[Haskell-cafe] Input and output of mathematical expressions

Greetings Cafe, What would you recommend as a Haskell-based means of interactively reading and writing mathematical formulae? As a toy example, what might I use to write a program which presents the user with Please simplify the expression: \pi x^2 + 3\pi x^2 (Where the TeX-style expression would be presented with a greek pi and superscript twos on the xs.) The user should then have the ability to reply with something that looks like the result of TeXing 5 \pi x^2 Whatever means the user uses to enter this expression, he should be able to preview the "typeset" version of his input before submitting. Any ideas? Thanks.