haskell - What is the nicest way to make a function that takes Float or Double as input? -
say want implement fermi function (the simplest example of logistic curve) if it's passed float returns float , if it's passed double returns double. here's i've got:
e = 2.7182845904523536 fermifunc :: (floating a) => -> fermifunc x = let 1 = fromintegral 1 in one/(one + e^(-x)) the problem ghc says e double. defining variable one kinda gross. other solution i've thought of define function doubles:
e = 2.7182845904523536 fermifuncdouble :: double -> double fermifuncdouble x = 1.0/(1.0 + e^(-x)) then using either:
fermifunc :: (floating a) => either float double -> fermifunc right x = double2float (fermifuncdouble (float2double x)) fermifunc left x = fermifuncdouble x this isn't exciting though because might have written separate function float case handles casting , calls fermifuncdouble. there nice way write function both types?
don't write e^x, ever, in language. not exponential function, it's power function.
the exponential function called exp, , definition has little power operation – it's defined, depending on taste, taylor series or the unique solution ordinary differential equation d⁄d𝑥 exp 𝑥 = exp 𝑥 boundary condition exp 0 = 1. now, happens that, rational n, have exp n ≡ (exp 1)n , motivates defining power operation numbers in ℝ or ℂ addition ℚ, namely as
az := exp (z · ln a)
...but e𝑥 should understood shortcut writing exp(𝑥) itself.
so rather defining e somewhere , trying take power of it, should use exp is.
fermifunc :: floating => -> fermifunc x = 1/(1 + exp (-x)) ...or indeed
fermifunc = recip . succ . exp . negate
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