《The Little Schemer》 FP编程、lisp入门必备
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. Each must be a non-numeric atom.
The First Commandment
When recurring on a list of atoms, 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. When recurring on a list of S-exp, l, ask three question about it: (null? l), (atom? (car l)), and else.
The Second Commandment
Use cons to build lists.
The Third Commandment
When building a list, describe the first typical element, and then cons it onto the natural recursion.
The Fourth Commandment
Always change at least one argument while recurring. When recurring on a list of atoms, lat, use (cdr lat). When recurring on a number, n, use (sub1 n). And when recurring on a list of S-exp, l, use (car l) and (cdr l) if neither (null? l) noe (atom? (car l)) are true. It must be changed to be closer to termination. The changing argument must be tested in the termination condition: when using cdr, test termination with null? and when using sub1, test termination with zero?
The Fifth Commandment
When building a value with o+, always use 0 for 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, always consider () for the value of the terminating line.
The Sixth Commandment
Simplify only after the function is correct.
The Seventh Commandment
Recur on the subparts that are of the same nature: * On the sublists of a list. * On the subexpressions of an arithmetic expression.
The Eighth Commandment
Use help function to abstract from representations.
The Ninth Commandment
Abstract common patterns with a new function