prelude.py 文件源码

def scanr(col, func=add, acc=None):
    '''
    Use a given accumulator value to build a list of values obtained
    by repeatedly applying acc = func(next(list), acc) from the right.

    WARNING: Right folds and scans will blow up for infinite generators!
    '''
    try:
        col = reversed(col)
    except TypeError:
        col = reversed(list(col))

    if acc is not None:
        col = chain([acc], col)

    return list(itools.accumulate(col, func))