Question

This is my arithmetic inequality expression in prolog:

2*X + 3*Y > 4*Z

I used the unity term manipulator like this:

Expr =.. [Op, Lhs, Rhs]

And now I have Lhs = 2*X + 3*Y, Rhs as 4*Z and Op as >
Everything fine till now.

What I want is to construct a delayed goal using the IC library in Eclipse Prolog for this expression.
Example, I want a newly created variable to assigned like this:

Eq = (Lhs #Op Rhs)  %meaning, Eq = (2*X + 3*Y #> 4*Z)

Now, since the required inequality (in this case >), is stored in Op, though I use Eq = (Lhs #Op Rhs), eclipse is returning error.

How do i create this delayed constraint, when my operator is to be taken from the variable Op?
Thank You.

Answer 1

You could use facts to define the relations:

cstr(=,#=).

Or use concat_atom/2:

concat_atom([#,Op],CstrOp),

E.g.:

?- Eq = (X = 1),
   Eq =.. [Op, L, R],
   concat_atom([#, Op], CstrOp),
   Cstr =.. [CstrOp, L, R],
   call(Cstr).
Eq = 1 = 1
X = 1
Op = =
L = 1
R = 1
CstrOp = #=
Cstr = 1 #= 1
Yes (0.00s cpu)

Note that this only works for the basic equality/inequality operators. You cannot add # to just any operator and expect it to work as a constraint!