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Add a TR Guide section about ->* and optional args

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This commit is contained in:
Asumu Takikawa 2014-02-14 17:24:23 -05:00
parent 1c5f6714a8
commit a9b09f2910
1 changed files with 30 additions and 0 deletions
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pkgs/typed-racket-pkgs/typed-racket-doc/typed-racket/scribblings/guide/types.scrbl
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@ -71,6 +71,36 @@ each of these types.
(lambda: ([c : Char]) (values (string c) (char->integer c)))]
@section{Types for Functions with Optional or Keyword Arguments}
Racket functions often take optional or keyword arguments in addition
to standard mandatory arguments. Types for these functions can written
concisely using the @racket[->*] type constructor. Here are some
examples:
@racketblock[
(->* () (Number) Number)
(->* (String String) Boolean)
(->* (#:x Number) (#:y Number) (values Number Number))
]
The first type describes a function that has no mandatory arguments,
one optional argument with type @racket[Number], and returns a
@racket[Number].
The second requires two mandatory arguments, no optional arguments,
and produces a @racket[Boolean]. This function type could have been
written using @racket[->] as @racket[(-> String String Boolean)].
The third requires a mandatory keyword argument with the keyword
@racket[#:x] and accepts an optional argument with keyword @racket[#:y].
The result is two values of type @racket[Number].
@;; FIXME: examples for these are not great right now because
@;; the lambda: does not allow optional arguments and lambda does
@;; not allow type annotations. This will be fixed in the future,
@;; so update the Guide then.
@section{Union Types}
Sometimes a value can be one of several types. To specify this, we