Re: [Haskell-beginners] Flying Dutchman sailing blind

On Tue, Oct 5, 2010 at 1:46 PM, Stephen Tetley wrote:

On 5 October 2010 09:06, Jeroen van Maanen wrote:

...

P.S. For an idea of what is living in the snail pit, have a look at:

 http://lexau.svn.sourceforge.net/viewvc/lexau/branches/totem/src/LExAu/Pipel...  http://lexau.svn.sourceforge.net/viewvc/lexau/branches/totem/src/LExAu/Model...

(I know, HistoryTree.hs badly needs to be split up into smaller modules.)

A minor style tip...

You are using ShowS family functions (showString, showChar) to generate strings which is good as it avoids (++). However, to make the code clearer you might want to code up a little helper library with ShowS versions of the usual pretty print combinators.

e.g. all the functions like parens:

parens :: ShowS -> ShowS parens s = showChar '(' . s . showChar ')'

Having a library of these functions usually pays off (I think there is one on Hackage but I can't remember its name). You could use a pretty printing library, but they are somewhat less efficient as the have to do work measuring line lengths for fitting lines to screen width.

Best wishes

Stephen _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

Instead of a ShowS you might want to use a DString[1] which is basically a newtype wrapper around a ShowS. The advantage of a DString is that it has an instance for IsString which allows you to write overloaded string literals of type DString. You might also take a look at string-combinators[2] which provides handy polymorphic functions to build and combine string-like values. For example it provides: paren :: (Monoid s, IsString s) => s -> s (I've no idea why I named this 'paren' instead of 'parens' I will change this in the next version) Regards, Bas [1] http://hackage.haskell.org/package/dstring [2] http://hackage.haskell.org/package/string-combinators