Add package name to symbol

Question

This is a general symbol question in a specific context. The question I think I need to answer is: given a parameter containing a symbol 'foo, how do I manipulate the package part of the symbol so that it is eql to 'package:foo?

The more specific context: There is a unit-testing package, fiveam, that stores test functions in a hash table (it.bese.fiveam::*tests) with keys like package::test-name that hash to an object containing the tests. To run a test, one normally passes to the run! function a symbol that is a hash key: (run! 'package::test-name. If I'm calling run! from the tests package in which I defined the tests, I can just C-x C-e on (run! 'test-name). When calling from the SLIME REPL, I have to do (tests::run! 'tests::test-name), which is a mild inconvenience.

I'd like to run tests from cl-user with (run! 'test-name) and omit the package name. I thought it would be simple to wrap run! and add the missing package to the symbol, but all my tries fail, I guess in part because CL-USER:test-name is a different thing from tests:test-name.

The hash table in question uses eql to test equality. In the tests package:

(eql 'tests::foo 'foo) => T

In CL-USER:

(eql 'tests::foo 'foo) => nil

Various functions can return symbols (e.g. intern, make-symbol or format-symbol) but none of them are eql to the keys in the hash table:

(eql (alexandria:format-symbol t "foo::bar") 'foo::bar) => nil
(eql (make-symbol "foo::bar") 'foo::bar) => nil

Taking this out of the SLIME/REPL/FIVEAM context to generalize where I think the problem is, I can't figure out how to take 'bar and turn it into 'foo:bar as a symbol. I can specify it manually as 'foo:bar, but I can't seem to get anything to eql 'foo:bar, given 'bar.

Note: I don't really care about typing the extra few letters for a package name. What I'm really trying to do here is improve my understanding of scoping and specifying symbols.

Thank you.

(find-symbol (symbol-name 'bar) :foo) will return the symbol named BAR in the package named FOO if such a symbol is interned there. — jkiiski

Dirk Dirk · Accepted Answer · 2018-08-31T18:24:23

First off, I assume, that you know, that you can switch to the test package in the SLIME REPL using the extended command in-package (i.e., at the REPL prompt, type a comma , followed by in-package, you will be prompted for a package name), and that switching packages like that is simply inconvenient for you.

One solution could be to introduce a little helper function in whatever package you are currently working in:

(defun run-test (name &optional (package 'test))
   (funcall (find-symbol #.(symbol-name 'run!) package)
            (find-symbol (symbol-name name) package)))

or simpler (and assuming, that the definition of run! came from the fiveam package via :use or :import into the test package)

(defun run-test (name &optional (package 'test))
   (it.bese.fiveam:run! (find-symbol (symbol-name name) package)))

which you can now call as

(run-test 'check-everything)

Note, that we use find-symbol here instead of intern, since we expect the symbols to exist in all cases. If you want the helper to be easily accessible everywhere, you can even do

(defun :run (name &optional (package 'test))
   (it.bese.fiveam:run! (find-symbol (symbol-name name) package)))

and now you can call it as

(:run 'check-everything)

in regardless of the current package. Note, that I would recommend this only for helpers intended to be used in the REPL. Clobbering a global namespace (like the keyword function namespace) like that looks a little fishy to me.

Just for good measure: none of the code given has been tested (or even passed through a REPL) so beware. Also, I heartily recommend reading the chapter on packages and symbols in the CLHS, which should be considered The Ultimate Source™ for these things.

Add package name to symbol

2 Answers