Add geometric mean primitive

[sternj]

I'd like to add a geometric mean primitive to Insect and this seems like the first step! I've never seen Purescript before now so this is probably going to be quite broken.

[sternj]

So I've realized that I just... can't do division? please advise

[sternj]

Okay, so the code that I have is

geomean ∷ NonEmptyList Quantity → Result
geomean xs = (_ `pow` ( one / n)) <$> foldM (⊗) (head xs) (tail xs)
  where
    n = Decimal.fromInt (length xs)

and the error at hand is

at src/Data/Quantity/Math.purs:183:45 - 183:48 (line 183, column 45 - line 183, column 48)

  Could not match type
            
    Quantity
            
  with type
               
    t2 Quantity
               

while checking that type Quantity -> Quantity -> Quantity
  is at least as general as type t0 -> t1 -> t2 t0
while checking that expression qMultiply
  has type t0 -> t1 -> t2 t0
in value declaration geomean

where t2 is an unknown type
      t1 is an unknown type
      t0 is an unknown type

[sharkdp]

Thank you very much for creating this — and sorry for not getting back to you earlier. I have been working on a rewrite of Insect over the past year. I will likely not make further updates to Insect. If you are still interested in this feature, maybe you could add it to Numbat instead? (https://github.com/sharkdp/numbat)

There are three places to look (following the example of mean):

• Actual implementation: https://github.com/sharkdp/numbat/blob/edc96d7e7bbd7a81ff7dbb9f5b7e501ccbfd4247/numbat/src/ffi.rs#L640-L657
• Register the function: https://github.com/sharkdp/numbat/blob/edc96d7e7bbd7a81ff7dbb9f5b7e501ccbfd4247/numbat/src/ffi.rs#L276-L283
• Add the function to the prelude: https://github.com/sharkdp/numbat/blob/edc96d7e7bbd7a81ff7dbb9f5b7e501ccbfd4247/numbat/modules/math/functions.nbt#L47