You can test whether a name has been assigned to a procedure as follows:
> example := proc( ) # an empty procedure > end: > type(example, procedure);A valid Darwin name has type name.
> type(example, name); > type(a_valid_Darwin_name, name);An unevaluated procedure call has type uneval. The spirit of uneval comes from the fact that objects of this type ``look like'' procedure calls. The difference between objects of type procedure and type uneval is that the former evaluates while the latter does not.
Recall that there are two ways a procedure call will remain unevaluated in Darwin: either the procedure name is wrapped in a noeval command or the name is undefined in the environment.
> z := noeval(example()); > type(z, uneval); > type(any_undefined_name(), uneval);
An object has type structure if it is either a built-in Darwin structured type or it is of type uneval.
> type(Gene, structure); # the built-in structured type to hold a gene > type(Tree, structure); # the built-in structured type to hold a tree > type(MultiAlign, structure); # the built-in structured type to hold a multiple alignment > x := new_type(); # x is a variable of a new user defined type > type( x, uneval ); # therefore it has type uneval > type( x, structure ); # and type structure
If we create a new structured type such as NewStruct and a variable of this type
> x := NewStruct(a, 5, {1, 2, 3});
the type of x is only the general class noeval. We can
explicitly make NewStruct a structured type recognized by
Darwin by assigning the type name NewStruct the specification as
an unevaluated function of type anything.> NewStruct_type := specuneval(anything, NewStruct);Now we may test whether the type of x is NewStruct.
> type(x, NewStruct);We could encode stricter type checking into NewStruct by replacing the anything declaration in the specuneval command with a sequence of types.
> NewStruct_type := specuneval(string, integer, set, NewStruct);