Remove duplicates in comint-mode command history

[Denis Bueno]

I've been programming in SML for a class I'm taking at school. This  
involved firing up Emacs and a sml-mode buffer with the source code,  
and another Emacs buffer with inferor-sml-mode, which uses comint.

Is there any way (simple, preferably, but otherwise is fine) to  
remove duplicate command history entries? When I hit M-p, I want to  
see the last *unique* command I typed, not the last 25 times I typed  
the command to run my program.

Ideas?

-Denis