add open, close, read, write

[enricozb]

Adds OPEN_FILE, CLOSE_FILE, READ_LINE, READ_CHAR, and WRITE IO functions. Since the read and write operations take in a file descriptor, I've also reserved numbers 0 1 and 2 to have their usual FD meaning, so users can print to stderr, read from stdin, etc.

Here's an example:

type IO_T:
  Done { magic, expr }
  Call { magic, func, argm, cont }

def IO_T/MAGIC:
  return (0xD0CA11, 0xFF1FF1)

def IO_T/wrap(x):
  return IO_T/Done(IO_T/MAGIC, x)

def IO_T/bind(a, b):
  match a:
    case IO_T/Done:
      return b(a.expr)
    case IO_T/Call:
      return IO_T/Call(IO_T/MAGIC, a.func, a.argm, lambda x: IO_T/bind(a.cont(x), b))

def call_io(func, argm):
  return IO_T/Call(IO_T/MAGIC, func, argm, lambda x: IO_T/Done(IO_T/MAGIC, x))

def main:
  do IO_T:
    * <- call_io("WRITE", (1, "what is your name?\n"))
    name <- call_io("READ_LINE", 0)
    * <- call_io("WRITE", (1, "Hello, '"))
    * <- call_io("WRITE", (1, name))
    * <- call_io("WRITE", (1, "'!\n"))

    file <- call_io("OPEN_FILE", ("testing.txt", "w"))
    * <- call_io("WRITE", (file, "Your name is: "))
    * <- call_io("WRITE", (file, name))
    * <- call_io("WRITE", (file, "!"))
    * <- call_io("CLOSE_FILE", file)

    return 42

[VictorTaelin]

let's keep the readback functions prefixed by read_ as a convention

[enricozb]

What about functions that are inverses of readback functions? I named it port_to_ctr b/c I also created a ctr_to_port. What do you think we should call the functions that convert Ctr to Port?

[VictorTaelin]

I prefer readback_x and inject_x or create_x for the inverses, because it is consistent with how it is in other codes of the past.

[VictorTaelin]

Is that example right? Isn't it with instead of do? Also IO_T should be renamed to IO, and it should be a builtin on Bend.

[edusporto]

@VictorTaelin That example was fixed in #369, it should be correct now

[VictorTaelin]

oh sure, my bad