10          else (ALT (r1s, r2s), F_ALT(f1s, f2s)) 

    10          else (ALT (r1s, r2s), F_ALT(f1s, f2s)) 

    11     }

    11     }

    12   }

    12   }

    13   ...

    13   ...

    14 }

    14 }

    16 def F_RIGHT(f: Val => Val) = (v:Val) => Right(f(v))

    15 def F_RIGHT(f: Val => Val) = (v:Val) => Right(f(v))

    17 def F_LEFT(f: Val => Val) = (v:Val) => Left(f(v))

    16 def F_LEFT(f: Val => Val) = (v:Val) => Left(f(v))

    18 def F_ALT(f1: Val => Val, f2: Val => Val) = 

    17 def F_ALT(f1: Val => Val, f2: Val => Val) = 

    19   (v:Val) => v match {

    18   (v:Val) => v match {

    20     case Right(v) => Right(f2(v))

    19     case Right(v) => Right(f2(v))