From 1b14b5910cc30967346f46d0541a31b8a8d4a929 Mon Sep 17 00:00:00 2001
From: Max Horn <max@quendi.de>
Date: Wed, 5 Apr 2023 22:47:05 +0200
Subject: [PATCH] Allow iterating over Julia objects from within GAP

---
 CHANGES.md                         |  4 ++++
 pkg/JuliaInterface/gap/adapter.gi  | 38 ++++++++++++++++++++++++++++++
 pkg/JuliaInterface/tst/adapter.tst |  9 +++++++
 pkg/JuliaInterface/tst/convert.tst |  7 ++++++
 4 files changed, 58 insertions(+)

diff --git a/CHANGES.md b/CHANGES.md
index 49ac1ba5..893900d9 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,9 @@
 # Changes in GAP.jl
 
+## Version 0.9.5-DEV (released YYYY-MM-DD)
+
+- Allow iterating over Julia objects from within GAP
+
 ## Version 0.9.4 (released 2023-03-04)
 
 - Tweak @gapattribute to not require `import GAP: @gapwrap`
diff --git a/pkg/JuliaInterface/gap/adapter.gi b/pkg/JuliaInterface/gap/adapter.gi
index a8f53dc2..69022ca1 100644
--- a/pkg/JuliaInterface/gap/adapter.gi
+++ b/pkg/JuliaInterface/gap/adapter.gi
@@ -84,6 +84,44 @@ InstallOtherMethod( \.\:\=,
     end );
 
 
+#############################################################################
+##
+##  Iterating over Julia objects
+##
+BindGlobal("NextIterator_Julia", function(it)
+  local res;
+  res := it!.state[1];
+  it!.state := Julia.iterate(it!.obj, it!.state[2]);
+  return res;
+end);
+
+BindGlobal("IsDoneIterator_Julia", function(it)
+  return Julia.isnothing(it!.state);
+end);
+
+BindGlobal("ShallowCopy_Julia", function(it)
+  return rec(NextIterator := it!.NextIterator,
+    IsDoneIterator := it!.IsDoneIterator,
+    ShallowCopy := it!.ShallowCopy,
+    state := Julia.Base.deepcopy(it!.state),
+    obj := it!.obj,
+    );
+end);
+
+InstallOtherMethod( Iterator,
+    "for a Julia object",
+    [ IsJuliaObject ],
+function(obj)
+  return IteratorByFunctions(rec(
+    NextIterator := NextIterator_Julia,
+    IsDoneIterator := IsDoneIterator_Julia,
+    ShallowCopy := ShallowCopy_Julia,
+    state := Julia.iterate(obj),
+    obj := obj,
+  ));
+end);
+
+
 #############################################################################
 ##
 ##  Create random numbers via Julia random number generators.
diff --git a/pkg/JuliaInterface/tst/adapter.tst b/pkg/JuliaInterface/tst/adapter.tst
index c36d368a..919c8d9e 100644
--- a/pkg/JuliaInterface/tst/adapter.tst
+++ b/pkg/JuliaInterface/tst/adapter.tst
@@ -89,6 +89,10 @@ gap> TestBinOp({a,b} -> a = b);
 #
 gap> l := GAPToJulia([1, 2, 3]);
 <Julia: Any[1, 2, 3]>
+gap> for i in l do Display(i); od;
+1
+2
+3
 gap> l[1];
 1
 gap> l[2] := false;
@@ -101,6 +105,11 @@ gap> l;
 #
 gap> m:=JuliaEvalString("[1 2; 3 4]");
 <Julia: [1 2; 3 4]>
+gap> for i in m do Display(i); od;
+1
+3
+2
+4
 gap> m[3];
 2
 gap> m[1,2];
diff --git a/pkg/JuliaInterface/tst/convert.tst b/pkg/JuliaInterface/tst/convert.tst
index d2a8500a..2400cc73 100644
--- a/pkg/JuliaInterface/tst/convert.tst
+++ b/pkg/JuliaInterface/tst/convert.tst
@@ -222,5 +222,12 @@ gap> dict:= GAPToJulia( rec( juliafunc:= Julia.Base.map,
 gap> JuliaToGAP( IsRecord, dict );
 rec( juliafunc := <Julia: map> )
 
+# iterating over dict gives key-value pairs
+gap> dict:= GAPToJulia( rec( a := 1, b := 2 ) );
+<Julia: Dict{Symbol, Any}(:a => 1, :b => 2)>
+gap> for i in dict do Display(i); od;
+Pair{Symbol, Any}(:a, 1)
+Pair{Symbol, Any}(:b, 2)
+
 ##
 gap> STOP_TEST( "convert.tst", 1 );