Template Haskell and the command line

[Simon Marlow]

> Template Haskell is frightfully good and we want to get rid of cpp and
> use it instead, but there's one tiny problem, namely that for cpp it
> is possible to define variables on the command line 
> (-DSIMON=MARLOW and so
> on) while with Template Haskell it doesn't seem to be.  Could there be
> some kind of dictionary, like the cpp environment variables, which the
> Template Haskell code has access to?
> 
> One obvious way would be to accept the -D/-U arguments, and 
> provide Haskell
> functions which look at them.
> 
> Of course one /could/ presumably use System.getArgs and 
> analyse the arguments
> to ghc oneself, but that would mean making guesses about the 
> current GHC syntax.
> 
> In the meantime we shall still replace cpp with Template 
> Haskell, but find
> another way.  Thanks for Template Haskell!

What's wrong with using environment variables, with
System.Envorinment.getEnv?  To use your example, you would write:

   $ SIMON=MARLOW foo

Cheers,
	Simon