On Mon, Jun 13, 2011 at 4:45 PM, M.C.A. (Marco) Devillers
<marco.devillers@gmail.com> wrote:
The urge to do I/O at all the wrong places is a born instinct.
The original poster was well aware how to factor out IO out of his program, as made apparent by his initial comment: "An option I suppose would be to read the dictionary at the top level, and then pass it all the way down to the analysis routine that uses it, but that exposes the details of how the analysis is done, and couples the top and bottom levels of the previously modular functions."
His original argument was a genuine observation that IO sometimes seems to be adverse to the loose coupling of modules. Dissing that argument away as: "you are doing IO at the wrong place," doesn't convince me the least.
There are ways to decouple IO from pure code. I often have a "Main" datatype which constructs a "pure context" (based on command line arguments, files and their contents, etc) which is then "interpreted" by pure code. In other words, this is a pure control structure, which is computed by IO (sometimes in an applicative style, sometimes in a monadic one), and then passed into the pure world for processing. This can be as tightly or loosely coupled as we like, assuming we understand that if a value is even partially based on the results of an IO computation, then IO is going to drive the computation of that value. There's no way around that.