So last night I went to a Haskell workshop.

One of the examples my professor gave was the factorial function:

factorial :: (Num a, Eq a) => a -> a
factorial 0 = 1
factorial n = n * factorial(n-1)

The first line is the function signature, the second line is the base case, and the third line is the recursive step of the function. One thing I really like about Haskell so far is how clean recursive functions are.

Today I started dabbling a bit more with Haskell and created a recursive function to calculate pi using the Gregory–Leibniz formula:

pie :: (Integral a, Fractional b) => a -> b
pie 0 = 0
pie n = sign * 4 / (2 * (fromIntegral n) - 1) + pie(n-1)
  where sign = if even n then -1 else 1

I had to name it “pie” because “pi” was a reserved keyword. The “fromIntegral n” is there to allow an integer to be part of a fractional calculation. This is necessary because Haskell is über strict with types.

Here it is in action:

*Main> pie 1000
3.140592653839794
*Main> pie 10000
3.1414926535900345
*Main> pie 100000
3.1415826535897198

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