Comments on: Parsing annotated postfix operators with Haskell http://www.hvergi.net/2008/07/parsing-annotated-postfix-operators-with-haskell/ Just another programming weblog Tue, 06 Jan 2009 21:52:27 +0000 http://wordpress.org/?v=2.5.1 By: imobi http://www.hvergi.net/2008/07/parsing-annotated-postfix-operators-with-haskell/#comment-1220 imobi Mon, 05 Jan 2009 05:18:22 +0000 http://www.hvergi.net/?p=30#comment-1220 <p><strong>greatings...</strong></p> <p>Great job. But not enought info. Where can i read more?...</p> greatings…

Great job. But not enought info. Where can i read more?…

]]> By: Recent URLs tagged Parsers - Urlrecorder http://www.hvergi.net/2008/07/parsing-annotated-postfix-operators-with-haskell/#comment-1157 Recent URLs tagged Parsers - Urlrecorder Sun, 28 Dec 2008 00:16:25 +0000 http://www.hvergi.net/?p=30#comment-1157 <p>[...] recorded first by Gaarafan220 on 2008-12-16→ Parsing annotated postfix operators with Haskell [...]</p> [...] recorded first by Gaarafan220 on 2008-12-16→ Parsing annotated postfix operators with Haskell [...]

]]> By: Websites tagged "parsing" on Postsaver http://www.hvergi.net/2008/07/parsing-annotated-postfix-operators-with-haskell/#comment-452 Websites tagged "parsing" on Postsaver Thu, 16 Oct 2008 21:47:21 +0000 http://www.hvergi.net/?p=30#comment-452 <p>[...] - Parsing annotated postfix operators with Haskell saved by rideonjp2008-10-16 - When the Passion for Search Technology meets the Logic of Inquiry. [...]</p> [...] - Parsing annotated postfix operators with Haskell saved by rideonjp2008-10-16 - When the Passion for Search Technology meets the Logic of Inquiry. [...]

]]> By: Arnar http://www.hvergi.net/2008/07/parsing-annotated-postfix-operators-with-haskell/#comment-54 Arnar Thu, 24 Jul 2008 18:54:10 +0000 http://www.hvergi.net/?p=30#comment-54 <p>Daniel, thanks, but that wouldn't work here as <code>adapters</code> may be the empty list.</p> Daniel, thanks, but that wouldn’t work here as adapters may be the empty list.

]]> By: Daniel Lyons http://www.hvergi.net/2008/07/parsing-annotated-postfix-operators-with-haskell/#comment-52 Daniel Lyons Thu, 24 Jul 2008 18:00:52 +0000 http://www.hvergi.net/?p=30#comment-52 <p>Micro-optimization: you could use <code>foldr1</code> instead, and omit <code>id</code>. :)</p> Micro-optimization: you could use foldr1 instead, and omit id. :)

]]> By: misterbeebee http://www.hvergi.net/2008/07/parsing-annotated-postfix-operators-with-haskell/#comment-51 misterbeebee Thu, 24 Jul 2008 17:57:00 +0000 http://www.hvergi.net/?p=30#comment-51 <p>You could call it "stackApply", since it applies the listed functions in a stack on top of the argument.</p> You could call it “stackApply”, since it applies the listed functions in a stack on top of the argument.

]]> By: Arnar http://www.hvergi.net/2008/07/parsing-annotated-postfix-operators-with-haskell/#comment-48 Arnar Thu, 24 Jul 2008 11:03:52 +0000 http://www.hvergi.net/?p=30#comment-48 <p>Hey Amicia,</p> <p>Again, with some helps from the folks at #haskell: There is no name for it, but this turns out to be <code>mconcat</code> for a monoid called <code>Endo a</code>. Conceptually that is the monoid for <code>a -> a</code>, i.e. it has unit <code>id</code> and operator <code>(.)</code>. Well, almost...</p> <p><code>mconcat [Endo f, Endo g] `appEndo` x</code></p> <p>gives you <code>f (g x)</code> so it is the reverse order of what we want. That is solved by using <code>Dual (Endo a)</code> instead:</p> <p><code>(appEndo . getDual . mconcat . map (Dual . Endo)) [f, g] x</code></p> <p>will give you <code>g (f x)</code> which is what we want.</p> <p>Examples are courtesy of EvilTerran</p> Hey Amicia,

Again, with some helps from the folks at #haskell: There is no name for it, but this turns out to be mconcat for a monoid called Endo a. Conceptually that is the monoid for a -> a, i.e. it has unit id and operator (.). Well, almost…

mconcat [Endo f, Endo g] `appEndo` x

gives you f (g x) so it is the reverse order of what we want. That is solved by using Dual (Endo a) instead:

(appEndo . getDual . mconcat . map (Dual . Endo)) [f, g] x

will give you g (f x) which is what we want.

Examples are courtesy of EvilTerran

]]> By: Amicia Pyn http://www.hvergi.net/2008/07/parsing-annotated-postfix-operators-with-haskell/#comment-46 Amicia Pyn Thu, 24 Jul 2008 08:12:35 +0000 http://www.hvergi.net/?p=30#comment-46 <p>Why isn't there a name for <code>foldr (flip (.)) id</code>? Or is there?</p> Why isn’t there a name for foldr (flip (.)) id? Or is there?

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