[Haskell-cafe] Input and output of mathematical expressions

[Jacek Generowicz]

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.