

Theorems for Free (1989) [pdf] - catilac
http://ttic.uchicago.edu/~dreyer/course/papers/wadler.pdf

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DougMerritt
I presume your post attracted little attention because people either didn't
know what it was from the title, or for those who did, it's perhaps too
familiar.

So a small explanation: in the functional community it's a famous classic
paper; by Philip Wadler. Abstract:

"From the type of a polymorphic function we can derive a theorem that it
satisfies. Every function of the same type satisfies the same theorem. This
provides a free source of useful theorems, courtesy of Reynolds' abstraction
theorem for the polymorphic lambda calculus."

It "gave rise to much research on functional language optimization"
[http://en.wikipedia.org/wiki/Philip_Wadler](http://en.wikipedia.org/wiki/Philip_Wadler)

See also
[http://en.wikipedia.org/wiki/Parametricity](http://en.wikipedia.org/wiki/Parametricity)

