Control structures are a characteristic of a programming language. Such structures make it possible to repeat one or multiple instructions depending on a condition or a value. BLOCK has to be replaced by a sequence of instructions. ASSIGNMENT has to be replaced by an assignment operation and EXPRESSION by an expression. It is also possible to branch within a program with the help of such control structures:
if EXPRESSION then BLOCK endif
if EXPRESSION then BLOCK else BLOCK endif
for ASSIGNMENT to EXPRESSION do BLOCK endfor
while EXPRESSION do BLOCK endwhile
repeat BLOCK until EXPRESSION