Accessing
- Browsable repository: https://github.com/nklein/list-types
Overview
I often find myself wanting to declare a type as a list of integers or a list of symbols or some such thing. My natural inclination is to do this:
`(or null
(cons ,type (list-of ,type))))
However, the Common Lisp spec requires that all type declaration expansions terminate. As such, one has to hop through various hoops to use a SATISFIES clause in a DEFTYPE to do that. This package wraps that technique and defines the types:
(sequence-of* &optional (type '*))
(sequence-of+ &optional (type '*))
(list-of &optional (type '*) (min-elements '*) (max-elements '*))
(list-of* &optional (type '*))
(list-of+ &optional (type '*))
Additionally, this package also exports the ALEXANDRIA types for PROPER-LIST and CIRCULAR-LIST.
The MIN-ELEMENTS and MAX-ELEMENTS can be either a non-negative integer or the symbol *.
There is no attempt to ensure that a specified MIN-ELEMENTS is less than MAX-ELEMENTS.
Note: there is currently no support for CIRCULAR-LIST-OF.
Unfortunately
Unfortunately, this is not sufficient unless your code gets recompiled every time. If you have a block of code like this:
(check-type bar (list-of+ integer))
...)
This will work when you compile and load it. It will not work when you just load it because at compile time, the expansion of list-of+ created a predicate that will not be there if you just load the compiled check-type into a clean image.
The ugly workaround for this is to use one of the macros before the check-type:
(min-elements '*)
(max-elements '*))
(ensure-sequence-type* &optional (type '*))
(ensure-sequence-type+ &optional (type '*))
So, your code will look like one of the following:
(defun foo (bar)
(check-type bar (list-of+ integer))
...)
;;; Or
(defun foo (bar)
(ensure-sequence-type+ integer)
(check-type bar (list-of+ integer))
...)