Why I get sum(<P/3> <P/3>) when I use Show in OZ? - show

Question

I'm learning Oz, and was trying to run an example that I found in a book, it is about to simulate a full adder, but what I get is sum( ), so I do not know where the mistake, I would appreciate your help.
Here is part of the code:
fun {XorG X Y}
fun {$ X Y}
fun {GateLoop X Y}
case X#Y of (X|Xr)#(Y|Yr) then
{X+Y-2*X*Y}|{GateLoop Xr Yr}
end
end
in
thread {GateLoop X Y} end
end
end
proc {FullAdder X Y ?C ?S}
K L M
in
K={AndG X Y}
L={AndG Y Z}
M={AndG X Z}
C={OrG K {OrG L M}}
S={XorG Z {XorG X Y}}
end
declare
X=1|1|0|_
Y=0|1|0|_ C S in
{FullAdder X Y C S}
{Show sum(C S)}
AndG and OrG are similar to XorG.

Answer 1

A full adder has 3 inputs and 2 outputs. Indeed you use Z in the FullAdder function but never declare it. So first add it as an argument. Then you have to define a stream for Z as you did for X and Y. Namely :
declare
X=1|1|0|_
Y=0|1|0|_
Z=1|1|1|_ C S in
{FullAdder X Y Z C S}
{Show sum(C S)}
But your main problem is that your XOR gate function is not well defined. It returns an anonymous function. So a call like {XorG A B} returns a function. A better way to implement logic gates is to use a generic function GateMaker in order not to duplicate code :
fun {GateMaker F}
fun {$ Xs Ys}
fun {GateLoop Xs Ys}
case Xs#Ys of (X|Xr)#(Y|Yr) then
{F X Y}|{GateLoop Xr Yr}
end
end
in
thread {GateLoop Xs Ys} end
end
end
Then you only have to define your gates like this :
AndG = {GateMaker fun {$ X Y} X*Y end}
OrG = {GateMaker fun {$ X Y} X+Y-X*Y end}
XorG = {GateMaker fun {$ X Y} X+Y-2*X*Y end}
...
Once you define the gates correctly your FullAdder should work properly.