Programming Praxis

9 Responses to “Exercise 2-4”

1. James Curtis-Smith said

   January 20, 2017 at 12:12 PM

   As a perl user I would do this a perl way…

   sub squeeze {
     my $r = quotemeta $_[1];
     return my $y = $_[0] =~ s/[$r]//gr
   }
   
   print squeeze(@ARGV),"\n";
   
2. James Curtis-Smith said

   January 20, 2017 at 12:14 PM

   Perl golf would get it down to

   sub squeeze{return$_[0]=~s/[@{[quotemeta$_[1]]}]//gr}
   
3. matthew said

   January 20, 2017 at 12:40 PM

   Here’s some C++:

   #include <stdio.h>
   template <typename T, typename PRED>
   void filter(T *p, PRED pred) {
      for (T *q = p; *q != T(0); q++) {
         if (!pred(*q)) *p++ = *q;
      }
      *p = 0;
   }
   template <typename T>
   bool member(T a, T *p) {
      for ( ; *p != T(0); p++) {
         if (a == *p) return true;
      }
      return false;
   }
   void squeeze(char *s, char *t) {
      filter(s,[=](char c) { return member(c,t); });
   }
   
   int main(int argc, char *argv[]) {
      squeeze(argv[1],argv[2]);
      printf("%s\n", argv[1]);
   }
   
4. matthew said

   January 20, 2017 at 12:44 PM

   Or some more traditional C:

   #include <stdio.h>
   #include <stdbool.h>
   void f(char *s, const char *t) {
      int i = 0, j = 0, k = 0;
      while (true) {
         if (t[i] == 0) {
            i = 0; s[k++] = s[j++];
         } else if (s[j] == 0) {
            s[k++] = 0; break;
         } else if (t[i] == s[j]) {
            i = 0; j++;
         } else {
            i++;
         }
      }
   }
   
   int main(int argc, char *argv[]) {
      f(argv[1],argv[2]);
      printf("%s\n", argv[1]);
      return 0;
   }
   
5. Michael Vehrs said

   January 20, 2017 at 12:55 PM

   Guile:

   (define (squeeze str chars) (string-delete (string->char-set chars) str))
6. Jussi Piitulainen said

   January 20, 2017 at 1:04 PM

   Python strings have translation-table methods.

   >>> x = str.maketrans('','','aeiouyäö')
   >>> 'Pidä pää kylmänä ja lopeta twiittailu'.translate(x)
   'Pd p klmn j lpt twttl'
   
7. Globules said

   January 21, 2017 at 5:33 AM

   Here’s a Haskell version. It also works on any list whose elements support equality testing.

   -- Return a list consisting only of elements not contained in the first
   -- argument.
   squeeze2 :: Eq a => [a] -> [a] -> [a]
   squeeze2 del = filter (`notElem` del)
   
   main :: IO ()
   main = do
     putStrLn $ squeeze2 "pM" "Mississippi"
     print $ squeeze2 [2, 4] [1..5]
   

   $ ./squeeze 
   ississii
   [1,3,5]
   
8. matthew said

   January 22, 2017 at 11:33 AM

   @Globules: I was going to suggest

   import Control.Monad
   squeeze :: (Eq a, MonadPlus m) => [a] -> m a -> m a
   squeeze t = join . fmap nullset where
     nullset c
       | c `elem` t = mzero
       | otherwise = return c
   main = print $ squeeze "ace" "abcde"
   

   but really that is just your solution with mfilter instead of filter.
9. Globules said

   January 24, 2017 at 4:12 AM

   @matthew Your MonadPlus suggestion made me wonder what was the “most general” type I could give it. But then I got lost in a maze of twisty little typeclasses (Foldable, Alternative, etc.) and now I will just go to bed… :-)