4.5 Analysing compound terms

Compound terms can be viewed as an array of terms with a name and arity (length). This view is expressed by overloading the [] operator.

A type_error is raised if the argument is not compound and a domain_error if the index is out of range.

In addition, the following functions are defined:

PlTerm PlTerm::operator[](int arg)

If the PlTerm is a compound term and arg is between 1 and the arity of the term, return a new PlTerm representing the arg-th argument of the term. If PlTerm is not compound, a type_error is raised. Id arg is out of range, a domain_error is raised. Please note the counting from 1 which is consistent to Prolog's arg/3 predicate, but inconsistent to C's normal view on an array. See also class PlCompound. The following example tests x to represent a term with first-argument an atom or string equal to gnat.

   ...,
   if ( x[1] == "gnat" )
     ...

const char * PlTerm::name()

Return a const char * holding the name of the functor of the compound term. Raises a type_error if the argument is not compound.

int PlTerm::arity()

Returns the arity of the compound term. Raises a type_error if the argument is not compound.