I suspect that someone has already done this: A Haskell library which solves a system of simple equations, where it is only necessary to derive a value from an equation where all but one variables are determined. Say 1+2=x -- add 1 2 x y*z=20 -- times y z 20 x+y=5 -- add x y 5 should be solved as x=3 y=2 z=10 Of course, it is easy to do this for a finite number of variables and equations by assigning integer identifiers to the variables, then scanning the equations repeatedly until all determinable variables are determined. However, imagine I have an infinite number of equations and an infinite number of variables, say 1=x0 -- equal 1 x0 2*x0=x1 -- times 2 x0 x1 2*x1=x2 -- times 2 x1 x2 2*x2=x3 -- times 2 x2 x3 ... Accessing variable values by integer identifiers means that the garbage collector cannot free values that are no longer needed. Thus I thought about how to solve the equations by lazy evaluation. Maybe it is possible to ty the knot this way let (_,_,x0) = add 1 2 x (y0,z0,_) = times y z 20 (x1,y1,_) = add x y 5 x = alternatives [x0,x1] y = alternatives [y0,y1] z = alternatives [z0] in (solve x, solve y, solve z) Independent from the question of how to implement 'alternatives' and 'solve' I wonder if there is a less cumbersome way to do this kind of logic programming in Haskell.