default lambda symbol in emacs haskell mode?
Does anyone know how I can print λ instead of using haskell in emacs. I know that one can use haskell-font-lock-symbols, but I find the rest of them hard to read - the arrows are TOO small!
Is there a simple way of over-riding the rest of the keys?
You can do this:
(defun pretty-lambdas-haskell ()
(font-lock-add-keywords
nil `((,(concat "(" (regexp-quote "") ")")
(0 (progn (compose-region (match-beginning 1) (match-end 1)
,(make-char 'greek-iso8859-7 107))
nil))))))
(add-hook 'haskell-mode-hook 'pretty-lambdas-haskell)
This adds the lambda as a keyword, meaning that it won't appear in escape sequences in strings for example (TODO: this is not the case after changing a thing). The ,(make-char 'greek-iso8859-7 107) is of course equivalent to ?λ , but you must make sure that your Emacs init file is encoded as unicode in that case.
You can also enable full symbol font locking and use a better (read: with wider arrows) font, like Pragmata Pro, Inconsolata or Ubuntu Monospace. I use the following code to select a good font:
(defun font-existsp (font)
"Check to see if the named FONT is available."
(if (null (x-list-fonts font))
nil t))
(require 'cl)
(defun font-avail (fonts)
"Finds the available fonts."
(remove-if-not 'font-existsp fonts))
(defvar font-preferences
'("PragmataPro"
"Inconsolata"
"DejaVu Sans Mono"
"Bitstream Vera Sans Mono"
"Anonymous Pro"
"Menlo"
"Consolas"))
(unless (eq window-system nil)
(let ((fonts (font-avail font-preferences)))
(unless (null fonts)
(set-face-attribute
'default nil :font
(car fonts)))))
You can also solve the problem with something like
(eval-after-load 'haskell-font-lock
'(setq haskell-font-lock-symbols-alist
(delq nil
(mapcar (lambda (rewrite)
(if (member (car rewrite) '("->" "<-"))
nil rewrite))
haskell-font-lock-symbols-alist))))
which should keep all mappings except for the one that changes "->" into "→" and "<-" into "←".
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