Ok, here it is.

I hate this even more than the Bingo. In particular, the text was very unclear about padding. Padding can basically be ignored in this exercise.

```
reuse [L42.is/AdamsTowel]
Fs = Load:{reuse[L42.is/FileSystem]}
Decoder = {
Map = Collection.map(key=S val=I.List)
class method I.List(S that) = This.map().val(key=that).val()
L={class method I.List (S that)=\()(
for c in that.split() \add(I(string=c)))}
@Cache.Lazy class method Map map()=\[
key=S"0" val=L(S"0000");
key=S"1" val=L(S"0001");
key=S"2" val=L(S"0010");
key=S"3" val=L(S"0011");
key=S"4" val=L(S"0100");
key=S"5" val=L(S"0101");
key=S"6" val=L(S"0110");
key=S"7" val=L(S"0111");
key=S"8" val=L(S"1000");
key=S"9" val=L(S"1001");
key=S"A" val=L(S"1010");
key=S"B" val=L(S"1011");
key=S"C" val=L(S"1100");
key=S"D" val=L(S"1101");
key=S"E" val=L(S"1110");
key=S"F" val=L(S"1111");
]}
Input = Data:{
mut I.List that
var I removed = 0I
mut method I b() = (
\removed(\removed+1I)
(left,removeLeft)=\#that
left
)
read method Bool isPadding() =
\that.size()<4I ||
\that.val(0I)+\that.val(1I)+\that.val(2I) ==0I
}
Packet = Data.AddList:Data:{ List = {}
I v,I t,Num val,List sub
}
ParsePacket = {
class method Packet (mut Input that) = {
v = \val(that,bits=3I)
t = \val(that,bits=3I)
if t==4I return \(v=v,t=t,val=this.vals(that),sub=\())
size = ( if that.b()==0I 15I else 11I )
psSize = \val(that,bits=size)
(removed) = that
if size==11I return \(v=v,t=t,val=Num(psSize),sub=\()(
for i in Range(psSize) \add(ParsePacket(that))
))
X[that.that().size()>=psSize]
return \(v=v,t=t,val=Num(psSize),sub=\()(
while that.removed()-removed<psSize \add(ParsePacket(that))
))
}
class method I val(mut Input that, I bits) = 0I.acc()(
for i in Range(bits) \val((\val*2I)+that.b())
)
class method Num vals(mut Input that) = {
(b0,b1,b2,b3,b4)= that
res = Num((b1*8I)+(b2*4I)+(b3*2I)+b4)
if b0==0I return res
pre = that.removed()
rec = \vals(that)
var seen = that.removed() - pre
mul = 1Num.acc()(while seen>3I (seen-=5I, \times(16Num)))
return (res*mul)+rec
}
}
Versions={class method I (Packet that) =
that.v().acc()(for p in that.sub() \add(This(p)))
}
Part2 = {class method Num (Packet that) = {
if that.t()==0I return 0Num.acc()(for p in that.sub() \add(This(p)))
if that.t()==1I return 1Num.acc()(for p in that.sub() \times(This(p)))
if that.t()==2I return This(that.sub().left()).acc()(for p in that.sub() \val(\val.min(This(p))))
if that.t()==3I return 0Num.acc()(for p in that.sub() \val(\val.max(This(p))))
if that.t()==4I return that.val()
(left,right) = that.sub()
if that.t()==5I return if This(left)>This(right) 1Num else 0Num
if that.t()==6I return if This(left)<This(right) 1Num else 0Num
if that.t()==7I return if This(left)==This(right) 1Num else 0Num
error X" unrecognized packet type"
}}
Main = (
input = Fs.Real.#$of().read(\"input").trim()
parsed = Input(\()(for c in input.split() for e in Decoder(c) \add(e)))
ps = Packet.List()(while !parsed.isPadding() \add(ParsePacket(parsed)))
Debug(Versions(ps.left()))//993
Debug(Part2(ps.left())) //144595909277
)
```

Note this funky code :-P

```
(left,removeLeft) = \#that
```

I'm not sure what to think about it. It is a cool way to go next after reading left, but it also feel like an abuse of the 'object decomposition' syntax.. any idea about it?

The more I use that pattern the more it feels ok... but I'm I just getting use to the anti-pattern, or is it actually a good way to express stuff?

Consider this other use of the same idea:

```
(b0,b1,b2,b3,b4) = that
```

Here I extract 5 bits from the input. This is nice and readable, and uses the same pattern of the 'removeLeft' above.

## Top comments (0)