Syntactic Differences

As programs containing CHRs are no longer compiled by a separate process, the .chr extension is no longer implicitly supported. Files with the .chr extension can still be compiled by explicitly specifying the extension in the compile command, as in ['file.chr']. Associated with this change, there are some changes to the declarations of the .chr format:

• operator/3 does not exist. It is not needed because the standard Prolog op/3 declaration can now handle all operator declarations. Replace all operator/3 with op/3 declarations.
• The other declarations handler constraints option are now handled as normal Prolog declarations, i.e. they must be preceded with :-. This is to conform with standard Prolog syntax.

The syntax for naming a rule has been changed, because the old method (using @ clashes with the use of @ in modules. The new operator for naming rules is ::=. Here is part of the minmax handler in the new syntax:

:- handler minmax.
:- constraints leq/2, neq/2, minimum/3, maximum/3.
:- op(700, xfx, neq).

built_in    ::=  X leq Y <=> ground(X), ground(Y) | X @=< Y.
reflexivity ::=  X leq X <=> true.
...