// Ackermann function

`export ack : Fn[m; n] $ (
    t : `type m;
    ? |(t != `type n) {
        `panic "m and n must be the same type"
    }
    ? |(t = Int_signed; t = Float) {
        ? |(m < 0; n < 0) { `return 0 }
    }
    ? {
        m = 0 { n + 1 }
        &(m > 0; n = 0) { ack `call (m - 1; 1) }
        { ack `call (m - 1; ack `call (m; n - 1)) }
    }
)

`export ack_string : Fn[m; n] $ (
    "#MAGENTA#ack#(#CYAN#%#, #CYAN#%#) #WHITE#=# #GREEN#%#\n" `format (m; n; ack `call (m; n))
)

`is_main Fn $ (
    ( args ) : `use "sys"
    ? 4 != `length args {
         `return `error String $ (
            "Got: "; " " `join args; "\n"
            "Usage: "; args `get 0; " "; args `get 1; " <m> <n>\n"
         )
    }
    `print ack_string `call (U64 $ args `get -2; U64 $ args `get -1)
)