Q (equational Programming Language) - Examples

Examples

A "hello world" example:

hello = writes "Hello, world!\n";

The following function generates the "stream" (a.k.a. infinite list) of all prime numbers:

primes = sieve (ints 2); ints N = bin N (ints (N+1)); sieve (bin X Xs) = bin X (sieve (filter (ndivby X) Xs)); ndivby M N = N mod M <> 0;

An algorithm to solve the "N queens" problem, using backtracking:

queens N = search N 1 1 ; search N I J P = write P || writes "\n" if I>N; = search N (I+1) 1 (P++) || fail if safe (I,J) P; = search N I (J+1) P if JA tiny system programming example (fetch a file from a WWW server over a socket):

/* make sure SIGPIPE (broken connection signal) is ignored */ def _ = trap SIG_IGN SIGPIPE; /* fetch a file from an http server (port 80) */ http HOST NAME = close FD || bstr REPLY where FD:Int = socket AF_INET SOCK_STREAM 0, _ = connect FD (HOST,80), _ = send FD 0 (bytestr (sprintf "GET %s\r\n\r\n" NAME)), REPLY = recv_loop FD (bytestr ""); /* read data in 64K chunks */ recv_loop FD S = recv_loop FD (S++T) if #T>0 where T:ByteStr = recv FD MSG_WAITALL (64*1024); = S otherwise;

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