Where is 'findprev' located?

General Usage
1

I guess it is from the Base module.

How to find it out?

2

You can use the command methods(findprev) to see the files involved. There are multiple methods for this function in several files, depending on the input type.

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3

If you are unsure which of the methods from @steffenPL s call is actually called, you can use @which and it tells you which version it dispatches on

julia> @which findprev([false, false, true, false],3)
findprev(A, start)
     @ Base array.jl:2173
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4

And to slightly expand on @kellertuer’s answer: You can also use @edit to directly open the code definition in your favourite editor.

julia> @edit findprev([false, false, true, false],3)
#= editor opens =#
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5

unfortunately, it seems that these work only for some inbuilt functions of Julia. I am using a package written by some people, and neither @which nor @edit work for the functions in the package. I got

ERROR: expression is not a function call, or is too complex for @edit to analyze; break it down to simpler parts if possible. In some cases, you may want to use Meta.@lower.
Stacktrace:
 [1] error(s::String)
   @ Base .\error.jl:35
 [2] top-level scope
   @ REPL[8]:1
6

@jiang_ming_zhang can you give a complete example that we can try?

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7

As the error message states, I would also think that maybe the arguments of your function call are a bit too complex (maybe with nested function calls?)

Note that the whole @which command works for arbitrary packages and functions since all packages provide their code, so e.g.

julia> using JuliaFormatter
julia> @which format(".")
format(path::AbstractString; options...)
     @ JuliaFormatter ~/.julia/packages/JuliaFormatter/ddD3y/src/JuliaFormatter.jl:425

or also for packages in development mode

julia> using Manifolds
julia> @which Sphere(3)
Sphere(n::Int64)
     @ Manifolds ~/path-to-your-local-repo/src/manifolds/Sphere.jl:55
8

Or indeed for functions that the user just defined in a current session:

julia> f(x::Int) = 1
f (generic function with 1 method)

julia> f(x::Float64) = 1.0
f (generic function with 2 methods)

julia> @which f(1)
f(x::Int64)
     @ Main REPL[17]:1

julia> @which f(1.0)
f(x::Float64)
     @ Main REPL[18]:1
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