Hi Conal,
On Sat, Jan 31, 2009 at 12:10 AM, Conal Elliott
Hopefully some enterprising Haskell hacker will wrap Cairo in a nice purely functional API.
Jefferson Heard is working on such a thing, called Hieroglyph. [...]
In the process, I realized more clearly that the *very goal* of making a purely functional wrapper around an imperative library leads to muddled thinking. It's easy to hide the IO without really eliminating it from the semantics, especially if the goal is defined in terms of an IO-based library. Much harder, and I think much more rewarding, is to design semantically, from the ground up, and then figure out how to implement the elegant semantics with the odds & ends at hand (like Cairo, OpenGL, GPU architectures, ...).
Exciting! I was very much trying to achieve this with Haven back in 2002: http://www.haskell.org/haven As the slides on that page state pretty explicitly, I tried to focus on the semantics and to design a purely functional representation of a vector graphics scene that was not tied to any particular implementation. My primary claim for success is that the representation of Picture in Haven type checks and doesn't appeal to IO; IO only creeps in when we attempt to render a Picture. Does the Haven API live up to your goal of semantic purity for a vector graphics library? If not, where specifically does it fall short? I look forward to seeing and reading more about Hieroglyph. The typography and visual presentation of Jefferson's online booklet looks fantastic. A high quality, purely functional vector graphics API for Haskell with portable and robust implementations will be a great thing for the Haskell world. Regards, -Antony