(define Letrec
    (lambda (expr)
      (match expr
        [(letrec ([,lhs* ,[Lambda -> code*]] ...) (entry-point ,label))
         (let ([code* (apply append (map cons lhs* code*))])
           `(code
              (jump (label ,label))
              ,code* ...))]
        [,expr (error who "invalid Letrec ~s" expr)])))