[Haskell-cafe] Applicative Functor or Idiom?

David Sankel camior at gmail.com
Fri Nov 20 14:09:01 EST 2009

After reading several recent papers I came to the understanding that
there isn't consensus on the name of Applicative Functors. Several
prefer to call them idioms:

"'Idiom' was the name McBride originally chose, but he and Paterson
now favour the less evocative term `applicative functor'. We have a
slight preference for the former, not least because it lends itself
nicely to adjectival uses, as in `idiomatic traversal'"[1]

I also noticed use of the term Idiom in [2], [3], and [4].

I'm writing a set of classes that includes AF's and I'm trying to
decide whether to call the class Idiom. Anyone have more information
on this question?


[1] Gibbons, J. and Oliveira, B. c. 2009. The essence of the iterator
pattern. J. Funct. Program. 19, 3-4 (Jul. 2009), 377-402. DOI=
[2] RALF HINZE (2009). The Bird Tree. Journal of Functional
Programming, 19 , pp 491-508 doi:10.1017/S0956796809990116
[3] S. Lindley, P. Wadler, and J. Yallop. Idioms are oblivious, arrows
are meticulous, monads are promiscuous. In Proc. of MSFP, 2008.
[4] The Arrow Calculus, Sam Lindley, Philip Wadler, and Jeremy Yallop.
Tech report, 2008.

David Sankel
Sankel Software

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