Code Golf: Leibniz formula for Pi

Answer 1

Haskell

I got it down to 34 characters:

foldl subtract 4$map(4/)[3,5..9^6]

This expression yields 3.141596416935556 when evaluated.

Edit: here's a somewhat shorter version (at 33 characters) that uses foldl1 instead of foldl:

foldl1 subtract$map(4/)[1,3..9^6]

Edit 2: 9^6 instead of 10^6. One has to be economical ;)

Edit 3: Replaced with foldl' and foldl1' with foldl and foldl1 respectively—as a result of Edit 2, it no longer overflows. Thanks to ShreevatsaR for noticing this.