[julia-users] How to test if a type is concrete?

[jw3126]

How to check if a Type is concrete? e.g. 
 
isconcrete(Array{Float64, 1})
true
isconcrete(Int)
false


Also is there an established way to check if the return value of a function 
is type stable for given input? (e.g. check if @code_warntype shows return 
type in ALL CAPS.)