# Where is the pdf function in Distribution.jl implemented?

Hello Julia community,

julia> pdf(Normal(), 0.3)
0.38138781546052414


I want to know how the pdf function is implemented, but the source code for Distribution.jl tells me nothing (in fact it looks like an infinite loop).

Am I missing something? Wouldn’t there at least have to have a 2\pi somewhere?

julia-1.1> d = Normal()
julia-1.1> @less pdf(d, 0.3) # shows this is implemented via a macro, so try something else
julia-1.1> @code_lowered pdf(d,0.3)
CodeInfo(
1 ─ %1 = (Base.getproperty)(d, :μ)
│   %2 = (Base.getproperty)(d, :σ)
│   %3 = (Distributions.normpdf)(%1, %2, x)
└──      return %3
)

julia-1.1> @less Distributions.normpdf(0.0,1.0,0.3) # this is what you want


Page up to see your beloved constant.

2 Likes

In case it is not clear: pdf and other relevant functions are implemented in StatsFuns.jl.

2 Likes

Technically, functions are not implemented, methods are. What you linked are some generic fallback methods for dealing with some general cases (and the first one doesn’t look like a function definition at all, maybe a bug?).

You can also use

@edit pdf(Normal(), 0.3)


to take you to the source code (if your editor is set up properly).

In this case it takes you to a macro defining functions using primitives from StatsFuns, which I agree is rather opaque.