问题问题:
Define a LISP function SCORE->GRADE which takes a single argument, s, and returns a symbol according to the following scheme:
s ? 90 A 73 ? s < 77 C+
87 ? s < 90 A– 70 ? s < 73 C
83 ? s < 87 B+ 60 ? s < 70 D
80 ? s < 83 B s < 60 F
77 ? s < 80 B–
If the argument s is not a number then …