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-expressions, I, ask three question about it: (null? I), (atom? (car I)), and else.
<2015-09-02 Wed 18:37>
Use cons to build lists.
<2015-09-02 Wed 18:39>
When building a list, describe the first typical element, and then cons it onto the natural recursion.
<2015-09-02 Wed 18:39>
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-expressions, I, use (car I) and (cdr I) if neither (null? I) nor (atom? (car I)) 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?.
<2015-09-02 Wed 18:42>
When building a value with + ,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 x, 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 0 for the value of the terminating line.
<2015-09-02 Wed 18:43>
Simplify only after the function is correct.
<2015-09-02 Wed 18:45>
Recur on the subparts that are of the same nature:
- On the sublists of a list.
- On the subexpressions of an arithmetic expression.
<2015-09-02 Wed 18:46>
Use help functions to abstract from representations.
<2015-09-02 Wed 18:47>
Abstract common patterns with a new function.
<2015-09-02 Wed 18:49>
Build functions to collect more than one value at a time.
<2015-09-02 Wed 18:49>