Implement convenience functions in Julia and in GAP for doing many common basic operations

[fingolfin]

It would be very convenient if there were default Julia implementations for getindex, setindex!, getproperty, setproperty! that work on any GapObj (and raise an error if not applicable).

Here is some untested rough draft (without a working LibGAP.jl, it is a bit annoying to work on this)

# lists
getindex(x::GapObj, i::Int) = GAP.GAPFuncs.ELM_LIST(x, to_gap(i))
setindex!(x::GapObj, v, i::Int) = GAP.GAPFuncs.ASS_LIST(x, to_gap(i), to_gap(v))

# matrix
getindex(x::GapObj, i::Int, j::Int) = GAP.GAPFuncs.ELM_LIST(x, to_gap(i), to_gap(j))
setindex!(x::GapObj, v, i::Int, j::Int) = GAP.GAPFuncs.ASS_LIST(x, to_gap(i), to_gap(j), to_gap(v))

# records
RNamObj(f::Symbol) = GAP.GAPFuncs.RNamObj(to_gap(string(f)))
getproperty(x::GapObj, f::Symbol) = GAP.GAPFuncs.ELM_REC(x, RNamObj(f))
setproperty!(x::GapObj, f::Symbol, v) = GAP.GAPFuncs.ASS_REC(x, RNamObj(f), to_gap(v))

[ThomasBreuer]

Generic Julia methods would make sense also for append!, push!, show (here we get again the request for a working ViewString like feature in GAP),
and also for ==, <, +, -, *, /, ^, mod.

[fingolfin]

I think @sebasguts added the former, but the latter is still missing (as I just discovered). Also, none of this is being tested right now.

[fingolfin]

Another generic method: string.

And all of these also should apply for GapFFE, too.

[fingolfin]

In addition, the converse would also be nice: I.e. to have methods for \[\], \=, \< etc. in GAP for Julia objects.

[fingolfin]

I just noticed that JuliaExperimental provides the latter (GAP helpers to map + to Julia's +, etc.) in its arith.gi file. Now I wonder if that shouldn't be moved to JuliaInterface?

[sebasguts]

Either that, yes, or add those arithmetics to the GAP dispatch tables using julia's @cfunction.

[fingolfin]

We moved the GAP wrappers for Julia arithmetic to JuliaInterface in PR #132. So far it is purely on the GAP level. We could of course looking into also doing it via the GAP dispatch tables, though it's not completely clear to me that this would be worth it.