crew

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• CREW the command line rewriter Crew is a tool to rewrite commands on the fly depending on the current directory or project. Basic use cases are :

• selecting the correct version of a tool , ex =ghc-7.8.4= or =ghc-7.10.3=
• integrating =cabal new-build= with current editor plugin.
• using =stack= for tool designed to use =cabal=
• etc ...

Crew allows to change the executable, modify or even drop arguments, and set environment variables. Crew is written in Haskell and has been designed to solve some problems specific to Haskell tooling (mainly cabal new-build and ghc-mod), can be used to anything which needs a aliasing per directory.

However, it is at the moment still experimental and I'm taking any responsibilities if anything happen using it. Crew has been designed for Linux. It should compile on Windows, but I don't know if it is usable or not.

• How it works When Crew is executed, it tries locate a =.crew= file an located in the current directory or above. It applies then the transformation corresponding to the name it's been invocated with (.i.e =argv[0]=).

** Setup In order to execute Crew instead of the command to rewritten, the trick is to create of copy of Crew with the name of the command to rewrite. Of course, this new command needs to be in the PATH in a directory with a higher priority.

I recommend to create a =.crew-bin= directory in your home directory and setup your path to use it first. Add =PATH=~/.crew-bin:$PATH= at the end of your usual rc. However to make it work with program launched from the desktop, you might need to add in your =.profile= as well.

Let's say you want to tweak =cabal= to call =new-build= whenever =build= is called. You'll need to link crew as cabal in your=.crew-bin= directory. If you have installed crew using =cabal= it should be in =~/.cabal/bin=. So you'll need =cd .crew-bin; ln -s ~/.cabal/bin/crew cabal=.

Now, you'll need to tell were the real =cabal= is, otherwise Crew will just loop, trying to call =cabal= but only finding itself. For this, create a =.crew= in your home directory with the following :

#+BEGIN_SRC yaml cabal: cmd: /home//.cabal/bin/cabal #+END_SRC

Alternatively you can alter the path to find the real cabal. You don't need them to specify the command. Crew will use the orginal command.

#+BEGIN_SRC yaml cabal: path: prepend: "/home/:" #+END_SRC

Note at the moment, path needs to be absolute (and shell expansion like =~= doesn't work yet). To check that you are calling crewed and not the original cabal, you can add a message in the configuration file

#+BEGIN_SRC yaml cabal: cmd: /home//.cabal/bin/cabal msg: This is a crewed version of cabal #+END_SRC

Any invocation of =cabal= should display =This a crewed version of cabal= before any real cabal messages.

Now, we want to replace =cabal build= with =cabal new-build= but only for the =test-newbuild= project. Create a new =.crew= file in the =test-newbuild= directory with the following

#+BEGIN_SRC yaml cabal: msg: CREW: build => new-build sub: build: new-build #+END_SRC

=sub= if for subcommand. It only replace =build= by =new-build= if build is the first argument of cabal. We don't need to specify the =cmd=. They will be inherited from the =~/.crew=.

If you type =cabal build=, you should see the =CREW: build => new-build= (or new message and the result new-build). That's not really exciting, you could have typed =cabal new-build= yourself, but it's handy if you use a text editor with some shortcut bound to call =cabal build=. For example, I use Spacemacs, and pressing =<SPC> c c= will now result in a new-build.

I have other projects using stack. I can configure Crew to call =stack build= when Spacemacs try to call =cabal build= (see examples).

** Configuration file The configuration file is a simple YAML file, which each entry corresponding to a command and different sections. *** Command =cmd= specifies the command to execute. *** Subcommand =sub= specifies a list of mapping for subcommands, i.e. the first argument of a command. =sub= can be either a value, or a mappings. A mapping allows to specify a different set of arguments mappings, environment variables and message for each subcommand. Use =smdcmd= to specify a different sub-command within a mapping.

The following example redirect =cabal build= to =cabal new-build= #+BEGIN_SRC yaml cabal: sub: build: new-build #+END_SRC

We can add a message specify to the build command, this way :

#+BEGIN_SRC yaml cabal: cmd: stack sub: build: subcmd: new-build msg: "Cabal new-build" #+END_SRC

Note, the need to add =subcmd: new-build=, to specify the sub-command mapping. *** Arguments =args= specifies a list of mapping for all arguments. At the moment only long argument of flag are replaced. Can be specified at a command or sub-command level. *** Skiping arguments An argument can be skipped by replacing with an empty string. *** Message =msg= specifies a message to display before executing the command. Can be specified at a command or sub-command level. *** Setting environment variables =env= specifies a list of environment variables to set or modify. Variable can be either set with a new value or modified by prepending and/or appending a value to the existing value. Examples;

#+BEGIN_SRC yaml PATH: /home/user/.local/bin #+END_SRC Set =PATH= to =/home/user/.local/bin=

#+BEGIN_SRC yaml PATH: prepend: "/home/user/.local/bin:" append: :/home/user/.other/bin #+END_SRC

set is equivalent to =/home/user/.local/bin:$PATH:/home/user.other/bin=. Note the =prepend= value needs to be between quote. This is due to yaml not liking value ending with =:=.

At the moment, environment variable in the value are not expended. Can be specified at a command or sub-command level. *** Inheritence All files name =.crew= in or above the current directory are loaded with children version overriding parent one. For example, in our example above, =cmd= is defined in =~/.crew= but =msg= is defined in =~/.crew= AND =~/test-newbuild/.crew=. =cmd= will be inherited from =~/.crew= but =msg= will use =msg= from =~/test-newbuild= *** Reading environment variables Values can be overridden with environment variable using the =_env:VAR:default= syntax (taken from =Yesod=). Example :

#+BEGIN_SRC yaml cabal: msg: _env:CABAL_MESSAGE: CREW: build => new-build #+END_SRC

Typing =cabal= will result in

#+BEGIN_SRC shell

cabal CREW: build => new build cabal: no command given (try --help) #+END_SRC

But if CABAL_MESSAGE is set if will be used instead of the default message.

#+BEGIN_SRC shell

CABAL_MESSAGE="env message" cabal env message cabal: no command given (try --help) #+END_SRC

• Examples ** cabal new-build Cabal-1.24 introduce a NIX-style build. This is a great feature but it requires some new commands instead. We can use crew to map the old command to the new ne.

#+BEGIN_SRC yaml cabal: cmd: /cabal sub: build: new-build configure: new-configure repl: new-repl old-build: build old-configure: configure old-repl: repl #+END_SRC

In case you need, the old commands, they are mapped as =old-=.

** redirect cabal build in Spacemacs to use stack Another use of Crew is to redirect =<SPC> c c= in Spacemacs to stack. This can be achieved with the following Here we don't need to map the sub-command are they are both called build. However, the argument to pass some options to GHC has a different name, so we remap it.

#+BEGIN_SRC yaml cabal: cmd: /stack args: --ghc-option: --ghc-options #+END_SRC

** Add watch command to stack The =stack build --file-watch --fast= automatically builds your project on change. We can alias it to =stack watch= :

#+BEGIN_SRC yaml stack: watch: build --file-watch --fast #+END_SRC ** ghc-mod =ghc-mod= needs to be compiled with the same version of GHC than the code your use =ghc-mod= for. This is a problem when working with projects using a different version of GHC, as you can only have one version of ghc-mod installed globally at the same time. A solution to this problem is to rename ghc-mod with it's version number and use crew to select the appropriate version depending on the project.

In a directory using GHC-7.8.4

#+BEGIN_SRC yaml ghc-mod: cmd: ghc-mod-7.8.4 #+END_SRC

In a directory using GHC-7.10.3 #+BEGIN_SRC yaml ghc-mod: cmd: ghc-mod-7.10.3 #+END_SRC

• Todo This a work in progress, pull requests are welcomes !

** TODO add global configuration ** TODO expand home variable ** DONE allows multiple arguments expansion ** DONE prepend append value to env variable CLOSED: [2016-09-14 Wed 21:51] allow things similar PATH = newpath:$PATH ** TODO add log options ** TODO display message to sderr ** TODO add section example -mpatter => --test-arguments -mpatter ** TODO crew command to generate links and default config ** TODO options to bypass crew execute command by removing =.crew-bin= from the path

** TODO use regexp