[Haskell-cafe] Generating Code

[Iustin Pop]

On Fri, Dec 09, 2011 at 10:30:18PM +0100, L Corbijn wrote:
> The major set of problems for using template haskell is that it
> doesn't have the correct features, or better said it tries to solve
> another problem. Template haskell generates code into an existing
> module, while for this problem there is no module yet to generate it
> into. Of course I could generate those modules and let template
> haskell make the FFI imports, but then the problem remains how to
> generate those modules. So template haskell seems (as I see it) to
> solve the problem of writing almost the same code twice by generating
> it from some parameters coded in some source file. Another problem is
> that the export and import lists of the modules need to be generated
> too and this seems not an option for TH.

On Fri, Dec 09, 2011 at 04:27:31PM -0600, Antoine Latter wrote:
> For my case, template haskell can't create modules, and template
> haskell solves a different problem - I've not interested in creating
> Haskell declarations from Haskell declarations - I'm interested in
> creating Haskell modules from an external, formal,  specification. In
> a sense I'm compiling to Haskell.

This answer is for both the above quotes. While TH is not perfect (and
sometimes tedious/difficult to write in), it's not restricted to simply
generate code based on some parameters in an existing Haskell file.

It cannot generate modules, true, but other than that you could have a
module simply like this:

  module Foo where

  import …

  $(myBuilder)

Where myBuilder doesn't take any parameters, just reads some external
(XML, text file, whatever) and build the code from scratch.

I might misunderstand the problem, but I think that you _could_ use TH
for "compiling" to Haskell, as long as you have a Haskell parser for the
external/formal spec.

regards,
iustin