Re: LoL which style for Clojure
Way back when I started with Clojure i was doing this:
(let [constant-data (something-expensive)]
(defn my-fn [x]
(do-something-with x constant-data)))
But was advised instead to do this:
(def my-fn
(let [constant-data (something-expensive)]
(fn [x]
(do-something-with x constant-data
So, there's that (third) option as well.
// ben
On Sat, Mar 23, 2013 at 9:56 AM, Marko Topolnik marko.topol...@gmail.comwrote:
What if there's some computation in there, but such that should be
performed at compile time? I still prefer the outside let whenever I want
to make dead sure it's not getting reallocated on each call. If there was
some well-specified and easily understood guarantee (for example, like the
one Java has for compile-time constants), only then I would prefer the
inner let.
On Friday, March 22, 2013 8:05:10 PM UTC+1, Laurent PETIT wrote:
2013/3/22 jamieorc jami...@gmail.com
Curious which style is preferred in Clojure and why:
(defn f1 []
(let [x {:foo 1 :bar 2 :baz 3}]
(keys x)))
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f2 []
(keys x)))
In either case, AFAIK, the compiler will recognize {:foo 1 :bar 2 :baz 3}
as constant and will only create it once when compiling.
First version is preferred.
Cheers,
Jamie
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Re: LoL which style for Clojure
Doug Hoyte's book Let Over Lambda—50 Years of Lisp devotes its very title
to the technique of (let...(fn...)).
On Friday, March 22, 2013 2:59:43 PM UTC-4, jamieorc wrote:
Curious which style is preferred in Clojure and why:
(defn f1 []
(let [x {:foo 1 :bar 2 :baz 3}]
(keys x)))
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f2 []
(keys x)))
Cheers,
Jamie
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Re: LoL which style for Clojure
On Sunday, March 24, 2013 10:53:28 AM UTC+1, bsmith.occs wrote: Way back when I started with Clojure i was doing this: (let [constant-data (something-expensive)] (defn my-fn [x] (do-something-with x constant-data))) But was advised instead to do this: (def my-fn (let [constant-data (something-expensive)] (fn [x] (do-something-with x constant-data The problem with this is that it gets messy when setting up metadata is involved. -- -- 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 --- You received this message because you are subscribed to the Google Groups Clojure group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
Re: LoL which style for Clojure
What if there's some computation in there, but such that should be
performed at compile time? I still prefer the outside let whenever I want
to make dead sure it's not getting reallocated on each call. If there was
some well-specified and easily understood guarantee (for example, like the
one Java has for compile-time constants), only then I would prefer the
inner let.
On Friday, March 22, 2013 8:05:10 PM UTC+1, Laurent PETIT wrote:
2013/3/22 jamieorc jami...@gmail.com javascript:
Curious which style is preferred in Clojure and why:
(defn f1 []
(let [x {:foo 1 :bar 2 :baz 3}]
(keys x)))
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f2 []
(keys x)))
In either case, AFAIK, the compiler will recognize {:foo 1 :bar 2 :baz 3}
as constant and will only create it once when compiling.
First version is preferred.
Cheers,
Jamie
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Re: LoL which style for Clojure
Just out of curiosity, does it have to be a function?
(def data {:foo 1 :bar 2 :baz 3})
(def data-keys (keys data))
If one item is constant the other probably is too?
Cheers,
/thomas
On Friday, March 22, 2013 7:59:43 PM UTC+1, jamieorc wrote:
Curious which style is preferred in Clojure and why:
(defn f1 []
(let [x {:foo 1 :bar 2 :baz 3}]
(keys x)))
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f2 []
(keys x)))
Cheers,
Jamie
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Re: LoL which style for Clojure
On Sat, Mar 23, 2013 at 4:16 AM, Thomas Heller th.hel...@gmail.com wrote:
Just out of curiosity, does it have to be a function?
(def data {:foo 1 :bar 2 :baz 3})
(def data-keys (keys data))
If one item is constant the other probably is too?
In this case, yes, but it's easy to imagine cases where neither is a constant.
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Re: LoL which style for Clojure
def/defn et. al are top-level form definitions...very rarely (I'd say
never) you'd have a def/defn inside a 'let' or inside anything for that
matter...The 1st one looks good :)
Jim
On 22/03/13 18:59, jamieorc wrote:
Curious which style is preferred in Clojure and why:
(defn f1 []
(let [x {:foo 1 :bar 2 :baz 3}]
(keys x)))
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f2 []
(keys x)))
Cheers,
Jamie
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Re: LoL which style for Clojure
2013/3/22 jamieorc jamie...@gmail.com
Curious which style is preferred in Clojure and why:
(defn f1 []
(let [x {:foo 1 :bar 2 :baz 3}]
(keys x)))
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f2 []
(keys x)))
In either case, AFAIK, the compiler will recognize {:foo 1 :bar 2 :baz 3}
as constant and will only create it once when compiling.
First version is preferred.
Cheers,
Jamie
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Re: LoL which style for Clojure
Thanks, that's what I expected, especially after doing some (time... )
experiments.
On Friday, March 22, 2013 3:05:10 PM UTC-4, Laurent PETIT wrote:
2013/3/22 jamieorc jami...@gmail.com javascript:
Curious which style is preferred in Clojure and why:
(defn f1 []
(let [x {:foo 1 :bar 2 :baz 3}]
(keys x)))
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f2 []
(keys x)))
In either case, AFAIK, the compiler will recognize {:foo 1 :bar 2 :baz 3}
as constant and will only create it once when compiling.
First version is preferred.
Cheers,
Jamie
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Re: LoL which style for Clojure
For the example given, I would say it depends on what you are trying to
express.
The function f1 is a function that needs some internal data x to operate
-x might be considered an implementation detail.
The function f2 operates on well known data x -x might be considered
configuration of f2 or a more general concept.
Use both appropriately to write more expressive code -constraining yourself
to only one is like taking some of the colors off your palette.
In addition to the expression differences, there are two closely related
issues that should be considered:
1. There is a difference in the evaluation semantics. In the first
example, the form bound to x is evaluated every time f1 is called. In the
second, the form is invoked just once (at compile time) and then closed
over by f2. That can have very real consequences in real world apps
(performance, side-effects). In simple cases where the form is effectively
constant (as in your example), the compiler may optimize things such that
the costs are equivalent -but I don't think that's a guarantee, especially
on different runtimes (CLR, ClojureScript, etc).
2. There is a scope difference between the two. The second approach allows
you to close over x with multiple functions:
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f3 []
(keys x))
(defn f4 []
(vals x)))
-Chris
On Friday, March 22, 2013 2:59:43 PM UTC-4, jamieorc wrote:
Curious which style is preferred in Clojure and why:
(defn f1 []
(let [x {:foo 1 :bar 2 :baz 3}]
(keys x)))
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f2 []
(keys x)))
Cheers,
Jamie
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Re: LoL which style for Clojure
I've certainly seen this at least a few spots within the 4clojure codebase –
https://github.com/4clojure/4clojure/blob/develop/src/foreclojure/utils.clj#L66-L70
(quick example, I believe there are more)
On Friday, March 22, 2013 3:02:20 PM UTC-4, Jim foo.bar wrote:
def/defn et. al are top-level form definitions...very rarely (I'd say
never) you'd have a def/defn inside a 'let' or inside anything for that
matter...The 1st one looks good :)
Jim
On 22/03/13 18:59, jamieorc wrote:
Curious which style is preferred in Clojure and why:
(defn f1 []
(let [x {:foo 1 :bar 2 :baz 3}]
(keys x)))
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f2 []
(keys x)))
Cheers,
Jamie
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Re: LoL which style for Clojure
The question should probably be asked: is there a benefit in a given
situation to having the let be outside the scope of the defn? I would argue
that most times it is not, and putting the let outside the function
clutters the code and makes it harder to see the functions defined in the
namespace. If you truly need a const value, then something like this is
better, IMO:
(def ^:private ^:const data {:a 1 :b 2})
(defn f1 [])
(defn f2 [])
I would say that most of the time, the let at the top version could be
refactored into a def with no change in semantics, while at the same time
gaining a bonus to readability.
On Fri, Mar 22, 2013 at 2:41 PM, Robert Pitts rbxbx...@gmail.com wrote:
I've certainly seen this at least a few spots within the 4clojure codebase
–
https://github.com/4clojure/4clojure/blob/develop/src/foreclojure/utils.clj#L66-L70(quick
example, I believe there are more)
On Friday, March 22, 2013 3:02:20 PM UTC-4, Jim foo.bar wrote:
def/defn et. al are top-level form definitions...very rarely (I'd say
never) you'd have a def/defn inside a 'let' or inside anything for that
matter...The 1st one looks good :)
Jim
On 22/03/13 18:59, jamieorc wrote:
Curious which style is preferred in Clojure and why:
(defn f1 []
(let [x {:foo 1 :bar 2 :baz 3}]
(keys x)))
(let [x {:foo 1 :bar 2 :baz 3}]
(defn f2 []
(keys x)))
Cheers,
Jamie
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