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From: Melzzzzz <mel@zzzzz.com>
Newsgroups: comp.lang.forth
Subject: Re: Unfeasible?
Date: Sun, 6 Dec 2015 01:01:33 +0100
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On Thu, 3 Dec 2015 20:22:07 -0000 (UTC)
"WJ" <w_a_x_man@yahoo.com> wrote:

> One has a function "get_list" that produces a list.
> He has another function "test" that determines whether
> a member of the list passes muster.
> He has a function "foo" that is used to transform
> an element of the list.
> 
> The task is to iterate through the list while
> printing each element with its index and collecting
> the transformations of the elements that fit the bill.
> 
> Wouldn't this be painful in the Toy Language (ANS Forth)?
> 
> Ruby:
> 
> def get_list; ('aa'..'zz').step(36).to_a ; end
> def test s; s == s.reverse ; end
> def foo x; x.upcase ; end
> 
> get_list.each_with_index.
>   grep->((x,i)){printf "%2d - %s\n", i, x; test x}{|x,_| foo x}
> 
>  0 - aa
>  1 - bk
>  2 - cu
>  3 - ee
>  4 - fo
>  5 - gy
>  6 - ii
>  7 - js
>  8 - lc
>  9 - mm
> 10 - nw
> 11 - pg
> 12 - qq
> 13 - sa
> 14 - tk
> 15 - uu
> 16 - we
> 17 - xo
> 18 - yy
>     ==>["AA", "EE", "II", "MM", "QQ", "UU", "YY"]  
> 
Haskell ;)

[bmaxa@maxa-pc haskell]$ ghc unfeasible.hs
[1 of 1] Compiling Main             ( unfeasible.hs, unfeasible.o )
Linking unfeasible ...
[bmaxa@maxa-pc haskell]$ ./unfeasible 
 0 - aa
 1 - bk
 2 - cu
 3 - ee
 4 - fo
 5 - gy
 6 - ii
 7 - js
 8 - lc
 9 - mm
10 - nw
11 - pg
12 - qq
13 - sa
14 - tk
15 - uu
16 - we
17 - xo
18 - yy

["AA","EE","II","MM","QQ","UU","YY"]
[bmaxa@maxa-pc haskell]$ cat unfeasible.hs
import Text.Printf
import Data.Char

get_list = takeEvery 36 [[a,b] | a <- ['a'..'z'], b <- ['a'..'z']]
    where
        takeEvery n (x:xs) = x : (takeEvery n $ drop (n-1) xs)
        takeEvery _ [] = []

main = do
    putStrLn $ unlines 
             $ map (\(a,b) -> printf "%2d - %s" (a::Int) b)
             $ zip [0..] get_list
    print $ map (map toUpper) $ filter (\x -> x == reverse x) get_list