Re: special case in binding vector syntax for function definitions?
On Fri, Jan 25, 2013 at 5:38 PM, Alan Malloy wrote:
> In (let [[x :as y] [1 2]]), there is already an object to make y "point to":
> the vector [1 2]. in ((fn [x :as y]) 1 2), there is no such object.
There's no such object for y to be the tail of in ((fn [x & y] y) 1 2
3), either, but the remaining arguments get accumulated in y
regardless. They even get accumulated in a map in ((fn [& {:as m}] m)
:x 1 :y 2).
--
Ben Wolfson
"Human kind has used its intelligence to vary the flavour of drinks,
which may be sweet, aromatic, fermented or spirit-based. ... Family
and social life also offer numerous other occasions to consume drinks
for pleasure." [Larousse, "Drink" entry]
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Re: special case in binding vector syntax for function definitions?
In (let [[x :as y] [1 2]]), there is already an object to make y "point to": the vector [1 2]. in ((fn [x :as y]) 1 2), there is no such object. On Friday, January 25, 2013 2:18:39 PM UTC-8, Ben wrote: > > Both of these work: > > user> (let [[x & y] [1 2]] [x y]) > [1 (2)] > user> (let [[x :as y] [1 2]] [x y]) > [1 [1 2]] > > And this works: > > user> ((fn [x & y] [x y]) 1 2) > [1 (2)] > > But this gives an exception (unsupported binding form): > > user> ((fn [x :as y] [x y]) 1 2) > ; Evaluation aborted. > > I would have expected this to work and return [1 [1 2]], with y bound > to the whole vector implicitly passed to the function (just as it's > bound to the tail of the whole vector implicitly passed in the third > case). > > This seems to happen because (apparently) the internals of fn* handle > rest parameters already, so that clojure.core/maybe-destructured > doesn't actually need to do anything to top-level elements of the > binding vector: > > clojure.core> (maybe-destructured '[a b] ()) > ([a b]) > clojure.core> (maybe-destructured '[a & b] ()) > ([a & b]) > clojure.core> (maybe-destructured '[a [b & c]] ()) > ([a p__8059] (clojure.core/let [[b & c] p__8059])) > > Since & is a symbol, it's just passed right through and left to fn* to > deal with. But :as is not a symbol, so we end up with this: > > clojure.core> (maybe-destructured '[a :as b] ()) > ([a p__8064 b] (clojure.core/let [:as p__8064])) > > Is there a reason for this apparent irregularity? > > -- > Ben Wolfson > "Human kind has used its intelligence to vary the flavour of drinks, > which may be sweet, aromatic, fermented or spirit-based. ... Family > and social life also offer numerous other occasions to consume drinks > for pleasure." [Larousse, "Drink" entry] > -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
special case in binding vector syntax for function definitions?
Both of these work: user> (let [[x & y] [1 2]] [x y]) [1 (2)] user> (let [[x :as y] [1 2]] [x y]) [1 [1 2]] And this works: user> ((fn [x & y] [x y]) 1 2) [1 (2)] But this gives an exception (unsupported binding form): user> ((fn [x :as y] [x y]) 1 2) ; Evaluation aborted. I would have expected this to work and return [1 [1 2]], with y bound to the whole vector implicitly passed to the function (just as it's bound to the tail of the whole vector implicitly passed in the third case). This seems to happen because (apparently) the internals of fn* handle rest parameters already, so that clojure.core/maybe-destructured doesn't actually need to do anything to top-level elements of the binding vector: clojure.core> (maybe-destructured '[a b] ()) ([a b]) clojure.core> (maybe-destructured '[a & b] ()) ([a & b]) clojure.core> (maybe-destructured '[a [b & c]] ()) ([a p__8059] (clojure.core/let [[b & c] p__8059])) Since & is a symbol, it's just passed right through and left to fn* to deal with. But :as is not a symbol, so we end up with this: clojure.core> (maybe-destructured '[a :as b] ()) ([a p__8064 b] (clojure.core/let [:as p__8064])) Is there a reason for this apparent irregularity? -- Ben Wolfson "Human kind has used its intelligence to vary the flavour of drinks, which may be sweet, aromatic, fermented or spirit-based. ... Family and social life also offer numerous other occasions to consume drinks for pleasure." [Larousse, "Drink" entry] -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
