Q17

The syntax of the repeat-until statement is given by the following grammar $S \rightarrow\text{ repeat }S_1\text{ until }E$ where E stands for expressions, $S$ and $S_1$ stand for statements. The non-terminals $S$ and $S_1$ have an attribute code that represents generated code. The non-terminal E has two attributes. The attribute code represents generated code to evaluate the expression and store its value in a distinct variable, and the attribute varName contains the name of the variable in which the truth value is stored. The truth-value stored in the variable is 1 if E is true, 0 if E is false. Give a syntax-directed definition to generate three-address code for the repeat-until statement. Assume that you can call a function newlabel() that returns a distinct label for a statement. Use the operator '\\' to concatenate two strings and the function gen(s) to generate a line containing the string s.