Common Lisp Compatibility Top Porting Common Lisp

Appendix C: Old CL Compatibility

Following is a list of all known incompatibilities between this package and the older Quiroz `cl.el' package.

This package's emulation of multiple return values in functions is incompatible with that of the older package. That package attempted to come as close as possible to true Common Lisp multiple return values; unfortunately, it could not be 100% reliable and so was prone to occasional surprises if used freely. This package uses a simpler method, namely replacing multiple values with lists of values, which is more predictable though more noticeably different from Common Lisp.

The defkeyword form and keywordp function are not implemented in this package.

The member, floor, ceiling, truncate, round, mod, and rem functions are suffixed by `*' in this package to avoid collision with existing functions in Emacs 18 or Emacs 19. The older package simply redefined these functions, overwriting the built-in meanings and causing serious portability problems with Emacs 19. (Some more recent versions of the Quiroz package changed the names to cl-member, etc.; this package defines the latter names as aliases for member*, etc.)

Certain functions in the old package which were buggy or inconsistent with the Common Lisp standard are incompatible with the conforming versions in this package. For example, eql and member were synonyms for eq and memq in that package, setf failed to preserve correct order of evaluation of its arguments, etc.

Finally, unlike the older package, this package is careful to prefix all of its internal names with cl-. Except for a few functions which are explicitly defined as additional features (such as floatp-safe and letf), this package does not export any non-`cl-' symbols which are not also part of Common Lisp.

C.1: The cl-compat package

The CL package includes emulations of some features of the old `cl.el', in the form of a compatibility package cl-compat. To use it, put (require 'cl-compat) in your program.

The old package defined a number of internal routines without cl- prefixes or other annotations. Call to these routines may have crept into existing Lisp code. cl-compat provides emulations of the following internal routines: pair-with-newsyms, zip-lists, unzip-lists, reassemble-arglists, duplicate-symbols-p, safe-idiv.

Some setf forms translated into calls to internal functions that user code might call directly. The functions setnth, setnthcdr, and setelt fall in this category; they are defined by cl-compat, but the best fix is to change to use setf properly.

The cl-compat file defines the keyword functions keywordp, keyword-of, and defkeyword, which are not defined by the new CL package because the use of keywords as data is discouraged.

The build-klist mechanism for parsing keyword arguments is emulated by cl-compat; the with-keyword-args macro is not, however, and in any case it's best to change to use the more natural keyword argument processing offered by defun*.

Multiple return values are treated differently by the two Common Lisp packages. The old package's method was more compatible with true Common Lisp, though it used heuristics that caused it to report spurious multiple return values in certain cases. The cl-compat package defines a set of multiple-value macros that are compatible with the old CL package; again, they are heuristic in nature, but they are guaranteed to work in any case where the old package's macros worked. To avoid name collision with the ``official'' multiple-value facilities, the ones in cl-compat have capitalized names: Values, Values-list, Multiple-value-bind, etc.

The functions cl-floor, cl-ceiling, cl-truncate, and cl-round are defined by cl-compat to use the old-style multiple-value mechanism, just as they did in the old package. The newer floor* and friends return their two results in a list rather than as multiple values. Note that older versions of the old package used the unadorned names floor, ceiling, etc.; cl-compat cannot use these names because they conflict with Emacs 19 built-ins.

Common Lisp Compatibility

Top

Porting Common Lisp