Ruby arithmetic calculator

A basic arithmetic calculator implemented in Ruby

Consists of:

Lexer (converts input string to array of tokens)
Parser (converts array of tokens to RPN)
Evaluator (evaluates RPN expression)

Supports following arithmetic operations:

+ (addition)
- (subtraction)
/ (division)
* (multiplication)
^ (exponentiation)
log (taking the logarithm)

Usage:

ruby app.rb [expression]

Example:

ruby app.rb "log 100 10 * ((4 - 7) ^ (3 + 1) / 4)"