Dear Brad,
Thanks very much for the answer. I have been playing with your examples in the
code below (and learned a lot!). Based on your insight, I would suggest these
solutions to be added to the wikipedia:
https://en.wikipedia.org/wiki/Set-builder_notation#Parallels_in_programming_languages
Example1: Set.new: gather { for L { take $_ } };
Example2: Set.new: cross( K, X.grep: P(x) );
Cheers!
<--- Working code
my \L = 1..10; my \K = 1..10; my \X = 5..15;
# Example 1
my $e1 = Set.new: gather { for L { take $_ } };
# Example 2
my $s1 = Set.new: gather {
for K -> \k {
for X -> \x {
if x < 8 {
take (k,x);
}
}
}
}
my $s2 = Set.new: (K X[,] X).grep: -> ( \k, \x ) { x < 8 };
my $s3 = Set.new: ( -> \x { |(-> \k { (k,x) if x < 8 } for K) } for X );
my $s4 = Set.new: gather { -> \k { -> \x { take (k,x) if x < 8; } for X } for K
}
my $s5 = Set.new: cross( K, X.grep: * < 8 );
say $e1; say $s1; say $s2; say $s3; say $s4; say $s5;
<---
El Sunday, 10 de February del 2019 a les 12:05, Brad Gilbert va
escriure:
In
{l for l in L}
The reason it is in `{}` is to create a Set from iterating over `L`.
In Python, the set-builder's braces are replaced with square brackets,
parentheses, or curly braces, giving list, generator, and set objects,
respectively.
So in Python:
[ l for l in L ] gives a list
( l for l in L ) gives a generator
{ l for l in L } gives a set
In Perl6 those would most likely be written as:
L.List or L.Array or L.list
L.Seq
L.Set
---
The way to do that is
my \L = ((1..10) xx 3).flat.pick(*).list;
set( L ) # A
L.Set # B
my %set is SetHash;
{ ++%set{$_} for L } # C
# D
do {
# add the {} syntax to create a Set (lexically)
my sub circumfix:«{ }» ( \L ) { L.Set };
{ $_ for L } # <--
}
Something that seems similar to me is `unique`
.say for L.unique;
By that I mean, some places where you would use a Set, it makes sense
to use `.unique` instead
---
As for `{(k, x) for k in K for x in X if P(x)}`
The easiest one to directly translate appears to be the Scala one
my \K = 1..10;
my \X = 5..15;
# for (k <- K; x <- X if P(x)) yield (k,x)
Set.new: gather {
for K -> \k {
for X -> \x {
if P(x) {
take (k,x);
}
}
}
}
Other ways:
Set.new: (K X[,] X).grep: -> ( \k, \x ) { P(x) }
Set.new: K X[,] X.grep: &P
Set.new: K X[,] X.grep: &P
Set.new: ( -> ( \k, \x ) { (k,x) if P(x) } for K X[,] X )
Set.new: ( -> \x { |(-> \k { (k,x) if P x } for K) } for X)
On Sun, Feb 10, 2019 at 10:26 AM mimosinnet <mimosin...@gmail.com> wrote:
Hi all,
I wonder what would be the Perl notation for 'set-builders', as exposed
in this wikipedia article:
https://en.wikipedia.org/wiki/Set-builder_notation#Parallels_in_programming_languages
This is the Python notation:
Example 1: {l for l in L}
Example 2: {(k, x) for k in K for x in X if P(x)}
This is another example in Python:
s = {v for v in 'ABCDABCD' if v not in 'CB'}
https://en.wikipedia.org/wiki/List_comprehension#Similar_constructs
I have been playing with the code below. Nevertheless, I am unsure on
how to use the code to define a set.
Cheers!
<--- Code
#!/usr/bin/env perl6
my @L = 1 .. 10;
my @K = 1 .. 10;
my @X = 5 .. 15;
say "Example 1:";
for @L -> $l {
print "$l " if $l ∈ @L;
}
say "\nExample 2:";
for @K -> $k { for @X -> $x {
print "($k, $x), " if ($k ∈ @K and $x ∈ @X and $x < 8);
}}
<---
--
(≧∇≦) Mimosinnet (Linux User: #463211)
--
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