support gap_to_julia(::AbstractVector) (#989)

* support `gap_to_julia(::BitVector)`

This had been claimed already before the change,
but it was not tested.

* adjust the conversion of ranges

After generalizing the three-argument method of `julia_to_gap`
from `Vector` to `AbstractVector`,
the default method that discards the last two arguments is no longer
applicable to `AbstractRange{<:Integer}`,
hence the special one-argument method does not get called.

For the moment, install a three-argument method for `AbstractRange{<:Integer}`.

(And add tests that check whether we really get a GAP `IsRange` object in the end.)

* polish

- do not show `C_NULL` but just its type (since printing has changed in Julia)
- fix a typo

src/julia_to_gap.jl

@@ -116,7 +116,7 @@ julia_to_gap(obj::Any, recursion_dict::IdDict{Any,Any}; recursive::Bool = true)
 
 ## Arrays (including BitVector)
 function julia_to_gap(
-    obj::Vector{T},
+    obj::AbstractVector{T},
     recursion_dict::IdDict{Any,Any} = IdDict();
     recursive::Bool = false,
 ) where {T}
@@ -172,12 +172,20 @@ function julia_to_gap(
 end
 
 ## Ranges
-function julia_to_gap(r::AbstractRange{<:Integer})
+function julia_to_gap(r::AbstractRange{<:Integer}, recursive::Bool = false)
     res = NewRange(length(r), first(r), step(r))
     Wrappers.IsRange(res) || throw(ConversionError(r, GapObj))
     return res
 end
 
+function julia_to_gap(
+    r::AbstractRange{<:Integer},
+    recursion_dict::IdDict{Any,Any};
+    recursive::Bool = false)
+
+    return julia_to_gap(r)
+end
+
 ## Dictionaries
 function julia_to_gap(
     obj::Dict{T,S},

test/conversion.jl

@@ -387,6 +387,11 @@ end
     y = GAP.julia_to_gap([true, false])
     @test y == x
     @test GAP.gap_to_julia(GAP.Globals.TNAM_OBJ(y)) == "list (boolean)"
+
+    v = BitVector([true, false])
+    gap_v = GAP.julia_to_gap(v)
+    @test gap_v == x
+    @test GAP.gap_to_julia(GAP.Globals.TNAM_OBJ(gap_v)) == "list (boolean)"
   end
 
   @testset "Tuples" begin
@@ -409,6 +414,11 @@ end
     r = GAP.evalstr("[ 1, 4 .. 10 ]")
     @test GAP.julia_to_gap(1:3:10) == r
     @test_throws GAP.ConversionError GAP.julia_to_gap(1:2^62)
+
+    r = GAP.julia_to_gap(1:2:11, IdDict(), recursive = false)
+    @test GAP.gap_to_julia(GAP.Globals.TNAM_OBJ(r)) == "list (range,ssort)"
+    r = GAP.Obj(1:10)
+    @test GAP.gap_to_julia(GAP.Globals.TNAM_OBJ(r)) == "list (range,ssort)"
   end
 
   @testset "Dictionaries" begin