a few improvements

(motivated mainly by gap-packages/PackageManager/pull/134
and the issues mentioned there)

- support keyword arguments in `CallJuliaFunctionWithCatch`

- do not use the deprecated and undocumented `Core._apply`

- update the initializations in `init_packagemanager`:
  Replacing `PKGMAN_DownloadURL` is no longer needed,
  replacing `PKGMAN_RemoveDir` was in a wrong place.

- start better documentation of Julia syntax features

pkg/JuliaInterface/gap/JuliaInterface.gd

@@ -237,6 +237,24 @@ DeclareGlobalFunction( "JuliaImportPackage" );
 
 
 #! @Section Access to &Julia; objects
+#!  Not all &Julia; syntax features are supported in ⪆.
+#!  For important ones, the interface provides ⪆ functions or
+#!  helper functions written in &Julia; to use them in ⪆.
+#!  For example, <Ref Func="CallJuliaFunctionWithCatch"/> allows one to use
+#!  &Julia;'s try/catch statements.
+#!
+#!  Here is a selection of other workarounds for &Julia; syntax features.
+#!  <List>
+#!  <Item>
+#!    &Julia;'s <C>RefValue</C> objects can be handled as follows.
+#!    If <C>x</C> is such an object then its value can be fetched with
+#!    <C>Julia.GAP.getindex( x )</C>,
+#!    a value <C>v</C> of the right type can be set with
+#!    <C>Julia.GAP.setindex( x, v )</C>,
+#!    and one can check with <C>Julia.GAP.isassigned( x )</C>
+#!    whether <C>x</C> has a value.
+#!  </Item>
+#!  </List>
 
 ## Internal
 BindGlobal( "_JuliaFunctions", rec( ) );
@@ -299,6 +317,19 @@ DeclareGlobalFunction( "JuliaFunction" );
 #! gap> Julia.Main.x;
 #! 1
 #! @EndExampleSession
+#!
+#!  Note that not all &Julia; variables are directly visible in its
+#!  <C>Main</C> module.
+#!  For example, &Julia; variables from the interface to &GAP; are defined
+#!  in the &Julia; module <C>GAP</C> or its submodules.
+#!  It is safe to access this module as <C>Julia.GAP</C>.
+#!
+#! @BeginExampleSession
+#! gap> Julia.GAP;
+#! <Julia module GAP>
+#! gap> Julia.GAP.prompt;
+#! <Julia: prompt>
+#! @EndExampleSession
 DeclareGlobalVariable( "Julia" );
 
 #! @Arguments name
@@ -331,11 +362,13 @@ DeclareGlobalFunction( "JuliaModule" );
 #! @EndExampleSession
 DeclareGlobalFunction( "JuliaTypeInfo" );
 
-#! @Arguments juliafunc, arguments
+#! @Arguments juliafunc, arguments[, arec]
 #! @Returns a record.
 #! @Description
 #!  The function calls the &Julia; function <A>juliafunc</A>
-#!  with arguments in the &GAP; list <A>arguments</A>,
+#!  with ordinary arguments in the &GAP; list <A>arguments</A>
+#!  and optionally with keyword arguments given by the component names (keys)
+#!  and values of the &GAP; record <A>arec</A>,
 #!  and returns a record with the components <C>ok</C> and <C>value</C>.
 #!  If no error occurred then <C>ok</C> has the value <K>true</K>,
 #!  and <C>value</C> is the value returned by <A>juliafunc</A>.
@@ -358,6 +391,15 @@ DeclareGlobalFunction( "JuliaTypeInfo" );
 #! false
 #! gap> res.value{ [ 1 .. Position( res.value, '(' )-1 ] };
 #! "LinearAlgebra.SingularException"
+#! gap> fun:= Julia.range;;
+#! gap> CallJuliaFunctionWithCatch( fun, [ 2, 10 ], rec( step:= 2 ) );
+#! rec( ok := true, value := <Julia: 2:2:10> )
+#! gap> res:= CallJuliaFunctionWithCatch( fun, [ 2, 10 ],
+#! >              rec( step:= GAPToJulia( "a" ) ) );;
+#! gap> res.ok;
+#! false
+#! gap> res.value{ [ 1 .. Position( res.value, '(' )-1 ] };
+#! "MethodError"
 #! @EndExampleSession
 DeclareGlobalFunction( "CallJuliaFunctionWithCatch" );
 
@@ -461,19 +503,17 @@ DeclareGlobalFunction( "CallJuliaFunctionWithKeywordArguments" );
 #!  <List>
 #!  <Item>
 #!    <Ref Oper="CallFuncList" BookName="ref"/>,
-#!    delegating to <C>Julia.Core._apply</C>
-#!    (this yields the function call syntax in &GAP;,
+#!    delegating to &Julia;'s <C>func(args...)</C> syntax;
+#!    this yields the function call syntax in &GAP;,
 #!    it is installed also for objects in
 #!    <Ref Filt="IsJuliaWrapper" Label="for IsObject"/>,
 #!  </Item>
 #!  <Item>
 #!    access to and assignment of entries of arrays, via
 #!    <Ref Oper="\[\]" BookName="ref"/>,
 #!    <Ref Oper="\[\]\:\=" BookName="ref"/>,
-#!    <!-- <Ref Oper="MatElm" BookName="ref"/>, and
-#!    <Ref Oper="SetMatElm" BookName="ref"/>, -->
-#!    and the (up to &GAP; 4.11 undocumented) operations <C>MatElm</C> and
-#!    <C>SetMatElm</C>,
+#!    <Ref Oper="MatElm" BookName="ref"/>, and
+#!    <Ref Oper="SetMatElm" BookName="ref"/>,
 #!    delegating to
 #!    <C>Julia.Base.getindex</C> and
 #!    <C>Julia.Base.setindex</C>,
@@ -532,7 +572,6 @@ DeclareGlobalFunction( "CallJuliaFunctionWithKeywordArguments" );
 #! gap> m + m;
 #! <Julia: [2 4; 6 8]>
 #! @EndExampleSession
-#TODO: add the cross-references to MatElm, SetMatElm when they are documented
 
 #! @InsertChunk JuliaHelpInGAP
 

pkg/JuliaInterface/gap/calls.gi

@@ -12,7 +12,7 @@ InstallMethod( CallFuncList,
     [ "IsJuliaObject", "IsList" ],
     function( julia_obj, args )
         args := GAPToJulia( _JL_Vector_Any, args, false );
-        return Julia.Core._apply( julia_obj, args );
+        return Julia.GAP._apply( julia_obj, args );
     end );
 
 InstallMethod( CallFuncList,
@@ -22,14 +22,21 @@ InstallMethod( CallFuncList,
     end );
 
 InstallGlobalFunction( CallJuliaFunctionWithCatch,
-    function( julia_obj, args )
+    function( julia_obj, args, arec... )
     local res;
 
     args := GAPToJulia( _JL_Vector_Any, args, false );
     if IsFunction( julia_obj ) then
       julia_obj:= Julia.GAP.UnwrapJuliaFunc( julia_obj );
     fi;
-    res:= Julia.GAP.call_with_catch( julia_obj, args );
+    if Length( arec ) = 0 then
+      res:= Julia.GAP.call_with_catch( julia_obj, args );
+    elif Length( arec ) = 1 and IsRecord( arec[1] ) then
+      arec := GAPToJulia( _JL_Dict_Any, arec[1], false );
+      res:= Julia.GAP.call_with_catch( julia_obj, args, arec );
+    else
+      Error( "usage: CallJuliaFunctionWithCatch( <julia_obj>, <args>, <arec>" );
+    fi;
     if res[1] then
       return rec( ok:= true, value:= res[2] );
     else

pkg/JuliaInterface/tst/utils.tst

@@ -19,6 +19,8 @@ gap> res.ok;
 false
 gap> StartsWith( res.value, "DomainError" );
 true
+gap> CallJuliaFunctionWithCatch( Julia.Base.sqrt, [ 4 ], rec() );
+rec( ok := true, value := <Julia: 2.0> )
 
 ##
 gap> JuliaEvalString(fail);

src/packages.jl

@@ -9,25 +9,12 @@ const DEFAULT_PKGDIR = Ref{String}()
 const DOWNLOAD_HELPER = Ref{Downloads.Downloader}()
 
 function init_packagemanager()
-#TODO:
-# As soon as PackageManager uses utils' Download function,
-# we need not replace code from PackageManager anymore.
-# (And the function should be renamed.)
-    res = load("PackageManager")
-    @assert res
-
     global DEFAULT_PKGDIR[] = sysinfo["DEFAULT_PKGDIR"]
+    # This is used by `PKGMAN_DownloadURL` in GAP's PackageManager package.
     global DOWNLOAD_HELPER[] = Downloads.Downloader(; grace=0.1)
-
-    # overwrite PKGMAN_DownloadURL
-    replace_global!(:PKGMAN_DownloadURL, function(url)
-      try
-        buffer = Downloads.download(String(url), IOBuffer(), downloader=DOWNLOAD_HELPER[])
-        return GapObj(Dict{Symbol, Any}(:success => true, :result => String(take!(buffer))), recursive=true)
-      catch
-        return GapObj(Dict{Symbol, Any}(:success => false), recursive=true)
-      end
-    end)
+    # We need functions from PackageManager.
+    res = load("PackageManager")
+    @assert res
 
     # Install a method (based on Julia's Downloads package) as the first choice
     # for the `Download` function from GAP's utils package,
@@ -59,15 +46,15 @@ function init_packagemanager()
       # put the new method in the first position
       meths = Globals.Download_Methods
       Wrappers.Add(meths, GapObj(r, recursive=true), 1)
-
-      # monkey patch PackageManager so that we can disable removal of
-      # package directories for debugging purposes
-      orig_PKGMAN_RemoveDir = Globals.PKGMAN_RemoveDir
-      replace_global!(:PKGMAN_RemoveDir, function(dir)
-        Globals.ValueOption(GapObj("debug")) == true && return
-        orig_PKGMAN_RemoveDir(dir)
-      end)
     end
+
+    # monkey patch PackageManager so that we can disable removal of
+    # package directories for debugging purposes
+    orig_PKGMAN_RemoveDir = Globals.PKGMAN_RemoveDir
+    replace_global!(:PKGMAN_RemoveDir, function(dir)
+      Globals.ValueOption(GapObj("debug")) == true && return
+      orig_PKGMAN_RemoveDir(dir)
+    end)
 end
 
 """

src/utils.jl

@@ -15,6 +15,9 @@ function _setglobal(M::Module, name::Symbol, val::Any)
   end
 end
 
+# avoid the deprecated `Core._apply`
+_apply(func, args) = func(args...)
+
 """
     get_symbols_in_module(m::Module) :: Vector{Symbol}
 
@@ -30,32 +33,55 @@ function get_symbols_in_module(m::Module)
 end
 
 """
-    call_with_catch(juliafunc, arguments)
+    call_with_catch(func, args::Vector)
+    call_with_catch(func, args::Vector, kwargs::Dict{Symbol,T}) where T
 
 Return a tuple `(ok, val)`
-where `ok` is either `true`, meaning that calling the function `juliafunc`
-with `arguments` returns the value `val`,
+where `ok` is either `true`, meaning that calling `func`
+with arguments `args` (and optionally with keyword arguments given by
+the keys and values of `kwargs`) returns the value `val`,
 or `false`, meaning that the function call runs into an error;
 in the latter case, `val` is set to the string of the error message.
 
+This function is used on the GAP side.
+
 # Examples
 ```jldoctest
-julia> GAP.call_with_catch(sqrt, 2)
+julia> GAP.call_with_catch(sqrt, [2])
 (true, 1.4142135623730951)
 
-julia> flag, res = GAP.call_with_catch(sqrt, -2);
+julia> flag, res = GAP.call_with_catch(sqrt, [-2]);
 
 julia> flag
 false
 
 julia> startswith(res, "DomainError")
 true
 
+julia> GAP.call_with_catch(range, [2, 10], Dict(:step => 2))
+(true, 2:2:10)
+
+julia> flag, res = GAP.call_with_catch(range, [2, 10], Dict(:step => "a"));
+
+julia> flag
+false
+
+julia> startswith(res, "MethodError")
+true
 ```
 """
-function call_with_catch(juliafunc, arguments)
+function call_with_catch(func, args)
     try
-        res = Core._apply(juliafunc, arguments)
+        res = func(args...)
+        return (true, res)
+    catch e
+        return (false, string(e))
+    end
+end
+
+function call_with_catch(func, args::Vector, kwargs::Dict{Symbol,T}) where T
+    try
+        res = func(args...; [k => kwargs[k] for k in keys(kwargs)]...)
         return (true, res)
     catch e
         return (false, string(e))
@@ -70,7 +96,6 @@ given by the keys and values of `kwargs`.
 
 This function is used on the GAP side, in calls of Julia functions that
 require keyword arguments.
-Note that `jl_call` and `Core._apply` do not support keyword arguments.
 
 # Examples
 ```jldoctest
@@ -79,7 +104,6 @@ julia> range(2, length = 5, step = 2)
 
 julia> GAP.kwarg_wrapper(range, [2], Dict(:length => 5, :step => 2))
 2:2:10
-
 ```
 """
 function kwarg_wrapper(func, args::Vector{T1}, kwargs::Dict{Symbol,T2}) where {T1,T2}