I’m very fond of the notion of Concatenative Languages such as Joy,
Factor…
Joy (programming language) - Wikipedia
http://www.latrobe.edu.au/philosophy/phimvt/joy/jp-joyjoy.html
http://factorcode.org/
There is a supreme simplicity about them.
So while reading what the current state of them is, I stumbled across
the notion of Point free (sometimes called Pointless) programming.
The idea of sequences of function compositions that elide the
arguments that they will be applied to.
http://www.haskell.org/haskellwiki/Pointfree
One can easily define a sequence of methods in Ruby…
fun_seq = [:a, :b, :c]
as a sequence of symbols.
Which one could apply to an arbitrary argument…
irb
f = [:to_s, :succ]
=> [:to_s, :succ]
f.inject(4,:send)
=> “5”
Oooh! Looky! That’s sneaky of me!
symbol_sequence.inject(arg,:send)
[:a, :b, :c].inject(arg,:send)
that’s equivalent to
arg.a.b.c
Not quite function composition. Cute, but let’s try…
irb
def a(a)
p [“a”,a]
a+“a”
end
=> nil
def b(b)
p [“b”,b]
b+“b”
end
=> nil
def c(c)
p [“c”,c]
c+“c”
end
=> nil
f=[:a,:b,:c]
=> [:a, :b, :c]
f.inject(“foo”){|memo,obj|send(obj,memo)}
[“a”, “foo”]
[“b”, “fooa”]
[“c”, “fooab”]
=> “fooabc”
[:a, :b, :c].inject(arg){|memo,obj|send(obj,memo)}
is equivalent to
c(b(a(arg)))
c(b(a(“bah”)))
[“a”, “bah”]
[“b”, “baha”]
[“c”, “bahab”]
=> “bahabc”
Or how about working with lambda’s or Proc objects…
a1 = lambda {|x| x+“a”}
=> #Proc:0xb7d9f744@:41(irb)
b1 = lambda {|x| x+“b”}
=> #Proc:0xb7e0feb8@:42(irb)
c1 = lambda {|x| x+“c”}
=> #Proc:0xb7dfa5e0@:43(irb)
[a1, b1, c1]
=> [#Proc:0xb7d9f744@:41(irb), #Proc:0xb7e0feb8@:42(irb),
#Proc:0xb7dfa5e0@:43(irb)]
[a1, b1, c1].inject(“foo”){|memo,proc| proc.call(memo)}
=> “fooabc”
Anyhoo! Clearly in principle one can do Pointfree programming Ruby.
Questions for the Group:
-
Is there a neater way of expressing a sequence of function
compositions in Ruby? -
Which Ruby Pointfree sequences are actually useful?
John C. Phone : (64)(3) 358 6639
Tait Electronics Fax : (64)(3) 359 4632
PO Box 1645 Christchurch Email : [email protected]
New Zealand