Russ Cox
@swtch.com
Heading home from #GopherCon 2025 in NYC. As usual, many people asked how to get one of the amazing Go gopher Hawaiian shirts by Renee French. I've posted the details at github.com/rsc/gophersh.... (I know one person who has made pajama pants with the pattern. Socks might be nice too.) Enjoy!
August 29, 2025 at 4:02 PM
Heading home from #GopherCon 2025 in NYC. As usual, many people asked how to get one of the amazing Go gopher Hawaiian shirts by Renee French. I've posted the details at github.com/rsc/gophersh.... (I know one person who has made pajama pants with the pattern. Socks might be nice too.) Enjoy!
Day 4 part 2 #AdventOfCode
d shift3 m produces the 3 matrices shifted by d*-1 0 1.
d MAS m identifies the A in MAS in direction d.
d xMAS m identifies the A in MAS in direction d or -d.
xMAS m identifies the A in an X-MAS.
d shift3 m produces the 3 matrices shifted by d*-1 0 1.
d MAS m identifies the A in MAS in direction d.
d xMAS m identifies the A in MAS in direction d or -d.
xMAS m identifies the A in an X-MAS.
December 4, 2024 at 2:48 PM
Day 4 part 2 #AdventOfCode
d shift3 m produces the 3 matrices shifted by d*-1 0 1.
d MAS m identifies the A in MAS in direction d.
d xMAS m identifies the A in MAS in direction d or -d.
xMAS m identifies the A in an X-MAS.
d shift3 m produces the 3 matrices shifted by d*-1 0 1.
d MAS m identifies the A in MAS in direction d.
d xMAS m identifies the A in MAS in direction d or -d.
xMAS m identifies the A in an X-MAS.
Day 4 part 1 adventofcode.com/2024/day/4 #AdventOfCode
pad dot-pads the matrix to avoid wraparound.
x y shift m rotates the matrix x left, y down.
d(=x y) shift4 m produces the 4 matrices shifted by d*0 1 2 3.
d XMAS m identifies the X in XMAS in direction d.
pad dot-pads the matrix to avoid wraparound.
x y shift m rotates the matrix x left, y down.
d(=x y) shift4 m produces the 4 matrices shifted by d*0 1 2 3.
d XMAS m identifies the X in XMAS in direction d.
![sample = read "sample.txt"
input = read "input.txt"
dirs = d, -d=4 2 rho 1 0, 0 1, 1 1, -1 1
op T x = transp x
op pad x = T (T x, '.'), '.'
op d shift m = T d[2] rot T d[1] rot m
op d shift4 m = (0 1 2 3 @* d) @shift m
op d XMAS m = T and/ 'XMAS' == T d shift4 m
op solve x = +/+/+/ dirs @XMAS pad x
solve sample
solve input](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:a4slcmeql3w6vsdbjbcgxd3m/bafkreiazvpevui6fije2gmsl66omgknsaihadye4ujbrmdymuspxxtbhlu@jpeg)
December 4, 2024 at 2:42 PM
Day 4 part 1 adventofcode.com/2024/day/4 #AdventOfCode
pad dot-pads the matrix to avoid wraparound.
x y shift m rotates the matrix x left, y down.
d(=x y) shift4 m produces the 4 matrices shifted by d*0 1 2 3.
d XMAS m identifies the X in XMAS in direction d.
pad dot-pads the matrix to avoid wraparound.
x y shift m rotates the matrix x left, y down.
d(=x y) shift4 m produces the 4 matrices shifted by d*0 1 2 3.
d XMAS m identifies the X in XMAS in direction d.
Day 3 part 2.
The function 'c step2 s' is the updated state machine, with an extra value tracking whether mul(x,y) is enabled. step2 takes care of do()/don't() processing and invokes 'step' (from part 1) to handle mul(x,y) when appropriate.
The function 'c step2 s' is the updated state machine, with an extra value tracking whether mul(x,y) is enabled. step2 takes care of do()/don't() processing and invokes 'step' (from part 1) to handle mul(x,y) when appropriate.
![op c step2 s =
(rho s) == 0: c step2 s step2 (0 0 0 0 +1)
c == 'd': -1, 0, 0, s[4], s[5] # do() ...
(s[1] == -1) and c == 'o': -2, 0, 0, s[4], s[5]
(s[1] == -2) and c == '(': -3, 0, 0, s[4], s[5]
(s[1] == -3) and c == ')': 0, 0, 0, s[4], +1
(s[1] == -2) and c == 'n': -4, 0, 0, s[4], s[5] # or don't()...
(s[1] == -4) and c == '\'': -5, 0, 0, s[4], s[5]
(s[1] == -5) and c == 't': -6, 0, 0, s[4], s[5]
(s[1] == -6) and c == '(': -7, 0, 0, s[4], s[5]
(s[1] == -7) and c == ')': 0, 0, 0, s[4], -1
s[5] == +1: (c step -1 drop s), s[5]
0, 0, 0, s[4], s[5]
op solve2 x = (step2/ flip x)[4]
solve2 sample
solve2 input](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:a4slcmeql3w6vsdbjbcgxd3m/bafkreihilz2oldnlyi3eoafimd7caaxlfrcu5eenhm3yn4wqhsvhln7vv4@jpeg)
December 3, 2024 at 6:27 AM
Day 3 part 2.
The function 'c step2 s' is the updated state machine, with an extra value tracking whether mul(x,y) is enabled. step2 takes care of do()/don't() processing and invokes 'step' (from part 1) to handle mul(x,y) when appropriate.
The function 'c step2 s' is the updated state machine, with an extra value tracking whether mul(x,y) is enabled. step2 takes care of do()/don't() processing and invokes 'step' (from part 1) to handle mul(x,y) when appropriate.
Day 3 part 1.
The function 'c step s' steps the state machine state s to incorporate the new character c.
(step/ flip x) runs the state machine over the whole string, left to right.
The reduction base case for "...yz" is 'y' step 'z', which step rewrites to ('y' step 'z' step initial-state).
The function 'c step s' steps the state machine state s to incorporate the new character c.
(step/ flip x) runs the state machine over the whole string, left to right.
The reduction base case for "...yz" is 'y' step 'z', which step rewrites to ('y' step 'z' step initial-state).
![sample = read "sample.txt"
input = read "input1.txt"
digits = "0123456789"
op i atoi c = (i*10) + (code c) - (code '0')
op c step s =
(rho s) == 0: c step s step (0 0 0 0)
c == 'm': 1, 0, 0, s[4]
(s[1] == 1) and c == 'u': 2, 0, 0, s[4]
(s[1] == 2) and c == 'l': 3, 0, 0, s[4]
(s[1] == 3) and c == '(': 4, 0, 0, s[4]
(s[1] == 4) and c in digits: 4, (s[2] atoi c), 0, s[4]
(s[1] == 4) and (s[2] < 1000) and c == ',': 5, s[2], 0, s[4]
(s[1] == 5) and c in digits: 5, s[2], (s[3] atoi c), s[4]
(s[1] == 5) and (s[3] < 1000) and c == ')': 0, 0, 0, s[4]+s[2]*s[3]
0, 0, 0, s[4]
op solve x = (step/ flip x)[4]
solve sample
solve input](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:a4slcmeql3w6vsdbjbcgxd3m/bafkreiahk4xtn6ge7trxtpxeeobedw5ayr3lwr2fppn3isadkx7r72cyvm@jpeg)
December 3, 2024 at 6:25 AM
Day 3 part 1.
The function 'c step s' steps the state machine state s to incorporate the new character c.
(step/ flip x) runs the state machine over the whole string, left to right.
The reduction base case for "...yz" is 'y' step 'z', which step rewrites to ('y' step 'z' step initial-state).
The function 'c step s' steps the state machine state s to incorporate the new character c.
(step/ flip x) runs the state machine over the whole string, left to right.
The reduction base case for "...yz" is 'y' step 'z', which step rewrites to ('y' step 'z' step initial-state).