[Haskell-cafe] Why Haskell?

Simon Peyton-Jones simonpj at microsoft.com
Mon Jul 24 04:31:20 EDT 2006

| I think I understand my issue now with this (other than the anomaly of
| the above example).  I've been using the make option with ghc to
| all the dependent sources, creating binaries for all of them.  Those
| binaries can be loaded into GHCi, but if you do so it will not make
| imports available to you for use.  Thus my main.hs has the header
| import Matrix
| import Parsefile
| import Array
| import NetPrams
| import System.IO.Unsafe
| .....
| If main.hs has not been brought up to date, I can load main.hs into
| interpreter and the functions defined in Matrix for example will be in
| scope and usable.  If on the other hand I've just run ghc on main, I
| load main.hs in, but the functions in Matrix will not be available.
| Perhaps the solution is to create a script file that loads all the
| modules in and adds them to the current scope.

The GHC user manual discusses this point:


When you *compile* a module, GHC does a whole lot of inlining, and
functions that are exported may not even exist any more.  That's why you
can't necessarily see the full top-level scope of a compiled module (the
:m *M form described in the manual).  If you *interpret* a module, GHC
is careful never to discard any top-level definition, so that you can
see the full top-level scope, just as you wrote it.

Maybe there should be a way to tell GHC to retain top level defns even
when compiling; but currently the story is that you must interpret the
.hs files if you want to see the top level defns.  


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