prelude.bprog

repeat
{
    swap [ ] cons swap times { dup head [ ] cons append } tail
}
fun



odd
{
    dup 2 div swap 2 / == if False True
}
fun



fizzbuzz
{
    map {
        dup 15 % 0 ==
        if { pop " fizzbuzz " }
        {
            dup 3 % 0 ==
            if { pop " fizz " }
            {
                dup 5 % 0 ==
                if { pop " buzz " } ()
            }
        }
    }
}
fun


concat
{
    [ ] foldl append
}
fun


reverse
{
    [ ] foldl { [ ] cons swap append }
}
fun

:
{
    [ ]  cons
}
fun


x:xs
{
    dup tail swap head
}
fun


xs:x
{
    dup head swap tail
}
fun


last
{
    dup empty
    if
    { pop err " err: last used with empty list " }
    {
        dup length 1 ==
        if { head }
        { tail last }
    }
}
fun


init
{
    dup empty
    if
    { pop err " err: init used with empty list " }
    {
        dup length 1 ==
        if { pop [ ] }
        { reverse x:xs pop reverse }
    }
}
fun


range
{
    dup : swap 1 - times { dup head 1 - swap cons }
}
fun


factorial
{
    dup 0 <
    if
    { err " err: factorial is not defined for negative numbers! " }
    { range 1 foldl * }
}
fun


fib
{
    dup 1 <
    if
    { pop [ ] }
    {
        [ 1 0 ] swap 1 - times
        { dup dup head swap tail head + swap cons }
        tail reverse
    }
}
fun


nth_fib
{
    dup 1 <
    if
    { pop [ ] }
    {
        [ 1 0 ] swap 1 - times
        { dup dup head swap tail head + swap cons }
        head
    }
}
fun