Interactive code:
https://replit.com/@alexandresouto/rpncalc#main.cr

A Reverse Polish Notation Calculator, with expression/macro functionality.

All Operators:

Math (1 operator): sq sqrt [ln|log] [neg|opo] inv floor ceil
Math (2 operators): [+] [-] [*] [/] [**|pow] [%|mod] log_
Math (N operators): sum mult max min
Random Numbers: 'rand' returns a random float 0~1, 'randi' returns a random integer 0~(N-1)
Stack Handling: dup cpy cpyn cpyto pop del deln [clr|clear] [swp|swap]
Qtty of numbers in the line until the comma: [,]
Stack size: [.|qtt|qtty]
Create Expression: { <w1> <w2> <w3> ... } <name>
List Expressions: expr or expri(for indexes)
Delete Expression: <N> delxpr
Repeat <w1> N times: repeat_<w1>
Execute <w1> or <w2> conditionally: doif_<w1>_<w2>
Set a variable <w1>: set_<w1> Example: 5 set_x
Help: [help|cmds]
Exit: [exit|out]

There are two programming Operators: repeat_value1 and doif_value1_value2

Values can be Numeric Values, Operators, or Expressions

repeat_value1 consumes the last value as a quantity N
And apply value1 N times in the stack

doif_value1_value2 consumes the last value as a condition
Any positive number is considered true, otherwise it is considered false
if true apply value1 on the stack, if false apply value2 on the stack
_value2 is optional
_value1 can be omited with a doif__value2

Definining expressions example:

Type "{ 2 * } double" to define the "double" expression
With the stack "[5]", typing "double" results in "[10]"
With the stack "[10]", typing "8 + double" results in "[36]"