Common-Lisp: defpackage vs in-package for context

[iicurtis]

When talking with the REPL, common-lisp needs to define a context to operate in. This is currently done by looking for the most recent (defpackage __context__). Does it make sense to instead look for (in-package __context__)? Or maybe either? (Not sure if that's possible with lua patterns)

[Olical]

We should be able to do that, yeah. It means adapting

conjure/fnl/conjure/client/common-lisp/swank.fnl

Line 15 in f50d4db

(def context-pattern "%(%s*defpackage%s+(.-)[%s){]")

The client API also supports a context function instead of a context-pattern string, so if we want to we could drop that pattern and export a function that checks for both, the context-pattern string is really just shorthand, it's more flexible than that.

So yeah, we could quite easily check for both in a particular order and make some decision about what the current context for the current document is. Maybe even base it on where in the file your cursor is right now for more contextual evals?

[Olical]

Pushed a change to develop noted in #561 and 20df0e0

Let me know what you think!

[russtoku]

I don't know much about Common Lisp but some research provided some help:

• In the How to load an existing project section of The Common Lisp Cookbook – Getting started with Common Lisp, it suggest that (in-package __context__) is what we should look for because forms evaluated after that should be in that package.

• In Chapter 20. Special Operators of Practical Common Lisp, Peter Seibel says:

  evaluating an IN-PACKAGE form changes the value of PACKAGE, which will affect the way subsequent forms are read.

• In the Appendix: Packages section of On Lisp by Paul Graham, he says:

  By calling in-package we can switch to a new package, creating it if necessary:

  > (in-package ’mine :use ’common-lisp) #<Package "MINE" 63390E>
  

  At this point there should be eerie music, because we are in a different world: foo here is not what it used to be.

I've also tried out https://github.com/monkoose/nvlime to see how the interaction with a Common Lisp REPL works. It does switch packages when it evaluates an in-package form. It also has a key mapping that lets you change the current package.