When you write an algorithm, you never just guess. Work it out carefully, and check that it works. Obviously, that requires a lot of detailed thought. Unfortunately, until you have a great deal of experience, you can find yourself lost in the details. But there are some checks that are easy to make, just to ensure that you have not made a silly blunder.
Does a function make use of its argument(s)? If there is an argument called x, and you never even mention x while computing the answer, something is wrong. (When you define a function by cases, sometimes some of the cases only use some of the arguments. But every argument should be used in at least one case.)
Does a function make use of variables that do not exist? If so, something is wrong. For example, if your function makes use of something called x, but x is not an argument and is not defined using Let, then there is a problem.
If a function works by using commands, has it defined all variables that are required by the result? For example, suppose that you see a function definition
Define
f(x) = y |
...
%Define
and in the ... part you fail to say what y is. Something
is wrong.
Make sure that you have not used the same name for two different things. In particular, be sure that you have not created a variable whose name is the same as the name of an argument. You should never see something like this.
Define
f(x) = y |
Let x = ...
...
%Define
[solve] What is wrong with the following function definition?
Define
hop(x,y) = w |
Let x = 1.0.
Let y = 2.0.
Let answer = x + y + 1.
%Define
[solve] What is wrong with the following function definition?
Define
f(w) = q |
Let q = x + y.
%Define
It is worth the time to do a quick check to see that a function definition passes a few sanity checks. If it doesn't, it needs to be fixed.
You can change the value of a variable using Relet.
In a given context, a given variable always has to have the same type.
It is a good idea to do a careful hand simulation, crossing out the old value of a variable when its value is changed.