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copied!<p><em>Caveat:</em> I'm not a Haskell user, so take this with a grain of salt.</p> <p>When you press <kbd>RET</kbd> after the <code>Hello</code>, Emacs doesn't know you're going to add a <code>|</code> (<a href="http://en.wikibooks.org/wiki/Haskell/Type_declarations" rel="nofollow">quick search</a> shows you can have other symbols). The Haskell folks have deemed the proper indentation to be lined up directly below the <code>H</code> in <code>Hello</code>. If the indentation were to automatically line up with the <code>|</code> on the line above, then all the cases where you <em>don't</em> type a <code>|</code> will result in improper indentation. Damned if you do, damned if you don't...</p> <p>Other programming modes (C/C++, Lisp, Tcl, ...) have the same problem - they cannot know ahead of time what you're going to put on the next line, so the indentation my not be what you'd hoped for.</p> <p>One solution is to use <a href="http://www.gnu.org/software/emacs/manual/html_node/emacs/Electric-C.html" rel="nofollow">"electric"</a> keys, which is to say that they insert characters and also force re-indentation. You could easily define <kbd>|</kbd> to be electric with the following code:</p> <pre><code>(defun haskell-electric-| () "it's electric! (insert | and indent as long as the | follows whitespace)" (interactive) (insert "|") (if (string-match-p "^\\s-*|" (buffer-substring (line-beginning-position) (point))) (haskell-indentation-indent-line))) (define-key haskell-mode-map "|" 'haskell-electric-|) </code></pre> <p>I added a check to ensure that the <code>|</code> inserted is preceded by only whitespace, you can customize that however you want or remove the check altogether.</p> <p>I presume there might also be other symbols in Haskell that would be worth making electric.</p>

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