Hi ghc-devs, I've been trying to implementing a function with the signature: elaborateExpr :: GhcMonad m => String -> m CoreExpr It should take a string of the form: "\x y -> x <> y :: Semigroup a => a -> a -> a" and give back a core expression with the dictionaries filled in: \ ($dSem :: Semigroup a) (x :: a) (y :: a) -> (<>) $dSem x y The goal is to use the function to add elaboration support for liquidhaskell. I looked into the implementation of exprType https://hackage.haskell.org/package/ghc-8.6.5/docs/CoreUtils.html#v:exprType and defined my own elaborateExpr https://github.com/yiyunliu/ghc-elaboration-test/blob/30b3307469df15789cf1a3... similarly by calling desugarExpr https://hackage.haskell.org/package/ghc-8.6.5/docs/Desugar.html#v:deSugarExp... on the expression (which has type LHsExpr GhcTcId) returned by tcInferSigma. GhcTcId is a synonym of GhcTc so the program I wrote typechecks, but it's definitely not right. The elaborateExpr function I defined would return something even when the expression doesn't typecheck, or occasionally give a runtime exception: ghc-elaboration-test: panic! (the 'impossible' happened) (GHC version 8.6.5 for x86_64-unknown-linux): dsEvBinds I must have broken some invariants somehow. What is the correct way of defining such a function (takes a string and returns a CoreExpr)? It appears to me that I should convert LHsExpr GhcPs into LHsExpr GhcTc first before calling deSugarExpr, but I don't know how. Thank you, - Yiyun