calculator.fourth

: add ( n1 n2 -- n3 )  + ;
: subtract ( n1 n2 -- n3 )  - ;
: multiply ( n1 n2 -- n3 )  * ;
: divide ( n1 n2 -- n3 )  / ;

: calculate ( -- )
    ." Enter first number: " 0 .  ( Prompt for first number )
    accept  ( Read input )
    >number drop  ( Convert string to number, drop the remainder )
    dup >r  ( Duplicate first number and store it on the return stack )

    ." Enter operation (+, -, *, /): " 0 .  ( Prompt for operation )
    accept  ( Read input )
    >number drop  ( Convert string to number, drop the remainder )
    r>  ( Retrieve first number from the return stack )
    dup >r  ( Duplicate first number and store it on the return stack )

    ." Enter second number: " 0 .  ( Prompt for second number )
    accept  ( Read input )
    >number drop  ( Convert string to number, drop the remainder )
    r>  ( Retrieve first number from the return stack )

    case
        '+' of r@ r> add . endof
        '-' of r@ r> subtract . endof
        '*' of r@ r> multiply . endof
        '/' of r@ r> divide . endof
        drop ." Error: Unsupported operation" cr
    endcase
;

: main ( -- )
    ." Simple Forth Calculator" cr
    begin
        calculate
        ." Do you want to perform another calculation? (y/n): " 0 . 
        accept 
        'y' = if 
            cr 
        else 
            ." Goodbye!" cr 
            exit 
        then
    again
;

main