How to read char without echo

Question

In (*1) we have example how to turn off echo when use getChar in haskell. The idea is we can turn off echo using hSetEcho stdin False.

I would like do the same thing in Idris. Do I have a way?

(*1) Haskell read raw keyboard input

Answer 1

You might want to use the curses bindings.

If this is too heavy for your usage, you can write C code that handles this for your terminal, and use that code via FFI interfaces. For example, you can use termios.hfor Linux terminals like this:

termops.c:

 #include "termops.h"
 #include <termios.h>

 void set_echo(int fd) {
  struct termios term;
  tcgetattr(0, &term);
  term.c_lflag |= ECHO;
  tcsetattr(fd, TCSAFLUSH, &term);
 }

 void unset_echo(int fd) {
   struct termios term;
   tcgetattr(0, &term);
   term.c_lflag &= ~ECHO;
   tcsetattr(fd, TCSAFLUSH, &term);
 }

termops.h:

void set_echo(int fd);
void unset_echo(int fd);

termops.idr:

%include C "termops.h"

setEcho : IO ()
setEcho = foreign FFI_C "set_echo" (Int -> IO ()) 0

unsetEcho : IO ()
unsetEcho = foreign FFI_C "unset_echo" (Int -> IO ()) 0

getPasswd : IO String
getPasswd = do
  c <- getChar
  if c == '\n'
  then pure ""
  else do rek <- getPasswd
          pure $ strCons c rek

main : IO ()
main = do
  unsetEcho
  passwd <- getPasswd
  setEcho
  printLn passwd

To compile and link the C library, then use idris termops.idr --cg-opt "termops.c".