/****************************************************/ /* File: tiny.y */ /* The TINY Yacc/Bison specification file */ /* Compiler Construction: Principles and Practice */ /* Kenneth C. Louden */ /****************************************************/ %{ #define YYPARSER /* distinguishes Yacc output from other code files */ #include "globals.h" #include "util.h" #include "scan.h" #include "parse.h" #define YYSTYPE TreeNode * static char * savedName; /* for use in assignments */ static int savedLineNo; /* ditto */ static TreeNode * savedTree; /* stores syntax tree for later return */ %} %token IF THEN ELSE END REPEAT UNTIL READ WRITE %token ID NUM %token ASSIGN EQ LT PLUS MINUS TIMES OVER LPAREN RPAREN SEMI %token ERROR %% /* Grammar for TINY */ program : stmt_seq { savedTree = $1;} ; stmt_seq : stmt_seq SEMI stmt { YYSTYPE t = $1; if (t != NULL) { while (t->sibling != NULL) t = t->sibling; t->sibling = $3; $$ = $1; } else $$ = $3; } | stmt { $$ = $1; } ; stmt : if_stmt { $$ = $1; } | repeat_stmt { $$ = $1; } | assign_stmt { $$ = $1; } | read_stmt { $$ = $1; } | write_stmt { $$ = $1; } | error { $$ = NULL; } ; if_stmt : IF exp THEN stmt_seq END { $$ = newStmtNode(IfK); $$->child[0] = $2; $$->child[1] = $4; } | IF exp THEN stmt_seq ELSE stmt_seq END { $$ = newStmtNode(IfK); $$->child[0] = $2; $$->child[1] = $4; $$->child[2] = $6; } ; repeat_stmt : REPEAT stmt_seq UNTIL exp { $$ = newStmtNode(RepeatK); $$->child[0] = $2; $$->child[1] = $4; } ; assign_stmt : ID { savedName = copyString(tokenString); savedLineNo = lineno; } ASSIGN exp { $$ = newStmtNode(AssignK); $$->child[0] = $4; $$->attr.name = savedName; $$->lineno = savedLineNo; } ; read_stmt : READ ID { $$ = newStmtNode(ReadK); $$->attr.name = copyString(tokenString); } ; write_stmt : WRITE exp { $$ = newStmtNode(WriteK); $$->child[0] = $2; } ; exp : simple_exp LT simple_exp { $$ = newExpNode(OpK); $$->child[0] = $1; $$->child[1] = $3; $$->attr.op = LT; } | simple_exp EQ simple_exp { $$ = newExpNode(OpK); $$->child[0] = $1; $$->child[1] = $3; $$->attr.op = EQ; } | simple_exp { $$ = $1; } ; simple_exp : simple_exp PLUS term { $$ = newExpNode(OpK); $$->child[0] = $1; $$->child[1] = $3; $$->attr.op = PLUS; } | simple_exp MINUS term { $$ = newExpNode(OpK); $$->child[0] = $1; $$->child[1] = $3; $$->attr.op = MINUS; } | term { $$ = $1; } ; term : term TIMES factor { $$ = newExpNode(OpK); $$->child[0] = $1; $$->child[1] = $3; $$->attr.op = TIMES; } | term OVER factor { $$ = newExpNode(OpK); $$->child[0] = $1; $$->child[1] = $3; $$->attr.op = OVER; } | factor { $$ = $1; } ; factor : LPAREN exp RPAREN { $$ = $2; } | NUM { $$ = newExpNode(ConstK); $$->attr.val = atoi(tokenString); } | ID { $$ = newExpNode(IdK); $$->attr.name = copyString(tokenString); } | error { $$ = NULL; } ; %% int yyerror(char * message) { fprintf(listing,"Syntax error at line %d: %s\n",lineno,message); fprintf(listing,"Current token: "); printToken(yychar,tokenString); Error = TRUE; return 0; } /* yylex calls getToken to make Yacc/Bison output * compatible with ealier versions of the TINY scanner */ static int yylex(void) { return getToken(); } TreeNode * parse(void) { yyparse(); return savedTree; }