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Qualified identifiers (was: RE: What *I* thinks Haskell Needs.)



> For bigger things which
> you want to identify, you can either use qualified module identifiers, or
> Haskell's type classes which at least let you establish and codify a
> motivation for using the same name for distinct things (namely, that their
> types are equivalent under a particular relation).

BTW, since I mentioned it, let me get on my hobby horse and implore other
Haskell programmers to _please_ make more use of the qualified ID syntax!
Haskell has had this feature for quite some time now, but I hardly ever see
it used...

Especially in modules that import a lot of other modules, it's

* easier to _recognize_ an identifier if it's prefixed by a module ID rather
than look through all the imported modules, and

* easier to _modify_ a module if all you need to do to pull in a new value
is to use it, rather than scrolling up, and adding it to the list of
identifiers in something like "import M (...)".

This is standard practice in both SML and Ocaml. (In fact, I would rather
not have to declare things like "import qualified M" at all...)

If you have a long module name, declare an alias:

  import qualified LongModuleName as LMN

BTW, another advantage of this syntax is that identifiers within their own
defining module get shorter, and consequently it gets easier to read. For
example, don't define "addToFM"; define "addTo" and then do "import
FiniteMap as FM". Sometimes this means having to hide Prelude identifiers
and qualify them at use (as it would be with "lookupFM" in GHC's FiniteMap
module) but is that such a great price to pay...?

Please. Pretty please? Pretty please with sugar on top?

--FC

P.S. Except infix combinators. These are ugly when you qualify them.





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