*To*: Brian Huffman <brianh at cs.pdx.edu>*Subject*: Re: [isabelle] argument order of List.foldr*From*: Alexander Krauss <krauss at in.tum.de>*Date*: Sat, 06 Mar 2010 21:28:06 +0100*Cc*: isabelle-users <isabelle-users at cl.cam.ac.uk>*In-reply-to*: <cc2478ab1003061009r64142752u7d2d64a7d128953c@mail.gmail.com>*References*: <cc2478ab1003061009r64142752u7d2d64a7d128953c@mail.gmail.com>*User-agent*: Mozilla-Thunderbird 2.0.0.22 (X11/20091109)

Hi Brian,

Alex Brian Huffman wrote:

Here is the type of List.foldr from the Standard ML basis library: val foldr : ('a * 'b -> 'b) -> 'b -> 'a list -> 'b and the type of foldr from Haskell's List library: foldr :: (a -> b -> b) -> b -> [a] -> b But List.foldr in Isabelle has this type: foldr :: "('a => 'b => 'b) => 'a list => 'b => 'b" Why are the arguments in that order? The standard argument order would be much more useful for partial application. Maybe it is based on Isabelle's Library.foldr, which has this type: Library.foldr : ('a * 'b -> 'b) -> 'a list * 'b -> 'b Since it has an uncurried type, the argument order doesn't make any difference here as far as partial application is concerned, and I recognize that there is a mnemonic benefit to this argument order: Library.foldr (op +) ([1,2,3], 4) = 1 + (2 + (3 + 4)) But I think that being amenable to partial application is more important. Does anyone else have an opinion on this? - Brian

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