Re: drop-while for noobs
On 9 August 2010 22:16, Alan a...@malloys.org wrote: Weird. I wonder if I was using an outdated version of Clojure or (more likely) assumed from (doc drop-while) that it wouldn't handle false the way I wanted. When doc says not nil should I assume it means neither nil nor false, or should the doc for drop-while be updated? user= (doc drop-while) - clojure.core/drop-while ([pred coll]) Returns a lazy sequence of the items in coll starting from the first item for which (pred item) returns nil. I think the docs should be fixed to refer to logical false like other parts of the documentation, instead of nil. e.g.: (find-doc logical false) [...] clojure.core/when-not ([test body]) Macro Evaluates test. If logical false, evaluates body in an implicit do. nil -- Michael Wood esiot...@gmail.com -- 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
Re: drop-while for noobs
you can do this using partition.
let's assume I first define a
user= (def a [:w :n :e :s])
#'user/a
user= (partition 2 1 (conj a (first a)))
((:w :n) (:n :e) (:e :s) (:s :w))
gives you the pairs you need.
then you just need to turn it into hash-map
by doing
(map #(apply hash-map %) (partition 2 1 (conj a (first a
On Mon, Aug 9, 2010 at 3:09 PM, Alan a...@malloys.org wrote:
Hi all, I'm new to the group; I have some experience with both CL and
Java, though it's been a while for each. Anyway I really like Clojure
as a way of combining the best parts of the two languages, but I'm
still getting the hang of it and there are often things that confuse
me.
For example, I wanted to define a ring function, which takes as input
N objects, and returns a hash table mapping object N to object N+1
(mod N). I intended to use this to describe a compass object:
(ring :w :n :e :s) should result in {:w :n, :n :e, :e :s, :s :w}.
I could have done this with basic recursion or as a list comprehension
using (for), (count), and (rem), but it seemed there must be a more
elegant solution with lazy sequences, like maybe combining cycle and
map to gloss over the N==0 wraparound issue. What I came up with was
frankly a monstrosity; I don't have the source with me at work, but it
looked roughly like:
(defn ring [ elts]
(apply assoc {}
(map #(list
%1
(fnext (drop-while
(comp (partial or
(partial not= %1)
nil))
(cycle elts))
elts
Since then I've realized I could have used nth and map-indexed to get
a less ugly result, but I was baffled by the awkwardness of drop-
while: is there a reason it demands nil or not-nil, instead of
treating false and nil as logical false? Converting false to nil was a
real bear (and retyping this from memory I'm pretty sure my syntax for
comp/partial/or is wrong somewhere), and in my experience clojure is
too clever make me do crap like this; what am I missing?
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Re: drop-while for noobs
It works with booleans:
user= (drop-while neg? [-3 -2 -1 0 1 2 3 ])
(0 1 2 3)
user= (class (neg? -5))
java.lang.Boolean
On Aug 9, 12:09 pm, Alan a...@malloys.org wrote:
Hi all, I'm new to the group; I have some experience with both CL and
Java, though it's been a while for each. Anyway I really like Clojure
as a way of combining the best parts of the two languages, but I'm
still getting the hang of it and there are often things that confuse
me.
For example, I wanted to define a ring function, which takes as input
N objects, and returns a hash table mapping object N to object N+1
(mod N). I intended to use this to describe a compass object:
(ring :w :n :e :s) should result in {:w :n, :n :e, :e :s, :s :w}.
I could have done this with basic recursion or as a list comprehension
using (for), (count), and (rem), but it seemed there must be a more
elegant solution with lazy sequences, like maybe combining cycle and
map to gloss over the N==0 wraparound issue. What I came up with was
frankly a monstrosity; I don't have the source with me at work, but it
looked roughly like:
(defn ring [ elts]
(apply assoc {}
(map #(list
%1
(fnext (drop-while
(comp (partial or
(partial not= %1)
nil))
(cycle elts))
elts
Since then I've realized I could have used nth and map-indexed to get
a less ugly result, but I was baffled by the awkwardness of drop-
while: is there a reason it demands nil or not-nil, instead of
treating false and nil as logical false? Converting false to nil was a
real bear (and retyping this from memory I'm pretty sure my syntax for
comp/partial/or is wrong somewhere), and in my experience clojure is
too clever make me do crap like this; what am I missing?
--
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Re: drop-while for noobs
On Aug 9, 2:09 pm, Alan a...@malloys.org wrote:
Hi all, I'm new to the group
Welcome!
I wanted to define a ring function, which takes as input
N objects, and returns a hash table mapping object N to object N+1
(mod N). I intended to use this to describe a compass object:
(ring :w :n :e :s) should result in {:w :n, :n :e, :e :s, :s :w}.
Here's a quick way that seems pretty close to your original:
user (def x [:w :n :e :s])
#'user/x
user (zipmap x (rest (cycle x)))
{:s :w, :e :s, :n :e, :w :n}
- Jeff
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Re: drop-while for noobs
Also sorry the indentation is so awful. How do I get Google to let me
compose/edit in a fixed-width font?
On Aug 9, 12:09 pm, Alan a...@malloys.org wrote:
Hi all, I'm new to the group; I have some experience with both CL and
Java, though it's been a while for each. Anyway I really like Clojure
as a way of combining the best parts of the two languages, but I'm
still getting the hang of it and there are often things that confuse
me.
For example, I wanted to define a ring function, which takes as input
N objects, and returns a hash table mapping object N to object N+1
(mod N). I intended to use this to describe a compass object:
(ring :w :n :e :s) should result in {:w :n, :n :e, :e :s, :s :w}.
I could have done this with basic recursion or as a list comprehension
using (for), (count), and (rem), but it seemed there must be a more
elegant solution with lazy sequences, like maybe combining cycle and
map to gloss over the N==0 wraparound issue. What I came up with was
frankly a monstrosity; I don't have the source with me at work, but it
looked roughly like:
(defn ring [ elts]
(apply assoc {}
(map #(list
%1
(fnext (drop-while
(comp (partial or
(partial not= %1)
nil))
(cycle elts))
elts
Since then I've realized I could have used nth and map-indexed to get
a less ugly result, but I was baffled by the awkwardness of drop-
while: is there a reason it demands nil or not-nil, instead of
treating false and nil as logical false? Converting false to nil was a
real bear (and retyping this from memory I'm pretty sure my syntax for
comp/partial/or is wrong somewhere), and in my experience clojure is
too clever make me do crap like this; what am I missing?
--
You received this message because you are subscribed to the Google
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Note that posts from new members are moderated - please be patient with your
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For more options, visit this group at
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Re: drop-while for noobs
Weird. I wonder if I was using an outdated version of Clojure or (more
likely) assumed from (doc drop-while) that it wouldn't handle false
the way I wanted. When doc says not nil should I assume it means
neither nil nor false, or should the doc for drop-while be updated?
user= (doc drop-while)
-
clojure.core/drop-while
([pred coll])
Returns a lazy sequence of the items in coll starting from the first
item for which (pred item) returns nil.
On Aug 9, 1:01 pm, Armando Blancas armando_blan...@yahoo.com wrote:
It works with booleans:
user= (drop-while neg? [-3 -2 -1 0 1 2 3 ])
(0 1 2 3)
user= (class (neg? -5))
java.lang.Boolean
On Aug 9, 12:09 pm, Alan a...@malloys.org wrote:
Hi all, I'm new to the group; I have some experience with both CL and
Java, though it's been a while for each. Anyway I really like Clojure
as a way of combining the best parts of the two languages, but I'm
still getting the hang of it and there are often things that confuse
me.
For example, I wanted to define a ring function, which takes as input
N objects, and returns a hash table mapping object N to object N+1
(mod N). I intended to use this to describe a compass object:
(ring :w :n :e :s) should result in {:w :n, :n :e, :e :s, :s :w}.
I could have done this with basic recursion or as a list comprehension
using (for), (count), and (rem), but it seemed there must be a more
elegant solution with lazy sequences, like maybe combining cycle and
map to gloss over the N==0 wraparound issue. What I came up with was
frankly a monstrosity; I don't have the source with me at work, but it
looked roughly like:
(defn ring [ elts]
(apply assoc {}
(map #(list
%1
(fnext (drop-while
(comp (partial or
(partial not= %1)
nil))
(cycle elts))
elts
Since then I've realized I could have used nth and map-indexed to get
a less ugly result, but I was baffled by the awkwardness of drop-
while: is there a reason it demands nil or not-nil, instead of
treating false and nil as logical false? Converting false to nil was a
real bear (and retyping this from memory I'm pretty sure my syntax for
comp/partial/or is wrong somewhere), and in my experience clojure is
too clever make me do crap like this; what am I missing?
--
You received this message because you are subscribed to the Google
Groups Clojure group.
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Note that posts from new members are moderated - please be patient with your
first post.
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For more options, visit this group at
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Re: drop-while for noobs
When doc says not nil should I assume it means neither nil nor false Nope, false won't be taken as nil; in boolean expressions nil evaluates to false. drop-while's doc mentions only nil but since it's the predicate's return value it should be clear enough, I think. -- 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
