https://github.com/carrotflakes/uttr

otterl.uttr

//// Otter Lisp

// string utils
strlen
  ("", n) = n,
  (c:xs, n) = strlen(xs, n+1)
strLen s = strlen(s, 0)

strCat
  [] = "",
  x:xs = x + strCat(xs)

strrev
  ("", s) = s,
  (c:xs, s) = strrev(xs, c:s)
strRev s = strCat(strrev(s, []))

x = strRev("hogehoge")

// input streams
// stream := [str, len, pos]
makeStream s = [s, strLen(s), 0]
streamStr str:len:pos:[] = str
streamLen str:len:pos:[] = len
streamPos str:len:pos:[] = pos

doInRange (s, fn)
  | streamPos(s) >= streamLen(s) = false
  | true = fn(s)

streamAt s = doInRange(s, [(str:len:pos:[]) = str[pos]])
streamNext s = doInRange(s, [(str:len:pos:[]) = [str, len, pos+1]])

runWhile (pred, fn, state, s)
  | streamAt(s) == false = [false, state, s]
  | pred(streamAt(s)) = [true, state, streamNext(s)]
  | true = runWhile(pred, fn, fn(s, state), streamNext(s))

// stacks
// stack := [...]
stackPop x:xs = [x, xs]
stackPush (o, s) = o:s

readstring s = runWhile([c = c == "\""], [(s,state) = streamAt(s):state], [], s)
readString s = 
  [false:_:s:[] = false,  // EOF
   true:state:s:[] = [strCat(state), s]](readstring(s))

readParen s = "????"