Match arbitrary function

[sidmani]

Is there any way to match a function with a certain number of arguments? Suppose I've defined a binary function sum, is there a way to create a pattern f(a, b) that matches sum(x, y)?

[hbarthels]

You mean a pattern where f is a variable that matches a function symbol, like f_[a_, b_] in Mathematica? Unfortunately, MatchPy doesn't support that yet.

If the functions you are considering are not actually arbitrary, that is, if you have a finite number of them that is known by the time you construct your patterns, you could achieve something similar by constructing one pattern for each function. With many-to-one matching, the performance should still be ok.

[sidmani]

Unfortunately the functions are completely arbitrary. Do you know how I could implement that in MatchPy? How difficult would it be?

[hbarthels]

@wheerd should be able to give you a better answer than me. From the algorithmic point of view, right now I don't see a reason why it should be impossible. I just don't have a good feeling for how much work it would be, and if it would integrate nicely into what we already have.

[wheerd]

Integrating it into the one-to-one matching would be relatively easy, but I don't know about the many-to-one case. My gut feeling is that would be complicated if you want to cover all the and iterate over all possible matches. I can't give much more pointers as I haven't worked on this in three years and my knowledge got a bit rusty.