• sof's avatar
    [project @ 2005-05-06 00:30:56 by sof] · 4224e90e
    sof authored
    [mingw only]
    Work around bug in win32 Console API which showed up in the GHCi UI:
    if the user typed in characters prior to the appearance of the prompt,
    the first of these characters always came out as a 'g'. The GHCi UI does
    for good reasons one-character reads from 'stdin', which causes the
    underlying APIs to become confused. A simple repro case is the following
    piece of C code:
    #include <stdio.h>
    #include <windows.h>
    int main()
        char ch1,ch2;
        HANDLE hStdIn = GetStdHandle(STD_INPUT_HANDLE);
        DWORD dw;
        /* Type in some characters before the prompt appears and be amused.. */
        sleep(1000); printf("? ");
    /*  or, if you want to use libc:
        read(0,&ch1,1); read(0,&ch2,1); */
        printf("%c%c\n", ch1,ch2);
        return 0;
    This happens across win32 OSes, and I can't see anything untoward as far
    as API usage goes (the GHC IO implementation uses read(), but that
    reduces to ReadConsoleA() calls.) People inside the Behemoth might want
    to have a closer look at this..
    Not much we can do about this except work around the problem by flushing
    the input buffer prior to reading from stdin. Not ideal, as type-ahead
    is a useful feature. Flushing is handled by GHC.ConsoleHandler.flushConsole
    Merge to STABLE.