Next: Old CL Compatibility, Previous: Efficiency Concerns, Up: Top

## Appendix B Common Lisp Compatibility

Following is a list of all known incompatibilities between this package and Common Lisp as documented in Steele (2nd edition).

Certain function names, such as `member`, `assoc`, and `floor`, were already taken by (incompatible) Emacs Lisp functions; this package appends ‘`*`’ to the names of its Common Lisp versions of these functions.

The word `defun*` is required instead of `defun` in order to use extended Common Lisp argument lists in a function. Likewise, `defmacro*` and `function*` are versions of those forms which understand full-featured argument lists. The `&whole` keyword does not work in `defmacro` argument lists (except inside recursive argument lists).

The `equal` predicate does not distinguish between IEEE floating-point plus and minus zero. The `equalp` predicate has several differences with Common Lisp; see Predicates.

The `setf` mechanism is entirely compatible, except that setf-methods return a list of five values rather than five values directly. Also, the new “`setf` function” concept (typified by `(defun (setf foo) ...)`) is not implemented.

The `do-all-symbols` form is the same as `do-symbols` with no obarray argument. In Common Lisp, this form would iterate over all symbols in all packages. Since Emacs obarrays are not a first-class package mechanism, there is no way for `do-all-symbols` to locate any but the default obarray.

The `loop` macro is complete except that `loop-finish` and type specifiers are unimplemented.

The multiple-value return facility treats lists as multiple values, since Emacs Lisp cannot support multiple return values directly. The macros will be compatible with Common Lisp if `values` or `values-list` is always used to return to a `multiple-value-bind` or other multiple-value receiver; if `values` is used without `multiple-value-...` or vice-versa the effect will be different from Common Lisp.

Many Common Lisp declarations are ignored, and others match the Common Lisp standard in concept but not in detail. For example, local `special` declarations, which are purely advisory in Emacs Lisp, do not rigorously obey the scoping rules set down in Steele's book.

The variable `*gensym-counter*` starts out with a pseudo-random value rather than with zero. This is to cope with the fact that generated symbols become interned when they are written to and loaded back from a file.

The `defstruct` facility is compatible, except that structures are of type `:type vector :named` by default rather than some special, distinct type. Also, the `:type` slot option is ignored.

The second argument of `check-type` is treated differently.