- The calculator has a stack that can contain real numbers.
- The calculator waits for user input and expects to receive strings containing whitespace separated lists of numbers and opera tors.
- Numbers are pushed on to the stack. Operators operate on numbers that are on the stack.
- Available operators are +, -, *, /, sqrt, undo, clear
- Operators pop their parameters off the stack, and push their results back onto the stack.
- The 'clear' operator removes all items from the stack.
- The 'undo' operator undoes the previous operation. "undo undo" will undo the previo us two operations.
- sqrt performs a square root on the top item from the stack
- The '+', '-', '*', '/' operators perform addition, subtraction, multiplication and division respectively on the top two items from the stack.
- After processing an input string, the calculator displays the current contents of the stack as a space-separated list.
- Numbers should be stored on the stack to at least 15 decimal places of precision, but displayed to 10 decimal places (or less if it causes no loss of precision).
- All numbers should be formatted as plain decimal strings (ie. no engineering formatting).
- If an operator cannot find a sufficient number of parameters on the stack, a warning is displayed:
operator (position: ): insufficient parameters
- After displaying the warning, all further processing of the string terminates and the current state of the stack is displayed.