Maybe an Emacs script to expand the nodes nicely: http://www.youtube.com/watch?v=6ofEZQ7XoEA I don't find mere pretty printing that useful compared to the “expanding” paradigm I'm used to in Chrome and Firebug. To try it just M-x eval-buffer on these two files, http://www.emacswiki.org/emacs/download/peg.el https://raw.github.com/chrisdone/haskell-emacs/master/src/hs-show.el then make some fresh empty buffer with some demo Show output code: BinJab 1 (Biny 2 Leaf Leaf) (Binpo 3 Leaf Leaf) (Binamr 3 Leaf (Lalar 3 Leaf Leaf)) and try, maybe, M-: (hs-show-replace (point-min) (point-max)) you should get “BinJab”, and then clicking it will give you more until you have: http://i.imgur.com/a7rvz.png The parser is of course a PEG parser within elisp so it kind of sucks for large data structures (limited by Elisp's stack, and is super slow). My haskell-emacs package has it in the REPL but I want to replace this parser with a haskell-src-exts→sexp utility to make it faster and more reliable. If anyone wants to replace the parser (and indeed the "shower") as described, I'd be very happy as this is a Super Nice feature and indispensable in the REPL with “real” data. Ciao!