Creating Predicates

[g0dwyn]

Hey all,

I'm not quite sure if this is the right forum - it's a fairly advanced question, and I'm also not exactly a beginner. Still, I figure here's a decent place to start.

I'd like to be able to create boolean predicates. Not a boolean type, nor a function that returns a boolean - I just want to be able to create a predicate, which can be tested later.

For example, I want to be able to create a predicate (x == y), define x and y upon its creation WITHOUT actually testing to see if x==y, store it in a structure, and then test it when it's called upon. If possible, I'd like to avoid creating a class to encapsulate it, but if there's no other way then I'll do it. Thanks in advance, let me know if you need additional clarification.

[chadder06]

Can you give an example of how you would use such a thing?

[g0dwyn]

I'd use it to test objects in an environment (i.e. check to see if x == y, where x and y are two variables in the environment). However, I'd like the actual predicate that tests x == y to be generated by the code (so it creates x, creates y, and then creates some sort of boolean predicate equal to (x == y). Then I'd like to store the predicate for testing later by some other function.

The (extremely!) pseudo-code would look something like this:

bool p [5];

function makepredicate (x, y) {
  return (x==y)
}

function testpredicate(p) {
  return (test p)
  }

p[0] = makepredicate(x,y)
testpredicate(p[0])

Note that under makepredicate, I don't want to actually return the value of (x==y) - I want to return the actual predicate (x==y). Does this help any? I know this can be done in lisp-family languages, I just want to know if you can do it in C++