operator: smap-window

    description:
        smap-window[op, w] seq
        cuts seq into width w n-grams, and applies op to them
        eg: smap-window[op, 3] (|a> . |b> . |c> . |d> . |e>)
        runs:
        op (|a> . |b> . |c>)
        op (|b> . |c> . |d>)
        op (|c> . |d> . |e>)
        op (|d> . |e>)
        op (|e>)

    examples:
        merge-3 (*) #=> learn(|op: merged>, sselect[1,1] |_self>, sselect[1,1] |_self> __ sselect[2,2] |_self> __ sselect[3,3] |_self>)
        smap-window[merge-3, 3] ssplit |abcde>
        dump
            merged |a> => |a b c>
            merged |b> => |b c d>
            merged |c> => |c d e>
            merged |d> => |d e>
            merged |e> => |e>

    see also:
        map