This works, except for the case where '=' appears more than twice consecutively. A string of multiple '=' should be treated as a single '='.<br><br><div class="gmail_quote">On Thu, Apr 29, 2010 at 16:26, Ozgur Akgun <span dir="ltr"><<a href="mailto:ozgurakgun@gmail.com">ozgurakgun@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">I won't attempt writing a general-case function now. If I understood your (rather long) description correctly, you want to<br>
- subtract 42 from the ascii value of the char, except when it is preceeded by '=', in which case you subtract 106 instead.<br>
<br><span style="font-family:courier new,monospace">foo :: [Char] -> [Char]</span><br style="font-family:courier new,monospace"><span style="font-family:courier new,monospace"><span style="font-family:courier new,monospace">foo ('=':x:xs) = chr (ord x - 106) : foo xs</span><br style="font-family:courier new,monospace">
foo (x:xs) = chr (ord x - 42) : foo xs<br>foo _ = []<br><br style="font-family:arial,helvetica,sans-serif"><span style="font-family:arial,helvetica,sans-serif">Hope I understood the problem correctly.</span><br style="font-family:arial,helvetica,sans-serif">
<span style="font-family:arial,helvetica,sans-serif">Best,</span><br><br></span><div><div></div><div class="h5"><div class="gmail_quote">On 29 April 2010 20:37, Jean-Nicolas Jolivet <span dir="ltr"><<a href="mailto:jeannicolascocoa@gmail.com" target="_blank">jeannicolascocoa@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex">First I would like to thank everyone for the very interesting replies and suggestions I got so far!...<br>
<br>
I tried to implement (and at the very least understand) most of them!...<br>
<br>
To add to the context here, what I am trying to do is:<br>
<br>
-apply a "transformation" to a character (in my case, subtracting 42 to its ASCII value, which I obtain with chr(ord(c) - 42)<br>
-if the character is preceded by a specific character (that would be, an escape character, in this case '=') then subtract 106 to its value instead of 42...<br>
-if the character is the escape character itself, '=', then skip it altogether (keeping in mind that the next character needs to be escaped)...<br>
<br>
I managed to do it, however I'm not totally satisfied in the way I did it... the problem was that... as I just explained, in some cases, the character that is being processed has to be "skipped" (and by that I mean, not added to the resulting string). This happens when the processed character IS the escape character...<br>
<br>
What I did was to build a List of Maybe Char.... my function does the proper operation on the character and returns a "Just Char" when the character is processed, or Nothing when it is the escaped character... so basically I would end up with something like: [Just 'f', Just 'o', Just 'o', Nothing]... I am mapping this using mapMaybe to end up with a proper String...<br>
<br>
Would there be any more efficient way of doing this? Considering that the escape character should NOT be added to the resulting string, is there any way I can avoid using the Maybe monad?<br>
<br>
Once again, thanks everyone for all the suggestions!<br>
<font color="#888888"><br>
Jean-Nicolas Jolivet<br>
</font><div><div></div><div><br>
On 2010-04-28, at 10:56 AM, Jean-Nicolas Jolivet wrote:<br>
<br>
> Hi there!<br>
><br>
> I'm trying to iterate through each character of a string (that part I<br>
> can do!) however, I need to apply a transformation to each<br>
> character...based on the previous character in the string! This is the<br>
> part I have no clue how to do!<br>
><br>
> I'm totally new to Haskell so I'm pretty sure I'm missing something<br>
> obvious... I tried with list comprehensions...map... etc... but I<br>
> can't figure out how I can access the previous character in my string<br>
> in each "iteration".... to use simple pseudo code, what i need to do<br>
> is:<br>
><br>
> while i < my_string length:<br>
> if my_string[i-1] == some_char:<br>
> do something with my_string[i]<br>
> else<br>
> do something else with my_string[i]<br>
><br>
> I'm using imperative programming here obviously since it's what I am<br>
> familiar with...but any help as to how I could "translate" this to<br>
> functional programming would be really appreciated!<br>
><br>
><br>
> Jean-Nicolas Jolivet<br>
<br>
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</div></div></blockquote></div><br><br clear="all"><br></div></div>-- <br><font color="#888888">Ozgur Akgun<br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>mac<br>