Complete the reverse polish fractions calculator.

Use a vector of fractions for the stack.

Required operators + - * / ^

print only final result of each expression.

print results as fraction and equivalent decimal, lots of precision.

include variables: vector of names and vector of values.

-> can be anywhere in expression.

make it interactive:
  user types reverse polish formula
  program prints the result
  repeat.

The user is required to separate all parts of the formula with space(s).
But if you want, you can remove that requirement, it is only a little
bit more effort. Two fractions will still need separation, but operators
could live without it.

Your program will need to read a whole line in one go, and use something
like (but much simpler than) the reader for fractions to split the line
into its (used to be) space separated substrings. I have added a reminder
of how to read a whole line at once to the end of the notes for 28th
January. Do it that way.