The Five Rules
The Law of Car: the primitive car is defined only for non-empty lists
The Law of Cdr: the primitive cdr is defined only for non-empty lists.The cdr of any non-empty list is always another list.
The Law of Cons: The primitive cons takes two arguments. The second argument to cons must be a list. The result is a list.
The Law of Null?: the primitive null? is defined only for lists.
The Law of Eq?: the primitive eq? takes two arguments. Both of them must be non-numeric atoms.
<cons> takes two arguments: the first one is any S-expression; the second one is any list.
<atom?>take a argument. The argument can be any S-expression. (查看原文)
The First Commandment: Always ask null? as the first question in expressing any function.
The Second Commandment: Use cons to build lists.
The Third Commandment: When building a list, describe the first typical element,and then cons is onto the natural recursion.
The Fourth Commandment: Always change at least one argument while recurring. It must be changed to be closer to termination. The changing argument must be tested int the termination condition; when using cdr, test termination with null? (查看原文)
First: When recurring on a list of atomes, lat, ask two questions about it: (null? lat) and else. When recurring on a number, n, ask two questions about it: (zero? n) and else.
Second: When building a value with +,always use 0 fro the value of the terminating line,
for adding 0 does not change the value of an addition.
When building a value with *,always use 1 for the value of the terminating line, for multiplying by 1 does not change the value of a multiplication.
When building a value with cons,alway consider null-list for the value of the terminating line. (查看原文)
When recurring on a list of S-expressions, l, ask three question about it: (null? l), (atom? (car l)), and else.
Simplify only after the function correct. (查看原文)
