FORTH on browser




Call stack:


  • Milestome1: simple stack-based execution

    • the user will be able to input the words in the interpreter to execute them
    • the webpage will show the current state of the stack (as a list on the right side of the terminal)
    • simple words: numbers, arithmetic (+,-,*,/), stack manipulation (dup, drop, swap etc.), printing the result (.)
    • (no procedures yet)
    • “1 2 +” returns “3”
  • Milestone2: procedures - (: double 2 * ;) - “compilation mode / run mode” distinction - virtual machine: the target code will consist not of words, but of operations: call(word), push(number) - compile and run mode: the words will get executed in run mode, and transformed to the target code in compile mode - immediate words: some words will get executed in compile mode - ‘:’ word will enter compile mode, compile words until ‘;’ (a definition), and create a new word - comments (‘(‘ word)

    • ‘(‘ will read input until ‘)’ and disregard it
    • source textbox, as with other interpreters
    • factorial demonstration
      • boolean type and literals (true, false), logic operations (and, or, not)
      • number comparison (=, < etc.),
      • conditionals (if..then, if..else..then), loops (repeat..until)
      • virtual machine will get branching instructions: goto(number), goto-if-false(number)
      • ‘if’ will be an immediate word that reads words until ‘else’ and ‘then’, and adds appropriate branching instruction
      • the same for ‘repeat..until’
: fact
  dup 0 = if
    drop 1
    dup 1 - fact
  • Milestone3: variable and debugger
    • variables (variable x), storing and fetching them (x @, x !)
    • other Forth loop constructs (including do..loop with a loop index)
      • original Forth used raw pointers (running ‘x’ puts 123823 on the stack), we can do something nicer (running ‘x’ will put <x> on the stack).
    • debugger:
      • show execution state with call stack and all the words, [step into] and [step over] buttons
      • being able to display and step over execution (this is probably a big one)


GPLv3 (c) NISHIO Hirokazu 2012


Paweł Marczewski contributed much to the project.

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