cenv

Chicken 5 virtual environments.

Description

A single csi script, cenv.scm, which creates a self-contained Chicken 5 environment in a specified directory. It remembers which Chicken you used to create it, and it keeps its own repository of eggs, which extends that base Chicken.

When the environment is active, csi and csc and compiled programs use this repository, falling back to the base repository if an extension does not exist. chicken-install installs eggs into this new repository. chicken-uninstall is limited to the new repository, and chicken-status shows both. Generally, everything behaves as you expect.

cenv could be useful if:

• You are a regular user using the system Chicken and you have no permissions to, or don't want to, install eggs systemwide.
• You want to test or switch between different versions of eggs, without creating an entire Chicken installation to house them.

Usage

Initialize an environment by running cenv.scm with csi, using the init verb. The full path of the Chicken you use is permanently stored in the new environment (even if you don't call it with a full path).

csi -s /path/to/cenv.scm init <directory>
~/mychicken/csi -s /path/to/cenv.scm init <directory>
/path/to/cenv.scm init <directory>

Enter the environment by sourcing center (from bash), then running commands.

source myenv/bin/center
chicken-install ...

With cexec you can run a one-off command in the environment. It will use /bin/sh, so you can run it from a weird shell, such as fish.

./myenv/bin/cexec chicken-install ...

At the moment, there is no cexit to leave a centered environment. You should start a subshell first if you need the ability to exit, or use cexec.

Example -- installing an egg

Nothing up my sleeve, base64 is not installed:

$ csi -R base64 -p '(base64-encode "hello")'
Error: (import) during expansion of (import ...) - cannot import
from undefined module: base64

Init environment in ~/tmp/myenv:

$ cd ~/tmp
$ csi -s ~/scheme/cenv/cenv.scm init myenv
Using CHICKEN 5.0.0 in /Users/jim/local/chicken/5.0.0
Initializing repository in myenv
New repository path:
(/Users/jim/tmp/myenv/lib /Users/jim/local/chicken/5.0.0/lib/chicken/9)

Enter the new environment, and install base64:

$ bash                       # Start a subshell
$ source myenv/bin/center
$ chicken-install base64
building srfi-14
  installing srfi-14
building srfi-13
  installing srfi-14
building base64
  installing base64

$ tree myenv/lib
myenv/lib
├── base64.egg-info
├── base64.import.so*
├── base64.link
├── base64.o
├── base64.so*
├── srfi-13.egg-info
├── srfi-13.import.so*
├── srfi-13.link
├── srfi-13.o
├── srfi-13.so*
├── srfi-13.types
├── srfi-14.egg-info
├── srfi-14.import.so*
├── srfi-14.link
├── srfi-14.o
├── srfi-14.so*
└── srfi-14.types

Run base64 (still in the new environment):

$ csi -R base64 -p '(base64-encode "hello")'
aGVsbG8=

Exit the environment (subshell); base64 no longer works:

$ exit
$ csi -R base64 -p '(base64-encode "hello")'
Error: (import) during expansion of (import ...) - cannot import
from undefined module: base64

Note that the base64 dependencies srfi-13 and srfi-14 were installed in your repository as well. If you had them installed in your base Chicken, they would not be installed unless chicken-install deemed it necessary, for example to satisfy a version requirement.

Example -- two Chickens

Initialize 2 environments, using 2 different versions of Chicken 5. cexec and center use the Chicken you initialized the environment with.

$ ~/local/chicken/5.0.0/bin/csi -s ~/scheme/cenv/cenv.scm init c500
Using CHICKEN 5.0.0 in /Users/jim/local/chicken/5.0.0
Initializing repository in c500
New repository path:
(/Users/jim/tmp/c500/lib /Users/jim/local/chicken/5.0.0/lib/chicken/9)

$ ~/local/chicken/5.0.1/bin/csi -s ~/scheme/cenv/cenv.scm init c501
Using CHICKEN 5.0.1 in /Users/jim/local/chicken/5.0.1
Initializing repository in c501
New repository path:
(/Users/jim/tmp/c501/lib /Users/jim/local/chicken/5.0.1/lib/chicken/10)

Run each version of chicken-install using cexec and check its version.

$ ./c500/bin/cexec chicken-install -version
5.0.0

$ ./c501/bin/cexec chicken-install -version
5.0.1

Alternatively you could use center:

$ chicken-install -version          # default chicken in my PATH
4.12.0

$ source c501/bin/center
$ chicken-install -version
5.0.1

Technical

Behind the scenes, cenv is just manipulating the environment variables CHICKEN_INSTALL_PREFIX, CHICKEN_INSTALL_REPOSITORY, CHICKEN_REPOSITORY_PATH and PATH.

Caveats and TODOs

• cenv extends the base Chicken's environment; the new environment is not completely isolated.
• It would be possible to isolate the environment more by copying only a list of known base modules from the base repository into the new repository at initialization time, and omitting the base repository from the repo path.
• Egg shared data may not be found inside a cenv, as (lacking support from the core) every egg hacks together a method of locating its shared data. Special action is taken in center to set the chicken-doc repository location correctly. If we turned cenv into a library, eggs could use it to standardize finding this data, and we could eliminate special casing.