[Haskell-cafe] Re: existential types

Simeon Mattes simeon.mattes at gmail.com
Wed Feb 13 12:24:27 EST 2008

The help of all was very useful. But since Jake gave me an example I prefer to
follow this up. 

Although I 'm not so familiar generally with datatypes I have understood you. It
seems in this example that with existential types we can put in the same list
different types although generally this is not allowed. I have tried to write
this example with the ghc compiler 6.8.2 but there was an error

pare error in data/newtype declaration.

I have also tried to find the etymology of the word existential, since some
times somebody can easily find a better answer, but I can't figure out why this
is so. (really why "existential" types?). Maybe a completed example would be
more helpful.

existence Look up existence at Dictionary.com c.1384, from O.Fr. existence, from
L.L. existentem "existent," prp. of L. existere "stand forth, appear," and, as a
secondary meaning, "exist;" from ex- "forth" + sistere "cause to stand" (see
assist). Existential as a term in logic is from 1819. Existentialism is 1941
from Ger. Existentialismus (1919), ult. from Dan. writer Søren Kierkegaard
(1813-55), who wrote (1846) of Existents-Forhold "condition of existence,"
existentielle Pathos, etc.

(I hope this way of questioning is not so strange)

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