I'm trying to write a GHC plugin. The purpose of the plugin is to provide Haskell bindings to Herbie. Herbie (https://github.com/uwplse/herbie) is a program that takes a mathematical statement as input, and gives you a numerically stable formula to compute it as output. The plugin is supposed to automate this process for Haskell programs. I can convert the core expressions into a format for Herbie just fine. Where I'm having trouble is converting the output from Herbie back into core. Given a string that represents a numeric operator (e.g. "log" or "+"), I can get that converted into a Name that matches the Name of the version of that operator in scope at the location. But in order to create an Expr, I need to convert the Name into a Var. All the functions that I can find for this (e.g. mkGlobalVar) also require the type of the variable. But I can't find a way to figure out the Type given a Name. How can I do this?