2.7 Invoking Generic Functions

When a variable with a generic function definition appears as the first element of a list that is being evaluated, the Guile evaluator tries to apply the generic function to the arguments obtained by evaluating the remaining elements of the list. [ *fixme* How do I put this in a more Schemely and less Lispy way? ]

Usually a generic function contains several method definitions, with varying degrees of formal parameter specialization (see section define-method). So it is necessary to sort these methods by specificity with respect to the supplied arguments, and then apply the most specific method definition. Less specific methods may be applied subsequently if a method that is being applied calls next-method.

2.7.1 Determining Which Methods to Apply
2.7.2 Handling Invocation Errors

2.7.1 Determining Which Methods to Apply

[ *fixme* Sorry - this is the area of GOOPS that I understand least of all, so I'm afraid I have to pass on this section. Would some other kind person consider filling it in? ]

generic: apply-generic

method: apply-generic (gf <generic>) args

generic: compute-applicable-methods

method: compute-applicable-methods (gf <generic>) args

generic: sort-applicable-methods

method: sort-applicable-methods (gf <generic>) methods args

generic: method-more-specific?

method: method-more-specific? (m1 <method>) (m2 <method>) args

generic: apply-method

method: apply-method (gf <generic>) methods build-next args

generic: apply-methods

method: apply-methods (gf <generic>) (l <list>) args

2.7.2 Handling Invocation Errors

generic: no-method

method: no-method (gf <generic>) args

When an application invokes a generic function, and no methods at all have been defined for that generic function, GOOPS calls the no-method generic function. The default method calls goops-error with an appropriate message.

generic: no-applicable-method

method: no-applicable-method (gf <generic>) args

When an application applies a generic function to a set of arguments, and no methods have been defined for those argument types, GOOPS calls the no-applicable-method generic function. The default method calls goops-error with an appropriate message.

generic: no-next-method

method: no-next-method (gf <generic>) args

When a generic function method calls (next-method) to invoke the next less specialized method for that generic function, and no less specialized methods have been defined for the current generic function arguments, GOOPS calls the no-next-method generic function. The default method calls goops-error with an appropriate message.