Lean.Compiler.LCNF.Decl Lean.Compiler.LCNF.Purity.pure →
  (Lean.Compiler.LCNF.LetDecl Lean.Compiler.LCNF.Purity.pure → Lean.FVarIdSet → Lean.Compiler.LCNF.CompilerM Bool) →
    Lean.Compiler.LCNF.CompilerM (Lean.Compiler.LCNF.Decl Lean.Compiler.LCNF.Purity.pure)