[Haskell-cafe] singleton types

Don Stewart dons at galois.com
Sun Apr 25 17:25:02 EDT 2010

> 2010/4/25 Günther Schmidt <gue.schmidt at web.de>:
> > Hello,
> >
> > HaskellDB makes extensive use of Singleton Types, both in its original
> > version and the more recent one where it's using HList instead of the legacy
> > implementation.
> >
> > I wonder if it is possible, not considering feasibility for the moment, to
> > implement HaskellDB *without* using Singleton Types.
> Would you please define "singleton type"?

Funny, we had a discussion about this at work this week (in the context
of adding singleton types to Cryptol to support some witness/proof

A nice defn is Oleg's:


    "we define particular types such that the corresponding sets of values
    consist of only one value, the conceptual barrier between elements and
    sets of elements disappears"

Which is the intuitive notion, I think.

-- Don

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