Loop only through vars to infer

src/acset.jl

@@ -363,12 +363,31 @@ function safe_modifytype!(d::SummationDecapode, var_idx::Int, new_type::Symbol)
   return modify
 end
 
+"""
+    filterfor_forms(types::AbstractVector{Symbol})
+
+Return any form type symbols.
+"""
 function filterfor_forms(types::AbstractVector{Symbol})
   conditions = x -> x != :Literal && x != :Constant && x != :Parameter && x != :infer
   filter(conditions, types)
 end
 
-# ! Warning: This is changing types to :Constant when they weren't originally.
+"""
+    filterfor_forms(types::AbstractVector{Symbol})
+
+Return the indices of any variables with form types.
+"""
+function filterfor_forms(d::SummationDecapode, type_idxs::AbstractVector{Int})
+  conditions = x -> d[x, :type] != :Literal &&
+    d[x, :type] != :Constant &&
+    d[x, :type] != :Parameter &&
+    d[x, :type] != :infer
+
+  filter(conditions, type_idxs)
+end
+
+
 function infer_summands_and_summations!(d::SummationDecapode)
   # Note that we are not doing any type checking here for users!
   # i.e. We are not checking the underlying types of Constant or Parameter
@@ -377,9 +396,9 @@ function infer_summands_and_summations!(d::SummationDecapode)
   for Σ_idx in parts(d, :Σ)
     summands = d[incident(d, Σ_idx, :summation), :summand]
     sum = d[Σ_idx, :sum]
-    idxs = [summands; sum]
+    idxs = filterfor_forms(d, [summands; sum])
 
-    forms = unique(filterfor_forms(d[idxs, :type]))
+    forms = unique(d[idxs, :type])
 
     form = @match length(forms) begin
       0 => continue # We need not infer, We can not infer