Implementing Alternation

There is no explicit support for alternation in assembly language. You must do it in pieces, as in the following:

        ...                #   
if:     beq  $8,$9,else    # branch if equal
        nop                # branch delay slot
        ...                #  
        ...                #   false branch
        ...                #  
        j    endif
        nop
else:   ...                #
        ...                #   true branch
        ...                #
endif:  add   $10,$10,$11  # always executed

This is just an example, not the only way alternation is done. The true branch can come first, if that is more convenient. Conceptually, the branch chosen depends on the outcome of a true/false condition. In implementation, the condition might involve several branch and other instructions.