2 GT expr2 { $$ = gt($1, $3); } | expr2 GE expr2 { $$ = gt($1, $3); } ; expr2: expr3 { $$ == $1; } | expr2 PLUS expr3 { $$ = plus($1, $3); } | expr2 MINUS expr3 { $$ = minus($1, $3); } ; expr3: expr4 { $$ = $1; } | expr3 MULT expr4 { $$ = mult($1, $3); } | expr3 DIVIDE expr4 { $$ = divide ($1, $3); } ; expr4: PLUS expr4 { $$ = $2; } | MINUS expr4 { $$ = neg($2); } | LPAREN expression RPAREN { $$ = $2; } | NUMBER { $$ = number($1); } | designator { $$ = $1; } ; designator: NAME { $$ = name($1); } ; %% </code></pre> <hr> <p>I have another question, is there a possibility to implement a JMP instruction with flex/bison like in Assembler to go to a label like my example, thanks for your help.</p> <pre><code>:L1 IF FLAG AND X"0001" EVT 23; ELSE WAIT 500 ms; JMP L1; END IF; </code></pre>
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