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Fix TR reference discussion of filters

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Thanks to Anthony Carrico

original commit: 290cc2dd7e02a023c2ed4b13827b98d2025a99fe
This commit is contained in:
Asumu Takikawa 2014-09-12 16:53:45 -04:00
parent 0af045fcf3
commit d614c6eea0
1 changed files with 4 additions and 3 deletions
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7
pkgs/typed-racket-pkgs/typed-racket-doc/typed-racket/scribblings/reference/types.scrbl
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@ -613,9 +613,10 @@ functions and continuation mark functions.
@ex[string?]
The filter specifies that when @racket[(string? x)] evaluates to a true value, the
variable @racket[x] can be assumed to have type @racket[String]. Likewise, if the
expression evaluates to @racket[#f], the variable has type @racket[String].
The filter specifies that when @racket[(string? x)] evaluates to a true value for
a conditional branch, the variable @racket[x] in that branch can be assumed to have
type @racket[String]. Likewise, if the expression evaluates to @racket[#f] in a branch,
the variable @emph{does not} have type @racket[String].
In some cases, asymmetric type information is useful in filters. For example, the
@racket[filter] function's first argument is specified with only a positive filter: