nishio/FORTH-on-browser

FORTH on browser

HISTORY

• 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
  else
    dup 1 - fact
    *
  then
;

• 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)

License

GPLv3 (c) NISHIO Hirokazu 2012

Thanks

Paweł Marczewski contributed much to the project.