HMWK3

Due: 3 Apr 2023, by end of class

  Given the following signature:

  signature SLORP = sig

    datatype ('a,'b) slorp = zip |
                     zap of 'a * 'b * ('a, 'b) slorp
    
    val sameslorp :  ('a,'b) slorp * ('a,'b) slorp -> bool                 
                     
    val taz : ('a,'b) slorp -> ('a  * 'b)

    val tiz : ('a,'b) slorp -> ('a,'b) slorp

    val check: (('a * 'b) -> ('a * 'b) -> bool) -> ('a,'b) slorp -> bool
    
    val twiddle: (('a * 'b) -> ('a * 'b) -> bool) -> ('a,'b) slorp -> ('a,'b) slorp

  end;

  and the following specifications:

taz (zap (x,y,z)) = (x,y)
tiz (zap (x,y,z)) = z

taz (zip) = raise error
tiz (zip) = zip

  check f (twiddle f l) = true

  check f zip = true |
  check f zap(x,y,zip) = true |
  check f zap(x,y,zap(r,s,l)) = (f (x,y) (r,s)) andalso (check f zap(r,s,l))


  Create a structure which implements the signature.   

  Think carefully about what it means for this stuff to work correctly; create test cases which correctly assess whether your code works.  Actually test your code.

  Hand in:
  a) the code
  b) your test cases (sufficient to cover each code path)