Generic Lisp: How to get (in a package ...) to work from Emacs Slime

Question

64-bit version of Windows 7
Clozure Common Lisp Version 1.9 WindowsX8632
Emacs 24.3.1
Slime Change Date 2014-06-17

I have an example .lisp file that starts as follows:

(ql:quickload 'qt) (in-package "QT") 

The rest of the program displays a dialog box. When I run this from the command line, wx86cl -load helloqt.lisp seems to work fine. When I run this from Emacs Slime ( Cx Ck ), it says that there is no "QT" package. However, if I first evaluate the first line individually ( Cx Ce ), then I can compile all this and work, modulo common problems with trying to start a QT stream from Slime on Windows.

How to do this so that I can compile / run the file from emacs without having to manually evaluate the first line first?

Also, why (in-package ...) doesn't change the current package in a Slime session? I have to change it manually if I want to interact with the contents of the package.

Answer 1

When you compile a file as a whole, it is first read as a whole. At that time, none of them has been rated yet, so the QT package is not yet defined.

You can use eval-when to evaluate something at an earlier time or use the system definition tool (ASDF is predominant today) to boot your system in the correct order.

eval-when :

 (eval-when (:compile-toplevel :load-toplevel :execute) (ql:quickload '#:qt)) (in-package #:qt) 

Please note that you usually should not extinguish in library packages, but define your own fresh package to store your code:

 (eval-when (:compile-toplevel :load-toplevel :execute) (ql:quickload '#:qt)) (defpackage #:qt-example (:use #:qt)) (in-package #:qt-example) ;; your code here 

(If you're interested, defpackage , defun , defclass , etc. are specially designed macros that expand to form inside eval-when .)

This is sometimes normal for small one-time scripts. For systems of any remarkable size, especially if they have multiple source files, use ASDF:

 ;;;; qt-example.asd (in-package #:cl-user) (asdf:defsystem #:qt-experiments :description "Some experiments with QT." :serial t :components ((:file "package") (:file "qt-example")) :depends-on (#:qt)) ;;;; package.lisp (defpackage #:qt-example (:use #:qt)) ;;;; qt-example.lisp (in-package #:qt-example) 

ASDF comes with most open-source Common Lisp implementations. You may need to configure the ASDF registry. I like to have one or two base directories for all my local projects, so I can just put the following in ~/.config/common-lisp/source-registry.conf :

 (:source-registry (:tree (:home "devel")) (:tree (:home "src")) :inherit-configuration) 

ASDF then finds all the systems defined below these directories. In SLIME, you can simply use ,load-system or ,open-system from REPL with the system name to load it, respectively. open all the files in it, optionally download it.

When compiling one top-level form (using Cc Cc ) from a file, SLIME looks back from there for the in-package form to find out which package it should accept. Usually you should have only one in-package form for each file at the top.

A commonly used shortcut is Cc ~ in Lisp source files, which switches the REPL to the file directory and the effective package at a point.