55 lines
1.0 KiB
Plaintext
55 lines
1.0 KiB
Plaintext
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%{
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%}
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%token NUM
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%left '+' '-'
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%left '*' '/'
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%%
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exp : NUM { $$.ival = $1.ival; }
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| exp '+' exp { $$.ival = $1.ival + $3.ival; }
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| exp '-' exp { $$.ival = $1.ival - $3.ival; }
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| exp '*' exp { $$.ival = $1.ival * $3.ival; }
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| exp '/' exp { $$.ival = $1.ival / $3.ival; }
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| '(' exp ')' { $$.ival = $2.ival; }
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;
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%%
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private String buf;
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private void yyerror(String s) {
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throw new RuntimeException("Parse error: " + s);
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}
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private int yylex() {
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if (buf.isEmpty()) {
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return 0;
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}
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int ch = buf.charAt(0);
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buf = buf.substring(1);
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if (ch >= '0' && ch <= '9') {
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yylval.ival = ch - '0';
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while (!buf.isEmpty() && buf.charAt(0) >= '0' && buf.charAt(0) <= '9') {
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yylval.ival = yylval.ival * 10 + buf.charAt(0) - '0';
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buf = buf.substring(1);
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}
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return NUM;
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}
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return ch;
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}
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private int parse(String expr) {
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buf = expr;
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yyparse();
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return val_pop().ival;
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}
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public static void main(String args[])
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{
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Parser par = new Parser(true);
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int res = par.parse(args[0]);
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System.out.println("RESULT is: " + res);
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}
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