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#+BEGIN_SRC Long time ago, in a galaxy far far away...

It is a period of a civil war. Lisp-2 aliens, striking from the function namespace, have fought for the design of their language against lisp-1. #+END_SRC

tl;dr; → skip to API definition https://github.com/guicho271828/lisp-namespace#macro-define-namespace

• update (2016/5/14) : added support for documentation and describe.
• update (2016/5/21) : works on ECL, CLISP, ABCL and CMUCL.

• Introduction

However, destructuring is merely

a syntax sugar for writing the accessor.

There are several libraries which extends =let=. To my knowledge, most of them goes toward destructuring, e.g., allowing =&some-fancy-directive= in the argument list. However, destructuring is now obsolete: superseded by pattern-matching (e.g. fare-matcher, optima, trivia), which cleanly combines =cond=, =typecase=, destructuring and constructors[1]. Now it comes to my mind: what could be the orthogonal aspect that could be combined with =let=, or, =let + cond = pattern matching= ?

Then I noticed an oddness in flet, macrolet, labels, let, symbol-macrolet. Pattern matching works in the value namespace only.

Also,

while special bindings for /namespaces/ can be trivially implemented with a

hash table, the lexical binding is not

--- it's worth a library. This is what this library is for.

[1] Like =(cons A B)= matching clause vs =(cons A B)= constructor.

• Namespaces in CL?

By /namespace/ I don't mean a /package/, which is a way to manage symbols. It is orthogonal to /namespace/.

CL already has major 2 namespaces, /function/ namespace and /value/ namespace (or /variable/ namespace), but there are actually more --- e.g., /class/ namespace. Since the same symbol can represent different objects in each namespace, this is obviously orthogonal to /package/. For example, all these below can coexist in a same file without errors, and each object is accessible with the corresponding function.

#+BEGIN_SRC lisp (in-package :cl-user)

(defclass foo () ()) (defun foo () nil) (defvar foo 1)

(find-class 'foo) ; -> #<STANDARD-CLASS FOO> (symbol-function 'foo) ; -> #<FUNCTION FOO> (symbol-value 'foo) ; -> 1

(make-instance 'bar) ; -> SIMPLE-ERROR (symbol-function 'bar) ; -> UNDEFINED-FUNCTION (symbol-value 'bar) ; -> UNBOUND-VARIABLE #+END_SRC

| namespace | accessor | unbound condition | boundp | binding | |-----------+-----------------+--------------------+---------+-------------| | class | find-class | SIMPLE-ERROR | n/a | n/a | | function | symbol-function | UNDEFINED-FUNCTION | fboundp | flet,labels | | value | symbol-value | UNBOUND-VARIABLE | boundp | let |

/Some/ namespaces in CL can be said to overlap with each other. For example:

• class namespace --- with type, condition and struct namespace
• function namspace --- with macro-function and generic-function namespace
• value namespace --- with symbol-macro namespace.

** Macro DEFINE-NAMESPACE

: (define-namespace name &optional (expected-type t) (binding t) (documentation ""))

This macro defines a namespace. For the given name of namespace X, DEFINE-NAMESPACE defines 4 functions/macros:

• =#'symbol-x, #'(setf symbol-x)= : accessor to the global binding. Optionally, =expected-type= provides =ftype= proclamation and results in the better optimization. =expected-type= is not evaluated.
• =#'x-boundp= : unary function returning a boolean
• condition =UNBOUND-X= which is signaled when trying to access the value of an unbounded symbol.
• macro =(X-LET (binding...) body)= : lexical binding. Can be turned off when =binding= is nil.

** Extending the usability of =documentation= and =describe=

=define-namespace= also defines a method for =cl:documentation= and extend =cl:describe-object=. For example, you will be able to =(setf (documentation 'mysymbol 'x) "description")= and you will see it pretty printed in =(describe 'mysymbol)=.

Here is an example used in TRIVIA pattern matcher. Trivia has an =assoc= pattern, and everyone would feel happy if we can browse the documentation of this pattern from SLIME C-c C-d. Below is such an output on SBCL.

While such a practice is taken by some libraries (e.g. QL-HTTP and Stefil defines =describe= methods), those facility is made independently, and this feature is not much popular.

#+begin_src diff COMMON-LISP:ASSOC [symbol]

ASSOC names a compiled function: Lambda-list: (ITEM ALIST &KEY KEY (TEST NIL TESTP) (TEST-NOT NIL NOTP)) Declared type: (FUNCTION (T LIST &KEY (:KEY (OR FUNCTION SYMBOL)) (:TEST (OR FUNCTION SYMBOL)) (:TEST-NOT (OR FUNCTION SYMBOL))) (VALUES LIST &OPTIONAL)) Documentation: Return the cons in ALIST whose car is equal (by a given test or EQL) to the ITEM. Known attributes: call, foldable, flushable, unsafely-flushable Source file: SYS:SRC;CODE;LIST.LISP

+Symbol ASSOC is bound in a namespace PATTERN:

• Value: #<FUNCTION 'ASSOC {1004B19A0B}>
• Documentation:
• It matches when the object X is a list, and then further matches the contents
• returned by (cdr (assoc item X...)) against SUBPATTERN.
• If :KEY and :TEST is specified, they are passed to ASSOC. #+end_src

Note that /namespace/ itself has its own namespace. The optional argument =documentation= to =define-namespace= is a docstring of the namespace itself. It will be set to =(setf (documentation NAME 'namespace) documentation)= and will also be visible from =describe=.

Examples are in [[EXAMPLE.org]] .

• Expected Usecase?

Every time you want to define a =define-cool-object= macro. E.g.,

• in [[https://github.com/guicho271828/eazy-project][eazy-project]], [[https://github.com/guicho271828/eazy-project/blob/master/src/defmenu.lisp#L24][defmenu]]
• in [[https://github.com/AccelerationNet/function-cache][function-cache]], [[https://github.com/AccelerationNet/function-cache/blob/master/src/cache.lisp#L4][defcached]] (currently implemented with hash tables)
• in [[https://github.com/m2ym/optima][optima]], [[https://github.com/m2ym/optima/blob/master/src/pattern.lisp#L337][defpattern and pattern-expand-function]] (currently implemented with symbol properties)
• in [[https://github.com/Bike/compiler-macro][compiler-macro]], [[https://github.com/Bike/compiler-macro/blob/master/hint.lisp#L10][define-compiler-hinter]] (currently implemented with hash tables)
• in [[https://github.com/cffi/cffi][cffi]], [[https://github.com/cffi/cffi/blob/master/src/libraries.lisp#L129][define-foreign-library]] (currently implemented with hash tables)

• Other misc

** Macro NAMESPACE-LET / NSLET

=LET= with ability to lexically bind any value in the namespace. It currently supports /function, labels, value, symbol-macro, macrolet, restart, handler/ [2] namespaces and the user-defined namespaces.

Full examples are in [[EXAMPLE.org]] .

#+BEGIN_SRC lisp (namespace-let ((#'x (y) (1+ y)) ((macro x) (y) (1+ y)) ((macro y) (y) (1+ y)) (#'x (y) (1+ y)) ((label y) (y) (y y)) ((symbol-macro sm) 0) (b 0)) (let ((b 1)) (print :x)))

;; (PROGN ;; (FLET ((X (Y) (1+ Y))) ;; (MACROLET ((X (Y) (1+ Y)) ;; (Y (Y) (1+ Y))) ; same kinds of bindings are merged ;; (FLET ((X (Y) (1+ Y))) ;; (LABELS ((Y (Y) (Y Y))) ;; (SYMBOL-MACROLET ((SM 0)) ;; (LET ((B 0)) ;; (PROGN ;; (LET ((B 1)) ;; (PRINT :X)))))))))) #+END_SRC

[2] restarts and handlers have the dynamic scope only.

** Package LISP-NAMESPACE

it has =(:nicknames lispn)= .

• Design?

I'm wondering which abbreviation to =namespace-let= is appropriate. It should be something consistent with the historic name as =let=. However, I do not like names like =let+= because they are not self-expressive --- =let+= does not describe how it's different from the original =let=. =bind= and =where= are not considered good either, due to the similar reason.

I adopted =nslet=, thanks to masatoi0@twitter's advice. However, there is another alternative: Make it =let= and force the user to shadow =cl:let=? (nah I don't like it.) I'm still searching for a crazy bright idea.

Here are the remaining TODOs:

• X-let does not recognize =(declare (special ...))= currently.

• Dependencies

This library is at least tested on implementation listed below:

• SBCL 1.2.8 on X86 Linux 3.13.0-44-generic (author's environment)
• CCL 1.10-r16196 (LinuxX8664)

Also, it depends on the following libraries:

• alexandria by ** : Alexandria is a collection of portable public domain utilities.

• Author & Copyright

Copyright (c) 2015 Masataro Asai ([email protected])

Licensed under the LLGPL License.