I just pushed a generalization for the type of `curry'. As Carl said, TR's type system can't fully describe the behavior of `curry'. With its new type, `curry' works on n-ary functions, but the returned function is limited to accepting its arguments in two steps, the first one first, then all the others.
Vincent At Mon, 25 Feb 2013 13:21:23 -0500, Carl Eastlund wrote: > > [1 <multipart/alternative (7bit)>] > [1.1 <text/plain; UTF-8 (7bit)>] > The type of curry is correct, but imprecise. It does not express all > possible uses of curry. The curry function can be used to split any > function application into an arbitrary number of stages, each with an > arbitrary number of arguments. There is no way to write down that type. > Typed Racket needs to know how many stages there are to the function > application -- that's the nesting level of "->" -- and how many arguments > all but the last step take -- because there can be only one "..." in the > initial function type, and it must be at the end of the arguments. > > Right now the type is specialized to two stages, each with one argument. > It could be generalized a bit further -- perhaps to allow arbitrary > arguments at the second stage, or to allow two arguments at the first > stage, or to allow a three-stage case as well, or some combination > thereof. However, this specialization can only go to some arbitrary, > finite degree without changing the type system, and each addition will > complicate the type of curry used in error messages. > > For now, that means you will have to define f1a explicitly, or write a more > specific instantiation of curry for your uses. In the future, perhaps the > TR implementers can broaden the type of curry a bit. Types for this kind > of higher-order function are an area of open research for TR, so perhaps > things will get better in the future. > > Carl Eastlund > > > On Sun, Feb 24, 2013 at 5:59 PM, Norman Gray <nor...@astro.gla.ac.uk> wrote: > > > > > Greetings, > > > > Is the type of 'curry' correct? > > > > #lang typed/racket > > > > (: f2 (Boolean Integer Integer -> Integer)) > > (define (f2 add? i1 i2) > > (if add? > > (+ i1 i2) > > (- i1 i2))) > > > > (define f1a (curry f2 #t)) ; fails to typecheck > > > > (f2 #t 2 3) > > (f2 #f 2 1) > > ;(f1a 10 20) > > > > ===> > > > > Welcome to DrRacket, version 5.3.3 [3m]. > > Language: typed/racket; memory limit: 128 MB. > > . Type Checker: Polymorphic function curry could not be applied to > > arguments: > > Domains: (a b -> c) > > (a b -> c) a > > Arguments: (Boolean Integer Integer -> Integer) True > > in: (curry f2 #t) > > > > > > > It works fine when currying a two-argument function. > > > > All the best, > > > > Norman > > (I'll resist any vindaloo jokes) > > > > > > -- > > Norman Gray : http://nxg.me.uk > > SUPA School of Physics and Astronomy, University of Glasgow, UK > > > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > > > > > [1.2 <text/html; UTF-8 (quoted-printable)>] > > [2 <text/plain; us-ascii (7bit)>] > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
