Move out vertex mapping from to_einexpr to tensor_inds_to_vertex

ext/ITensorNetworksEinExprsExt/src/ITensorNetworksEinExprsExt.jl

@@ -10,30 +10,37 @@ using ITensorNetworks:
   contraction_sequence
 using EinExprs: EinExprs, EinExpr, einexpr, SizedEinExpr
 
-function to_einexpr(tn::ITensorNetwork)
+function to_einexpr(tn::AbstractITensorNetwork)
   IndexType = Any
-  VertexType = vertextype(tn)
 
   tensor_exprs = EinExpr{IndexType}[]
-  tensor_inds_to_vertex = Dict{Set{IndexType},VertexType}()
   inds_dims = Dict{IndexType,Int}()
 
   for v in vertices(tn)
     tensor_v = tn[v]
     inds_v = collect(inds(tensor_v))
     push!(tensor_exprs, EinExpr{IndexType}(; head=inds_v))
-    tensor_inds_to_vertex[Set(inds_v)] = key
     merge!(inds_dims, Dict(inds_v .=> size(tensor_v)))
   end
 
   externalinds_tn = collect(externalinds(tn))
-  expr = SizedEinExpr(sum(tensor_exprs; skip=externalinds_tn), inds_dims)
+  return SizedEinExpr(sum(tensor_exprs; skip=externalinds_tn), inds_dims)
+end
+
+function tensor_inds_to_vertex(tn::AbstractITensorNetwork)
+  mapping = Dict{Set{IndexType},VertexType}()
+
+  for v in vertices(tn)
+    tensor_v = tn[v]
+    inds_v = collect(inds(tensor_v))
+    mapping[Set(inds_v)] = v
+  end
 
-  return expr, tensor_inds_to_vertex
+  return mapping
 end
 
 function EinExprs.einexpr(tn::ITensorNetwork; optimizer::EinExprs.Optimizer)
-  expr, _ = to_einexpr(tn)
+  expr = to_einexpr(tn)
   return einexpr(optimizer, expr)
 end
 
@@ -46,8 +53,8 @@ end
 function ITensorNetworks.contraction_sequence(
   ::Algorithm"einexpr", tn::ITensorNetwork{T}; optimizer=EinExprs.Exhaustive()
 )
-  expr, tensor_inds_to_vertex = to_einexpr(tn)
-  return to_contraction_sequence(expr, tensor_inds_to_vertex)
+  expr = einexpr(tn; optimizer)
+  return to_contraction_sequence(expr, tensor_inds_to_vertex(tn))
 end
 
 function to_contraction_sequence(expr, tensor_inds_to_vertex)