[#153] Only do transformation when the letrec body is a lambda
[#153] Only do transformation when the letrec body is a lambda

wxzh/fcore,bixuanzju/fcore,zhiyuanshi/fcore,bixuanzju/fcore,wxzh/fcore,hkuplg/fcore,wxzh/fcore,xnning/fcore,zhiyuanshi/fcore,zhiyuanshi/fcore,xnning/fcore,xnning/fcore,hkuplg/fcore,hkuplg/fcore,bixuanzju/fcore