On Oct 6, 7:00 pm, Rich Hickey <[EMAIL PROTECTED]> wrote:
> On Oct 6, 9:36 am, Stuart Halloway <[EMAIL PROTECTED]> wrote:
>
>
>
> > Yes, that's better. Glad you like the idea.
>
> > Does anybody not named Stuart also want to see this added to
> > Clojure? ;-)
>
> > Stuart
>
> > > On Oct 3, 3:13 pm, Stuart Halloway <[EMAIL PROTECTED]> wrote:
> > >> (defmacro ?.
> > >> "like .. but drops out on null object"
> > >> ([x form]
> > >> `(. ~x ~form))
> > >> ([x form & more]
> > >> `(if-let x# (. ~x ~form) (.? x# [EMAIL PROTECTED]))))
>
> > > Interesting -- I like it. It doesn't seem to be totally compatible
> > > with "..", though:
>
> > > user=> (?. System (getenv "SHELL") (startsWith "/bin") getClass
> > > getName)
> > > java.lang.Exception: Unable to resolve symbol: startsWith in this
> > > context (NO_SOURCE_FILE:62)
>
> > > Also, if-let could give the wrong result in the (admittedly unlikely)
> > > situation that one of the methods returns Boolean.FALSE.
> > > Here's another take:
>
> > > (defmacro ?..
> > > "like .. but stops and returns nil if any method returns nil"
> > > ([x form]
> > > `(.. ~x ~form))
> > > ([x form & more]
> > > `(let [x# (?. ~x ~form)]
> > > (if (nil? x#) nil
> > > (?. x# [EMAIL PROTECTED])))))
>
> > > user=> (?.. System (getenv "SHELL") (startsWith "/bin") getClass
> > > getName)
> > > "java.lang.Boolean"
> > > user=> (?.. System (getenv "FOO") (startsWith "/bin") getClass
> > > getName)
> > > nil
>
> I'm not opposed, but we'll need to find another name. Leading ? is a
> likely candidate for rule syntax, and trailing means predicate.
This construct will be very useful.
How about the name "maybe" or similar along the lines of Haskell
"Maybe"
http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Maybe.html
Parth
>
> .?.
>
> ?
>
> Rich
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