[Haskell-cafe] Monad explanation

Gregg Reynolds dev at mobileink.com
Thu Feb 5 11:08:05 EST 2009

On Wed, Feb 4, 2009 at 8:18 PM, Richard O'Keefe <ok at cs.otago.ac.nz> wrote:

> On 5 Feb 2009, at 10:20 am, Gregg Reynolds wrote:
>> That's a fairly common representation, seems to work for lots of people,
>> but it caused me no end of trouble.  Values are mathematical objects; how, I
>> asked myself, can they possibly /be/ programs that do IO (or actions, or
>> computations, or <your metaphor here>)?  It doesn't make sense, says I,
> without reference to the rest of your message, of course values can /be/
> programs.

Not "programs", but "programs that do IO".  The point of the idiom is that
there's an external side effect involved.  What sticks in my craw is that "a
mathematical value with a non-mathematical side effect" is, well,
non-mathematical and possibly nonsensical.  I know it works for some (most?)
people, but for me it lacks Geometry and Theology.

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