The OP is likely speaking of "Constraint Logic Programming(CLP)".
The set of CLP languages is generally implemented as a superset or add-on package(s) to a Prolog implementation. For example, SICStus Prolog and SWI-Prolog have CLP modules, e.g.:
To the best of my knowledge the modules are written in Prolog. A look at those links will give you an idea of how CLP is used. There are modules available for CLP(X) where X is one of:
In a sense, yes, these modules are written in Prolog. However, that is not the full story: CLP requires special interface predicates that the underlying Prolog system must provide. You cannot implement CLP "on top" of just any Prolog system with reasonable performance and correctness.
Devising and implementing such suitable interface predicates is quite hard, and only a very small number of Prolog systems have succeeded with this so far.
For example, the SWI interface for CLP is too limited in practice, and its constraint solvers have elementary mistakes also because of the limitations of the interface predicates it provides.
In contrast, SICStus Prolog provides a much more general interface to attributed variables that supports all widely used constraint solvers (finite domains, Boolean variables, rational numbers etc.) with good performance and no known mistakes.
The tutorial you link to has several rather severe shortcomings, and I cannot recommend it for learning CLP(FD). Please see my profile page if you are interested in Prolog resources.
The set of CLP languages is generally implemented as a superset or add-on package(s) to a Prolog implementation. For example, SICStus Prolog and SWI-Prolog have CLP modules, e.g.:
https://sicstus.sics.se/sicstus/docs/3.7.1/html/sicstus_32.h...
http://www.swi-prolog.org/pldoc/man?section=clp
and "Constraint Handling Rules(CHR):
http://www.swi-prolog.org/pldoc/man?section=chr
To the best of my knowledge the modules are written in Prolog. A look at those links will give you an idea of how CLP is used. There are modules available for CLP(X) where X is one of:
B = boolean,
Z = integers,
Q = rational numbers,
R = real(floating point) numbers,
FD = finite domains (see "CLP(FD) Constraint Logic Programming over Finite Domains" http://www.pathwayslms.com/swipltuts/clpfd/clpfd.html )
etc.
One can understand how constraining the domain of interest (reducing the search space) to say, the integers, might make search more efficient.