Consider this paragraph from 'The Elements of Programming':
This uses the special form if, a restricted type of conditional that can be used when there are precisely two cases in the case analysis. The general form of an if expression is
(if ⟨predicate⟩ ⟨consequent⟩ ⟨alternative⟩)
To evaluate an if expression, the interpreter starts by evaluating the ⟨predicate⟩ part of the expression. If the ⟨predicate⟩ evaluates to a true value, the interpreter then evaluates the ⟨consequent⟩ and returns its value. Otherwise it evaluates the ⟨alternative⟩ and returns its value.
I understand that "precisely" means "exactly". But I got confused when it is asociated with the phrase "can be used".
What does the phrase "can be used when there are precisely two cases" mean exactly? Could it be:
- I can only use this conditional only if I have two cases, nothing less?
- I can use this conditional if I have two cases, but I can still use it even though I only have one case?