#### Implementation hints

Every RPN expression may be viewed as a sequence of tokens each having both a type and a content. Consider the following expression -1.34 0.34 + sqrt consisting of four tokens:

Type: Double | Type: Double| Type: Binary plus | Type: square Function
|             |       operator    |       root
Value: -1.34 | Value: 0.34 | Value: +          | value: sqrt

The following scanner application utilizes pattern matching for decomposing expressions like -1.34 0.34 + sqrt into a token sequence:

The current example expression -1.34 0.34 + sqrt results in:

We provide error handling capabilities dealing with erroneous input ❶:

Bogus input like 2.1 -3.4 pbck will now be detected as such:

A token sequence may then be evaluated using the postfix evaluation algorithm (Read it!).