unlambda

unlambda.coffee

keywords = ['k', 's', 'i', 'v', 'c', 'd', 'e']
code = ''
window.toPrint = ''
log = (s)-> window.toPrint += s 

car = (pair) -> pair[0]
cdr = (pair) -> pair[1]
cadr = (pair) -> car cdr pair
caddr = (pair) -> car cdr cdr pair

isPair = (p) -> Array.isArray(p)
Token = (a, b)->
  return [a,b]
  
parse = () ->
  readChar = (check) ->
    [ret, code...] = code
    if check and !ret? then throw new Error 'Unexpected end of file'
    ret
    
  eatComment = ()->
    eatComment() unless readChar() == '\n'
  
  ch = readChar().toLowerCase()
  if ch == '' then throw new Error 'Unexpected end of file'
  if /\s/.test ch then return parse code
  if ch == '`'
    op = parse code
    arg = parse code
    return Token op, arg
  if ch == '.'
    return Token 'pr', readChar(1)
  if ch == 'r'
    return Token 'pr', '\n'
  if ch == '@'
    return Token 'rd'
  if ch == '?'
    return Token 'rc', readChar(1)
  if ch == '|'
    return Token 'pc'
  if ch in keywords
    return Token ch
  
  throw new Error "Wrong #{ch}"

unparse = (exp) ->
  if isPair car exp
    log '`'
    unparse car exp
    unparse cdr exp
  else
    x = car exp
    switch x
      when 'k' 
        log 'k'
      when 'k1'
        log '`', 'k'
        unparse cadr expr
      when 's' 
        log 's'
      when 's1' 
        log '`', 's'
        unparse cadr exp
      when 's2'
        log '`', '`', 's'
        unparse cadr exp
        unparse caddr exp
      when 'i'
        log 'i'
      when 'v'
        log 'v'
      when 'c'
        log 'v'
      when 'c1'
        log 'continuation'
      when 'd'
        log 'd'
      when 'd1'
        log '`', 'd'
        unparse cadr exp
      when 'e'
        log 'e'
      when 'pr'
        if (cadr exp) == '\n'
            log '\n'
          else
            log '.'
            log cadr exp
      when 'rd'
        log '@'
      when 'rc'
        log '?'
        log cadr exp
      when 'pc'
        log '|'
      else
        throw new Error "err#{x}"
      
   
ev = (exp) ->
  if isPair car exp
    op = ev car exp
    if car op == 'd'
     return Token 'd1', cdr exp
    else
     return ap op, ev cdr exp
  else
    return exp

ap = (exp, arg)
  switch car exp
    when 'k' then Token 'k1', arg
    when 'k1' then cadr expr
    when 's' then Token 's1', arg
    when 's1' then Token 's2', cadr exp, arg
    when 's2' then ev Token('')
    
    
code = '''
```s``s``sii`ki
  `k.*``s``s`ks
 ``s`k`s`ks``s``s`ks``s`k`s`kr``s`k`sikk
  `k``s`ksk
'''
unparse(parse(code))