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BrainFuck part 10 - RPN calc tool

DPAmar
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Print stack first value

Let's add a useful, non-mathematical, unary operator: print. It would print stack's head as a decimal integer. The new code will be

  • Print (letter P, code 80)

Note that this operator will not consume the first stacked value : it will print it bu value remains unchanged

Let's start

  • Memory: empty
  • Cursor: first cell
  • Input: space separated integers and operators

Process

  • Leave an empty space (current number on stack is null)
  • While there is a char to read
    • subtract 32 and set else flag
    • if char is null : it's space
      • reset else flag, move to the right
    • subtract 10 (total 42), if char is null : it's multiply
      • reset else flag, multiply the 2 operands
    • subtract 1 (total 43), if char is null : it's addition
      • reset else flag, sum the 2 operands
    • subtract 2 (total 45), if char is null : it's subtraction
      • reset else flag, subtract the 2 operands
    • subtract 35 (total 80), if char is null : it's print
      • reset else flag, print first operand
    • otherwise
      • add 32 (to get the digit value)
      • add current number 10 times to current digit to get new current number
  • loop

Code

>,[                     leave empty space and read char
  let's track our target values here
  space 32
  multiply 42
  add 43
  subtract 45
  print 80
  digit 48 to 57

  >++++[-<-------->]+<  subtract 32
  [----------           subtract 10
  [-                    subtract 1
  [--                   subtract 2
  [>++++++[-<----->]+<  subtract 35
  [                     it's a digit
    >+++[-<++++++++>]<  add 32 to get digit value (and reset else flag)
    <[->++++++++++<]    add current number 10 times to current digit
    >[-<+>]             replace current number by current digit
  ]>[-                  now unwind cases: it's print
    <<<[->+>+<<]>[-<+>] copy number (to remain value unchanged after print)
    >[>>>>++++++++++<<< print copied value
    <[->+>>+>-[<-]<[->>   as a decimal number
    +<<<<[->>>+<<<]>]<<   ** part 3 **
    ]>+[-<+>]>>>[-]>[-<   ** part 4 **
    <<<+>>>>]<<<<]<[>++   ** part 5 **
    ++++[<++++++++>-]<-   ** part 6 **
    .[-]<]                ** part 7 **
    ++++++++++.[-]>     print newline (and reset newline char)
  ]<]>[-                next case: it's subtraction
    <<<[-<->]>          do the subtraction
  ]<]>[-                next case : it's add
    <<<[-<+>]>          do the addition
  ]<]>[-                next case : it's multiply
    <<<[->>+<<]>>[-<<<  do the multiplication
    [->+>+<<]>[-<+>]>>    ** part 2 **
    ]<<<[-]>>[-<<+>>]     ** part 3 **
  ]<]>[-                next case : it's space
    >                   move to next stack entry
  ]                     end of switch/case
<,]                     read char and loop

Final state

  • Memory: stack of integers
  • Cursor: after stack
  • Input: empty (read)
  • Output: unchanged

Test program

The program can be tested on its own.

You can try with input 6 8 * P 7 7 * P 1 P 7 7 * P + P for example. It should print 48, 49, 1, 49 and 50

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