[Haskell-cafe] RE: Pretty Print, text or ++?

Paul Keir pkeir at dcs.gla.ac.uk
Fri Aug 15 10:07:20 EDT 2008

Awesome! Thanks to you all. I'll start with

hsep[map a, b, c, d]

and then I can try changing hsep for other things.


-----Original Message-----
From: Benedikt Huber [mailto:benjovi at gmx.net]
Sent: Fri 15/08/2008 14:53
To: Paul Keir
Cc: haskell-cafe at haskell.org
Subject: Re: Pretty Print, text or ++?
Paul Keir schrieb:
 > Hi there,
 > I'm writing a pretty printer using the Text.PrettyPrint library, and
 > there's a pattern I'm coming across quite often. Does anyone know 
 > text (a ++ b ++ c ++ d)
 > or
 > text a <+> text b <+> text c <+> text d
 > runs quicker?

Hi Paul,

 > text (a ++ b ++ c ++ d)

is the same as

 > hcat (map text [a,b,c,d])

(horizontal concatenation without seperating spaces)

 > text a <+> text b <+> text c <+> text d

corresponds to

 > hsep (map text [a,b,c,d])


 > text (unwords [a,b,c,d])

With <+>, hsep or hcat, pretty printing won't choose the best layout -
you tell the pretty printer to layout documents 'beside'.
For autolayout, see sep,cat and the paragraph-fill variants fsep and fcat.

Regarding performance: `unwords` will propably be a little faster 
(untested), but less flexible. There is no asymptotic overhead when 
using the pretty printer.


 > Cheers,
 > Paul
 > ------------------------------------------------------------------------
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 > Haskell-Cafe at haskell.org
 > http://www.haskell.org/mailman/listinfo/haskell-cafe

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