program using Scheme that evaluates a postfix expression

Question

I want to convert a postfix expression using scheme The expression will be given to the interpreter as a list of operands and operators such as display( postfix(30 8 7 + / 3 4 - *) ) This example should return -2 as answer.

Answer 1

Here's pseudo-code:

• Initialize stack to empty list
• For each element e in the expression:
  • if e is a number, push it onto the stack
  • otherwise, call the function corresponding to the operator (you can use an association list or cond to find this), passing the stack as the parameter
    - The function pops the needed arguments off the stack
    - It calculates the result
    - It pushes the result onto the stack
    - It returns the updated stack, which the main loop assigns back to the stack variable
• At the end, print the top element of the stack