AoC day 9, Smalltalk

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

OrderedCollection extend [
    canSum: num [
        " XXX: cleaner way to do this? "
        (0 to: self size - 2) do: [ :i |
            (self readStream copyFrom: i + 1 to: self size - 1) do: [ :j |
                ((self at: i + 1) + j = num) ifTrue: [ ^true ]
            ]
        ].
        ^false
    ]

    findBadSum [
        | rs targ window |
        rs := ReadStream on: self.
        window := (rs copyFrom: 0 to: 24).

        (rs position: 25) do: [ :next |
            (window canSum: next) ifFalse: [ ^next ].
            window removeFirst.
            window addLast: next.
        ].
        ^nil
    ]

    findSumRange: targ [
        | i j sum |
        i := 1.
        j := 1.
        sum := self at: 1.

        [ sum == targ ] whileFalse: [
            (sum < targ) ifTrue: [ j := j + 1.  sum := sum + (self at: j) ].
            (sum > targ) ifTrue: [ sum := sum - (self at: i).  i := i + 1 ].
        ].

        ^Array with: i - 1 with: j - 1.
    ]
]

"
|  Mainline
"
list := OrderedCollection new.
stdin linesDo: [ :line | list addLast: line asNumber ].

part1 := list findBadSum.
stdout nextPutAll: ('Part 1: ', part1 asString); nl.

range    := list findSumRange: part1.
interval := list readStream copyFrom: range first to: range second.

part2 := (interval inject: part1 into: [ :a :b | a min: b ])
       + (interval inject: 0     into: [ :a :b | a max: b ]).

stdout nextPutAll: ('Part 2: ', part2 asString); nl.