implementation: continued pre-processing section; added cache to ExpressionProcessing.jl to improve performance

package/src/ExpressionProcessing.jl

@@ -17,12 +17,16 @@ struct ExpressionElement
 end
 
 const PostfixType = Vector{ExpressionElement}
-
+const cache = Dict{Expr, PostfixType}()
 "
 Converts a julia expression to its postfix notation.
 NOTE: All 64-Bit values will be converted to 32-Bit. Be aware of the lost precision
 "
 function expr_to_postfix(expr::Expr)::PostfixType
+	if haskey(cache, expr)
+		return cache[expr]
+	end
+
 	postfix = PostfixType()
 	@inbounds operator = get_operator(expr.args[1])
 
@@ -40,7 +44,8 @@ function expr_to_postfix(expr::Expr)::PostfixType
 			push!(postfix, exprElement)
 		end
 
-		# only add operator if at least 2 values are added. For the case where another expression is added first, we check if we are at the first iteration or not ( j != 2)
+		# only add operator if at least 2 values are added. Needed because e.g. multiple consecutive additions are one subtree with one operator, but multiple operators need to be added to the postfix notation. 
+		# For the case where another expression has already been added, we check if we are at the first iteration or not ( j != 2)
 		if length(postfix) >= 2 && j != 2
 			exprElement = convert_to_ExpressionElement(operator)
 			push!(postfix, exprElement)