REQUIRE-PATHNAME-DEFAULTSPROVIDE and REQUIRE are a dual-purpose pair of functions that attempt to provide multi-file Common Lisp programs with a single mechanism to detect and correct incorrect load sequences. These functions were also designed to be used for general file inclusion in Common Lisp. Unfortunately, the file loading feature of REQUIRE is specified such that it is inherently non-portable and environment dependent.PROVIDE, REQUIRE, and *MODULES* from the Common Lisp standard.PROVIDE 'fft)
Would not be Common Lisp.
(REQUIRE 'fft)
Would not be Common Lisp.
REQUIRE is non-portable. The remaining functionality of PROVIDE and REQUIRE (pushing and testing *MODULES*) can easily be implemented by user code. Since some implementations will retain the automatic module loading features of REQUIRE and some won't, use of REQUIRE will almost always make code less portable.REQUIRE. In general, the Lisp Machine implementations invoke the system module building/loading facility while the Unix implementations simply try to load a file in the current directory.PROVIDE and REQUIRE to their package for implementation extensions and change their documentation to indicate that PROVIDE and REQUIRE are non-standard. This is a fairly small change.PROVIDE and REQUIRE will probably be unaffected since implementations will probably maintain their existing functionality. Since the current behavior is decidedly non-portable, portable programs have to aviod or special-case PROVIDE and REQUIRE anyway.PROVIDE and REQUIRE will continue as impediments to portability.PROVIDE and REQUIRE will be made obvious.PROVIDE and REQUIRE to the portable subset of their functionality. This failed because several implementors objected that it compelled them to significantly reduce the functionality they provided users in order to create a trivial feature which any user could easily write for herself.
Fahlman, Gregor, Grey, Loosemore, Moon, Pierson, Pitman, Steele, and Zacharias have expressed support for removing PROVIDE and REQUIRE from the language, at least as the lesser of several evils.
JonL would much rather see PROVIDE and REQUIRE remain in the language as a safety net behind any implementation-specific system building facility. Pierson likes the safety net idea, but doesn't think it's workable without forbidding REQUIRE from loading files.
Pitman suggested that PROVIDE and REQUIRE should be depricated rather than removed entirely. Pierson agrees, but notes that Larry wants us to deal with deprication versus elimination as a separate global topic.
Several people have expressed a desire not to break existing user code. If accepted, this proposal should not break existing code because all implementations are expected to retain their current PROVIDE and REQUIRE functionality as an extension to Common Lisp.