Where did you read about that function? That source is very outdated: readall(io) was replaced by readstring(io) in Julia 0.5, and then readstring(io) was replaced by read(io, String) in Julia 0.7.
If you are using Julia 1.X you should use read(io, String).
Thank you, that explains why it has been driving me nuts. (I am on day 2 of testing Julia, so I naturally assume that if something is not working, it must be me doing something worng)
It was here: readall(filename::AbstractString) » Julia Functions, hit by Google.
Only after you mentioned it, did I notice that I’d hit a page that is not official documentation.
I will delete this post after a while so as to avoding further infesting google with hits to this deprecated function, and I will also try to add a comment on the page at jhub.com