[Haskell-cafe] Comments from OCaml Hacker Brian Hurt

Jonathan Cast jonathanccast at fastmail.fm
Thu Jan 15 18:33:54 EST 2009

On Thu, 2009-01-15 at 15:25 -0800, Max Rabkin wrote:
> On Thu, Jan 15, 2009 at 3:16 PM, Cale Gibbard <cgibbard at gmail.com> wrote:
> > However, "Appendable" carries baggage with it which is highly
> > misleading. Consider, for instance, the monoid of rational numbers
> > under multiplication (which, by the way, is quite useful with the
> > writer transformed list monad for dealing with probabilities) -- you
> > can claim that multiplication here is a sort of "appending", perhaps,
> > but it's not really appropriate.
> It's rather funny that there's a mathematical sense in which all
> monoid operations *are* appending. The free monoid on a set has
> appending as its operation, and the free monoid is initial in the
> category of monoids on that set (by definition), so all monoid
> operations are appending, modulo some equivalence relation.

Right.  So we start explaining that to new Haskellers.  We already have
participants in this discussion who can never quite remember where the
term Monad comes from; and now we need them to remember some complicated
argument about quotients of free monoids justifying the term `Append'?


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