How to test if a module is already imported?

[Matt Bauman]

Is there a robust way to test if a Module has already been imported?  Some modules take a very long time to load, and in some contexts it might be nicer to check to see if the functionality is there before spending 30 seconds loading it and all its dependencies.

The naive :FooModule in names(Main) fails if I reference FooModule later in the same namespace.  I can get around that by adding another scope (like a macro or secondary function), but that's a bit of a pain.  Is there a better way?

julia> f() = :FooModule in names(Main) && (println("has FooModule"); FooModule.bar())

f (generic function with 1 method)

julia> f()

has FooModule

ERROR: FooModule not defined

 in f at none:1

[Alessandro "Jake" Andrioni]

A nicer hack would be to use the isdefined function:

julia> isdefined(:Stats)
false

julia> import Stats

julia> isdefined(:Stats)
true

[Kevin Squire]

Are you planning to load it if it isn't already loaded?  If so, there's no need to check--modules should only be loaded once, even if they're used/imported more than once.

Cheers,

   Kevin

[Matt Bauman]

No, my use case is to add some custom functionality to Gadfly within juliarc. Often I pre-compile Gadfly in userimg.jl, but not always. When it's not precompiled I don't particularly want to wait for it to load on every startup.

Pkg.on_load would be the perfect solution for this. But isdefined works great. Thanks Alessandro!