TRAMPOLINE(3)						     Library Functions Manual						     TRAMPOLINE(3)

NAME

       trampoline - closures as first-class C functions

SYNOPSIS

       #include <trampoline_r.h>

       function = alloc_trampoline_r(address, data0, data1);

       free_trampoline_r(function);

       is_trampoline_r(function)
       trampoline_r_address(function)
       trampoline_r_data0(function)
       trampoline_r_data1(function)

DESCRIPTION

       These  functions  implement closures as first-class C functions.  A closure consists of a regular C function and a piece of data which gets
       passed to the C function when the closure is called.

       Closures as first-class C functions means that they fit into a function pointer and can be called exactly like any other C function.  func-
       tion = alloc_trampoline_r(address, data0, data1) allocates a closure. When function gets called, it stores in a special "lexical chain reg-
       ister" a pointer to a storage area containing data0 in its first word and data1 in its second word and calls the  C  function  at  address.
       The  function at address is responsible for fetching data0 and data1 off the pointer. Note that the "lexical chain register" is a call-used
       register, i.e. is clobbered by function calls.

       This is much like gcc's local functions, except that the GNU C local functions have dynamic extent (i.e. are deallocated when the  creating
       function  returns),  while  trampoline provides functions with indefinite extent: function is only deallocated when free_trampoline_r(func-
       tion) is called.

       is_trampoline_r(function) checks whether the C function function was produced by a call to alloc_trampoline_r.  If this returns	true,  the
       arguments given to alloc_trampoline_r can be retrieved:

	   trampoline_r_address(function) returns address,

	   trampoline_r_data0(function) returns data0,

	   trampoline_r_data1(function) returns data1.

SEE ALSO

       trampoline(3), gcc(1), varargs(3)

PORTING

       The way gcc builds local functions is described in the gcc source, file gcc-2.6.3/config/cpu/cpu.h.

AUTHOR

       Bruno Haible <bruno@clisp.org>

ACKNOWLEDGEMENTS

       Many ideas were cribbed from the gcc source.

								  22 October 1997						     TRAMPOLINE(3)