Ah thanks, I was aware of artist-mode, I thought there was some ESS like package that could output ascii graphs of functions :) R-fiddle is new to me though, thanks for that.
There's also orgtbl-ascii-plot[0], there was a mode for writing out flow diagrams in Emacs that used a web backend to render them (I don't remember the name), and I'm pretty sure you could abuse some graphics-to-ascii or DOT file command line tools to get the required result in Emacs buffer - particularly via org-babel, which lets you invoke external programs to "evaluate" code blocks. I remember using some Java-based local tool to render graphs through org-babel, but again I don't recall the name or URL.
[0] - http://orgmode.org/worg/org-contrib/orgtbl-ascii-plot.html