Precision problem

[Michael Marte]

When adding the three double numbers 
0.7, 0.2, and 0.1, a ghc 4.07-compiled program (compilation flag -O)
yields 0.9999999999999999. Whatever this string stands for, the number is
considered to be < 1.0, which breaks my program. What to do?

Thank you,
Michael Marte