[squeakdev] [ANN] Prolog update
Stéphane Rollandin
lecteur at zogotounga.net
Tue Oct 4 22:13:58 UTC 2022
> Could this be easily done using Prolog?
Very easily. Prolog is the king of patternmatching!
For example, the append/2 predicate is implemented as
logicAppend
append([], X, X).
append([H  X], Y, [H  Z]) : append(X, Y, Z).
and this is the *actual code* for the method #logicAppend in class Prolog.
Now equipped with this, you can do
append([a, b], [c, d], List)
and you will get the unification (Prolog's ubernotion for patternmatching)
List = [a,b,c,d].
So far, so good. But you can also do
append(A, B, [1, 2])
which will give you the three ways two lists A and B can be appended to
get [1,2]. The answer will be
A = []. B = [1,2].
A = [1]. B = [2].
A = [1 2]. B= [].
But there is more. You can in fact use any pattern in the arguments, and
unification will tell you what works.
For example,
append([X  T], [a], [Z, Z, Z])
will give you the only way it is possible to append [a] to some [X  T]
(that's a cons cell with car X and cdr T) and get some [Z, Z, Z] as
result (note that only the capitalized terms are variables). It is:
X = a. T = [a]. Z = a
The code snippets above can be directly tested in the REPL you get by
evaluating
Prolog new openGui
Best,
Stef
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