Maude-help mailing list

["Francesoc Bongiovanni" <bongiovanni AT gmail.com>]

Hi there,

I am playing a bit with Maude and trying to implement the filter higher order
function based on some code for the MAP function I found on this archive a
long time ago.

fmod AP{X :: TRIV, Y :: TRIV} is
*** one param function
  sort Func{X,Y} .
  op _[_] : Func{X,Y} X$Elt -> Y$Elt [prec 17] .
*** no param function
  sort FFunc{X} .
  op _[] : FFunc{X} -> X$Elt [prec 17] .
endfm


fmod FILTER{X :: TRIV, Y :: TRIV} is
    inc AP{X,Y} .
    inc BOOL .
    pr LIST{X} .
    pr LIST{Y} .

    var E : X$Elt .
    var L : List{X} .
    var F : Func{X,Y} .

    op filter : List{X} Func{X,Y} -> List{Y} .
    eq filter(nil, F) = nil .
   ceq filter(E L, F) = E  filter(L, F) if F[E] == true .

endfm

When I load the module, the interpreter does not expect E there...why? what I
am missing ?

Thanks in advance for your insights

- Francesco