VVTB interpreter

vvtb.coffee

intro = [
  '=======================================',
  'VVTB (Very Very Tiny Basic) interpreter',
  '(c) 2012 Forest Belton (case)',
  '======================================='
]

prgm = {}
vars = {}

add_msg = (msg, error) ->
  classes = if error is true then 'error' else ''
  $('#msgs').append "<div class=\"#{classes}\">#{msg}</div>"

getlines = () ->
  lines = []
  for line of prgm
    lines.push parseInt(line)
  return lines.sort (a,b) -> a - b

print_prgm = () ->
  keys = getlines()
  for key in keys
    add_msg prgm[key].raw, false

run_prgm = () ->
  lines = getlines()
  pc    = lines[0]
  while prgm[pc] isnt undefined
    console.log "PC: #{pc}"
    pc = eval_prgm pc, prgm[pc].stmt, lines

eval_prgm = (pc, stmt, lines) ->
  switch stmt.type
    when 'goto'  then return stmt.line
    when 'let'   then vars[stmt.dest] = eval_expr stmt.val
    when 'print' then add_msg (stmt.items.map(eval_expr).join ''), false
    when 'if'    then if stmt.cond.op eval_expr(stmt.cond.left), eval_expr(stmt.cond.right) then return stmt.line

  for line in lines
    if line > pc
      return line
  return undefined

eval_expr = (stmt) ->
  if typeof stmt is 'object'
    return stmt.op eval_expr(stmt.left), eval_expr(stmt.right)
  else if typeof stmt is 'string'
    return vars[stmt]
  else
    return stmt

readline = () ->
  add_msg '> ' + $('#input').val(), false

  try
    line = vvtb.parse $('#input').val() + '\n'
  catch error
    add_msg error.message, true
    return

  switch line.stmt.type
    when 'new'    then prgm = {}
    when 'list'   then print_prgm()
    when 'run'    then run_prgm()
    when 'delete' then delete prgm[line.line]
    else               prgm[line.line] = { 'raw' : $('#input').val(), 'stmt' : line.stmt }

$('document').ready () ->
  for line in intro
    add_msg line, false

  $('#input').focus()
  $(document).click () ->
    $('#input').focus()

  $('#input').keydown (e) ->
    if e.which is 13
      readline()
      $('#input').val ''

vvtb.g

{
  function make_stmt(s, args) {
    var stmt = { 'type' : s };
    
    switch(s) {
      case 'let':
        stmt['dest'] = args[0];
        stmt['val']  = args[1];
      break;
      
      case 'if':
        stmt['cond'] = args[0];
        stmt['line'] = args[1];
      break;
      
      case 'print':
        stmt['items'] = args[0];
      break;
      
      case 'rem':
        stmt['comment'] = args[0];
      break;
      
      case 'goto':
        stmt['line'] = args[0];
      break;
    }

    return stmt;
  }
  
  ops = {
    '+'  : function(x,y) { return x + y  },
    '-'  : function(x,y) { return x - y  },
    '*'  : function(x,y) { return x * y  },
    '/'  : function(x,y) { return x / y  },
    '<'  : function(x,y) { return x < y  },
    '>'  : function(x,y) { return x > y  },
    '='  : function(x,y) { return x == y },
    '<>' : function(x,y) { return x != y },
    '<=' : function(x,y) { return x <= y },
    '>=' : function(x,y) { return x >= y },
  }
}

line
 = line:cmd_line ws '\n'  { return line }
 / line:prog_line ws '\n' { return line }

cmd_line
 = 'RUN'  { return { 'stmt' : make_stmt('run')  } }
 / 'LIST' { return { 'stmt' : make_stmt('list') } }
 / 'NEW'  { return { 'stmt' : make_stmt('new')  } }
 / 'QUIT' { return { 'stmt' : make_stmt('quit') } }

prog_line
 = line:number ws s:stmt? { if(s=='') s = make_stmt('delete',[]); return { 'line' : line, 'stmt' : s} }

stmt
 = 'LET' ws v:variable ws '=' ws e:expr { return make_stmt('let', [v, e]) }
 / 'IF' ws cond:test ws 'THEN' ws line:number { return make_stmt('if', [cond, line]) }
 / 'PRINT' ws p:print_items { return make_stmt('print', [p]) }
 / 'REM' ws line:[^\n]+ { return make_stmt('rem', [line.join('')]) }
 / 'GOTO' ws line:number { return make_stmt('goto', [line]) }

print_items
 = p:print_item ws ',' ws ps:print_items { ps.unshift(p); return ps }
 / p:print_item ws ';' ws ps:print_items { ps.unshift(p); return ps }
 / p:print_item { return [p] }

separator
 = ','
 / ';'

print_item
 = expr
 / string

test
 = left:expr ws comp:comparison ws right:expr { return { 'left' : left, 'right' : right, 'op' : ops[comp] } }

comparison
 = '='
 / '<>'
 / '<'
 / '<='
 / '>'
 / '>='

expr
 = left:secondary ws op:[+-] ws right:expr { return { 'op' : ops[op], 'left' : left, 'right' : right } }
 / secondary

secondary
 = left:primary ws op:[*/] ws right:secondary { return { 'op' : ops[op], 'left' : left, 'right' : right } }
 / p:primary { return p }

primary
 = '(' e:expr ')' { return e }
 / variable
 / number

string
 = ["] data:[^"]+ ["] { return data.join('') }

variable
 = [A-Z]

number
 = digits:[0-9]+ { return parseInt(digits.join('')) }

ws
 = [ \t\v\f]*