This manual gives many examples showing the evaluation of expressions. The examples have a common format that shows the expression being evaluated on the left hand side, an “arrow” in the middle, and the value of the expression written on the right. For example:
(+ 1 2) => 3
Sometimes the arrow and value will be moved under the expression, due to lack of space. Occasionally we will not care what the value is, in which case both the arrow and the value are omitted.
If an example shows an evaluation that results in an error, an error message is shown, prefaced by `error-->':
(+ 1 'foo) error--> Illegal datum
An example that shows printed output marks it with `-|':
(begin (write 'foo) 'bar) -| foo => bar
When this manual indicates that the value returned by some expression is unspecified, it means that the expression will evaluate to some object without signalling an error, but that programs should not depend on the value in any way.