Sollya User's Manual

Name:

void the functional result of a side-effect or empty argument resp. the corresponding type

Library names:

sollya_obj_t sollya_lib_void() int sollya_lib_is_void(sollya_obj_t) SOLLYA_EXTERNALPROC_TYPE_VOID

Usage:

void : void | type type

Description:

The variable void represents the functional result of a side-effect or an empty argument. It is used only in combination with the applications of procedures or identifiers bound through externalproc to external procedures.

The void result produced by a procedure or an external procedure is not printed at the prompt. However, it is possible to print it out in a print statement or in complex data types such as lists.

The void argument is implicit when giving no argument to a procedure or an external procedure when applied. It can nevertheless be given explicitly. For example, suppose that foo is a procedure or an external procedure with a void argument. Then foo() and foo(void) are correct calls to foo. Here, a distinction must be made for procedures having an arbitrary number of arguments. In this case, an implicit void as the only parameter to a call of such a procedure gets converted into an empty list of arguments, an explicit void gets passed as-is in the formal list of parameters the procedure receives.
void is used also as a type identifier for externalproc. Typically, an external procedure taking void as an argument or returning void is bound with a signature void -> some type or some type -> void. See externalproc for more details.

Example 1:

   > print(void);
   void
   > void;

Example 2:

   > hey = proc() { print("Hello world."); };
   > hey;
   proc()
   {
   print("Hello world.");
   return void;
   }
   > hey();
   Hello world.
   > hey(void);
   Hello world.
   > print(hey());
   Hello world.
   void

Example 3:

   > bashexecute("gcc -fPIC -Wall -c externalprocvoidexample.c");
   > bashexecute("gcc -fPIC -shared -o externalprocvoidexample externalprocvoidexample.o");
   > externalproc(foo, "./externalprocvoidexample", void -> void);
   > foo;
   foo
   > foo();
   Hello from the external world.
   > foo(void);
   Hello from the external world.
   > print(foo());
   Hello from the external world.
   void

Example 4:

   > procedure blub(L = ...) { print("Argument list:", L); };
   > blub(1);
   Argument list: [|1|]
   > blub();
   Argument list: [| |]
   > blub(void);
   Argument list: [|void|]