3 ms·

This is cool but I still don't get how it is able to distinguish between linear, power, exponential, etc. sequences so easily. Would be incredibly interested in

• cygx 11y ago
  Linear and geometric sequences are auto-detected, for anything else you'll need to provide a function to compute the next element: 2, 4 ... * # linear 2, 4, 8 ... * # exponential 1, 1 ... * # constant 1, 1, * + * ... * # Fibonacci The last expression is equivalent to the more verbose variant 1, 1, -> $a, $b { $a + $b } ... * that makes use of an 'pointy block' (ie lambda function) instead of the Whatever-*.
  • joeyh 11y ago
    Ah so it's similar to the haskell list comprehension syntax, converted to a point-free form (and with added guessing/defaulting due to the ambiguities therein). [x*2 | x <- [1..10]] -- linear [2^x | x <- [1..10]] -- exponential [1 | x <- [1..10]] -- constant IIRC haskell list comprehensions can't do fib without naming the list so it can refer to itself. OTOH, these perl list comprehensions seems unable to express things that combine values from several lists, eg: [ x*y | x <- [2,4..8], y <- [-1,0,1] ] -- [-2,0,2,-4,0,4,-6,0,6,-8,0,8] Course, haskell also has a weak form of [x1,x2..xn] syntax for a linear sequence, as in [2,4..8]. That's always felt a bit of an unnecessary wart in haskell to me, although the simpler [x..y] and [x..] are very handy syntaxes. TBH, I almost never use list comprehensions either, preferring regular functions, and the list monad or applicative. (*2) [1..10] -- linear (2^) [1..10] -- exponential repeat 1 -- constant fibs = 0 : 1 : zipWith (+) fibs (tail fibs) -- fibonacci obvs (*) <$> [2,4..8] <*> [-1,0,1] -- same as [ x*y | x <- [2,4..8], y <- [-1,0,1] ]
    • raiph 11y ago
      Fwiw, the Haskell: [ x*y | x <- [2,4..8], y <- [-1,0,1] ] -- [-2,0,2,-4,0,4,-6, 0,6,-8,0,8] could be translated to the Perl 6: [2,4...8] X* [-1,0,1] # (-2 0 2 -4 0 4 -6 0 6 -8 0 8)
      • Kutta 11y ago
        Alternate pointfree Haskell syntax: (*) <$> [2,4..8] <*> [-1, 0, 1] or liftA2 (*) [2, 4..8] [-1, 0, 1]
      • joeyh 11y ago
        Sure, but that perl is not using the ... list comprehension syntax to combine the lists.
    • Grim_Reaper 11y ago
      Python list comprehension similar to Haskell -> https://en.wikipedia.org/wiki/List_comprehension#Python https://en.wikipedia.org/wiki/List_comprehension#Python
  • 1ris 11y ago
    This is so very Perl. I guess this is Perls answer to list comprehensions.
    • koenigdavidmj 11y ago
      I would assume that it has those too. Due to the main implementation being Pugs for a while, the language absorbed a lot of Haskellisms (chiefly laziness).
    • kbenson 11y ago
      That's interesting, I always figured Python's list comprehensions where their answer to Perl's map and grep. But in direct answer to your question, no, but it's part of the answer[1]. 1: https://en.wikipedia.org/wiki/List_comprehension#Perl_6 https://en.wikipedia.org/wiki/List_comprehension#Perl_6
    • dragonwriter 11y ago
      gather/take is more the general Perl 6 take on list comprehensions.