AoC 2023 day 9 (Smalltalk)

#!/usr/local/bin/gst -q

Symbol extend [ value: arg  [^arg perform: self] ]

SequenceableCollection extend [
    " Returns collection of results from calling binBlock for each link pair "
    chain: binBlock [
        | res |
        res := self copyEmptyForCollect.
        self fold: [:curr :next | res add: (binBlock value: curr value: next). next].
        ^res
    ]
]

"
| Mainline
"
input := stdin lines contents collect: [:line | line subStrings collect: #asNumber].

part1 := 0.
part2 := 0.
input do: [:seq |
    row  := seq.
    mult := 1.

    [row conform: [:n | n = 0]] whileFalse: [
        " Part 1 is sum of lasts, part 2 is alternating sum of firsts "
        part1 := part1 + row last.
        part2 := part2 + (mult * row first).
        mult  := mult negated.

        row := row chain: [:a :b | b - a].
    ].
].


('Part 1: %1' % {part1}) displayNl.
('Part 2: %1' % {part2}) displayNl.