revised report on scheme which introduced LET to scheme at the time still didn't guarantee left-to-right order of evaluation, "the argument forms can in princip

revised report on scheme which introduced LET to scheme at the time still didn't guarantee left-to-right order of evaluation, "the argument forms can in principle be evaluated in any order. this is unlike the usual LISP left-to-right order". so when introducing LET, which is defined in terms of LAMBDA, the report reiterates that order of evaluation is not guaranteed.