; (tc_fun, fun_sigma) <- tcInferAppHead fun

        ; code_orig <- getSrcCodeOrigin

        ; let fun_orig = srcCodeOriginCtOrigin rn_expr code_orig

        ; tc_args <- tcValArgs do_ql (rn_fun, generatedSrcSpan) inst_args

        ; let tc_expr = rebuildHsApps (tc_fun, fun_ctxt) tc_args

        ; return (tc_expr, app_res_sigma) }

        -- Setp 3.2 Set the correct origin to blame for the error message

        -- What should be the origin for this function call?

        -- source code origin stored in the lclEnv.

        -- See Note [Error contexts in generated code]

        -- See Note [Error Context Stack]

        ; code_orig <- getSrcCodeOrigin

        ; traceTc "tcApp:inferAppHead" $

          vcat [ text "tc_fun:" <+> ppr tc_fun

               , text "fun_origin" <+> ppr fun_orig

               , text "do_ql:" <+> ppr do_ql]

        ; (inst_args, app_res_rho)

          -- See (TCAPP1) and (TCAPP2) in

          -- Note [tcApp: typechecking applications]

                     --           always return a rho-type (but not a deep-rho type)

                     -- Generally speaking we pass in True; in Fig 5 of the paper

                     --    |-inst returns a rho-type

           -> TcSigmaType -> [HsExprArg 'TcpRn]

           -> TcM ( [HsExprArg 'TcpInst]

                  , TcSigmaType )   -- Does not instantiate trailing invisible foralls

 -- This crucial function implements the |-inst judgement in Fig 4, plus the

 -- modification in Fig 5, of the QL paper:

 -- "A quick look at impredicativity" (ICFP'20).

   = do { traceTc "tcInstFun" (vcat [ text "origin" <+> ppr fun_orig

                                    , text "tc_fun" <+> ppr tc_fun

                                    , text "fun_sigma" <+> ppr fun_sigma

        ; do_ql <- wantQuickLook rn_fun

        ; ((inst_args, app_res_rho), wanted)

              <- captureConstraints $

                 -- We must capture type-class and equality constraints here, but

                 -- not equality constraints.  See (QLA6) in Note [Quick Look at

                 -- value arguments]

 --

 -- See Note [tcApp: typechecking applications] in GHC.Tc.Gen.App

 tcInferAppHead (fun,fun_lspan)

     do { mb_tc_fun <- tcInferAppHead_maybe fun

        ; case mb_tc_fun of

             Just (fun', fun_sigma) -> return (fun', fun_sigma)

     case fun of

       HsVar _ nm                  -> Just <$> tcInferId nm

       XExpr (HsRecSelRn f)        -> Just <$> tcInferRecSelId f

                                               -- We do not want to instantiate c.f. T19167

       ExprWithTySig _ e hs_ty     -> Just <$> tcExprWithSig e hs_ty

       HsOverLit _ lit             -> Just <$> tcInferOverLit lit

       _                           -> return Nothing

                  return b

 rebindable6.hs:112:17: error: [GHC-39999]

       prevents the constraint ‘(HasReturn (b -> t1))’ from being solved.

       (maybe you haven't applied a function to enough arguments?)

       Relevant bindings include