Init.m considerations and good practices

Question

As I never found (or perhaps I never search for it enough) a good article about how to manage the init.m files, I ended up developing my own "standard", but I wonder how bad I did it.

For example, my usual init.m is stored in C:\Documents and Settings\All Users\Application Data\Mathematica\Kernel\init.m (Windows) and I edit it using a text editor.

As I don't want the definitions to go into the Global context, the content is something like:

(** User Mathematica initialization file **)
Begin["MyInitContext`"];

Cl:=Clear["Global`*"];
(* Other definitions in this Context *)

End[]; (* End Context *)
$ContextPath = Prepend[$ContextPath,"MyInitContext`"];

I don't load packages from the init.m, because I want strict control over what I load, so I only define here shortcuts to utility functions I use on a daily basis and some options.

So: Any references to good practices? Better ways to achieve this kind of behavior? Any caveats?

Answer 1

Firstly, I would strongly recommend against putting anything significant init.m, since this invariably results in old stuff being broken when you come back to it after a few years. Much better to put your customizations on the path so you can quickly load it at the head of each notebook: That way the context is explicitly stated and you can easily change versions without breaking old stuff.

My current setup is to start with Needs["Janus`"] where the Janus directory has a custom init.m file that loads every file in the directory into the context. This means I can add utility functions in each their own file like this one (clear_cache.m):

ClearCache::usage="ClearCache[f] unsets all numeric-only downvalues of f, \
  see http://stackoverflow.com/questions/5086749"     

Begin["`Private`"];
ClearCache[f_Symbol] := 
  DownValues[f] = DeleteCases[DownValues[f], _?(FreeQ[First[#], Pattern] &)]
End[]

Here is the file Janus/init.m. Note that it prints out the name of the loaded extensions, all in the spirit of keeping the context explicit without too much hassle.

Module[{packageName,packageFileName,fileNames},
  (* $Input is set to Foo.m when evaluating Foo/init.m *)
  If[$Input=="", Print["init.m cannot run interactively"];Abort[]];
  packageName=StringDrop[$Input,-2];
  packageFileName=FindFile[packageName<>"`"];
  If[packageFileName==$Failed, Print["Unable to find package "<>packageName];Abort[]];
  fileNames=Select[
    FileNames["*.m",{DirectoryName@packageFileName},1],
    FileBaseName[#]=!="init"&];
  Print["Loading extensions from "<>DirectoryName@packageFileName<>" to context "<>packageName<>"`:"];
  BeginPackage[packageName<>"`"];
  Do[Print["Loading "<>fn]; Get@fn, {fn,fileNames}];
  EndPackage[]]

Answer 2

My Kernel/init.m looks like this:

AppendTo[$Path, Environment["MMA_LIB"]]
Needs["WRUtil`"]

WRUtil contains all of my little utilities and performs other initialization that takes into account the platform and Mathematica version. MMA_LIB is an environment variable that points to a directory full of Mathematica packages. That directory is kept under version control and can be shared by multiple Mathematica instances. I like to keep init.m short so that moving into a new Mathematica installation is as simple as typing two lines that I have committed to memory -- it is surprising how often I seem to have to do this.