help for +=, .+, etcetera

[stevengj]

Operators like += and dotted operators like .+ currently don't have any REPL help.

[stevengj]

e.g. this works for += etcetera (from this list in the lowering code):

import Base.BaseDocs.Keyword
for op in (:+, :-, :*, :/, ://, :\, :^, :÷, :%, :<<, :>>,  :>>>, :|, :&, :⊻, :$)
    @eval @doc $("`x $op= y` is a synonym for `x = x $op y`")  $(Keyword(Symbol(op,"=")))
end

(Had to use the special Keyword wrapper since += does not parse as a valid identifier.)

(There are also "dotted" update operators like .+=.)

[stevengj]

Since things like .+ parse, in principle we could just add ordinary documentation strings for each dottable operator. However, that is a bit annoying since the list of dottable operators is long and the only canonical list is in julia-parser.scm, which is not directly accessible from Julia.

Instead, it might be better to modify the @repl macro (which is used by the REPL module to look up help) to check for dotted operators.

[stevengj]

(Removing the "good first issue" tag since getting into the guts of the documentation system like this is not very accessible to newbies.)

[stevengj]

We'll also want to document .= specially, since broadcast assignment is different from other broadcast operators.