Exceptions

The CHR runtime system reports instantiation and type errors for the predicates:

find_constraint/2

findall_constraints/3

insert_constraint/2

remove_constraint/1

notify_constrained/1

The only other CHR specific runtime error is:

{CHR ERROR: registering <New>, module <Module> already hosts <Old>}

An attempt to load a second handler New into module <Module> already hosting handler <Old> was made.

The following exceptional conditions are detected by the CHR compiler:

{CHR Compiler ERROR: syntax rule <N>: <Term>}

If the N-th <Term> in the file being loaded violates the CHR syntax (see CHR Syntax).

{CHR Compiler ERROR: too many general heads in <Name>}

Unspecific heads in definitions like C \ C <=> true must not be combined with other heads in rule <Name>.

{CHR Compiler ERROR: bad pragma <Pragma> in <Name>}

The pragma <Pragma> used in rule <Name> does not qualify. Currently this only happens if <Pragma> is unbound.

{CHR Compiler ERROR: found head <F/A> in <Name>, expected one of: <F/A list>}

Rule <Name> has a head of given F/A which is not among the defined constraints.

{CHR Compiler ERROR: head identifiers in <Name> are not unique variables}

The identifiers to refer to individual constraints (heads) via # in rule <Name> do not meet the indicated requirements.

{CHR Compiler ERROR: no handler defined}

CHR specific language elements, declarations or rules for example, are used before a handler was defined. This error is usually reported a couple of times, i.e. as often as there are CHR forms in the file expecting the missing definition.

{CHR Compiler ERROR: compilation failed}

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