CODEWITHSUNDEEP
common-lisp
Flux
Flux

Reputation: 10930

When requiring modules, should the name be a string, symbol, or keyword?

What is the difference between the following?

(require "asdf")  ; String.
(require 'asdf)   ; Symbol.
(require :asdf)   ; Keyword.

Which should I use when requiring modules?

Upvotes: 3

Views: 131

Answers (2)

Flux
Flux

Reputation: 10930

This answer is specific to ASDF.

The recommended way to load ASDF is by using (require "asdf") (i.e. using a lowercase string). According to the ASDF manual, section 3 ("Loading ASDF"):

The recommended way to load ASDF is via:

(require "asdf")

The footnote says:

NB: all implementations except GNU CLISP also accept (require "ASDF"), (require 'asdf) and (require :asdf). For portability’s sake, you should use (require "asdf").

Upvotes: 0

user5920214
user5920214

Reputation:

The argument of require is a string designator which is

a designator for a string; that is, an object that denotes a string and that is one of: a character (denoting a singleton string that has the character as its only element), a symbol (denoting the string that is its name), or a string (denoting itself).

So any of the above will work. However, require is defined to make comparisons between module names using string=, which means that case matters. So this means that (require 'asdf) is the same as (require :ASDF) is the same as (require "ASDF") but is not the same as (require "asdf"). (In fact, ASDF adds both "asdf" and "ASDF" to *modules* so both will work.)

Personally, I use keyword symbols, so (require :asdf), (provide :spotbat), which means *modules* always ends up with upper-case strings.

I find the decision to use string= to compare module names a bit annoying, but it is what it is now, and it is also compatible with various other conventions: package names, for instance, are case sensitive. And in theory it would allow, for instance, a case sensitive lowercase-preferred language to exist alongside CL in the same image ((find-package "cl") could be the package that exported all its symbols).

Upvotes: 7

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