$$
% Typography and symbols
\newcommand{\msf}[1]{\mathsf{#1}}
\newcommand{\ctx}{\Gamma}
\newcommand{\qamp}{&\quad}
\newcommand{\qqamp}{&&\quad}
\newcommand{\Coloneqq}{::=}
\newcommand{\proves}{\vdash}
\newcommand{\star}[1]{#1^{*}}
\newcommand{\eps}{\varepsilon}
\newcommand{\nul}{\varnothing}
\newcommand{\brc}[1]{\{{#1}\}}
\newcommand{\binopm}[2]{#1~\bar{\oplus}~#2}
\newcommand{\mag}[1]{|{#1}|}
\newcommand{\aequiv}{\equiv_\alpha}
\newcommand{\semi}[2]{{#1};~{#2}}
% Untyped lambda calculus
\newcommand{\fun}[2]{\lambda ~ {#1} ~ . ~ {#2}}
\newcommand{\app}[2]{#1 ~ #2}
\newcommand{\fix}[3]{\msf{fix}~({#1} : {#2}) ~ . ~ #3 }
\newcommand{\truet}{\msf{true}}
\newcommand{\falset}{\msf{false}}
\newcommand{\define}[2]{{#1} \triangleq {#2}}
% Typed lambda calculus - expressions
\newcommand{\funt}[3]{\lambda ~ \left(#1 : #2\right) ~ . ~ #3}
\newcommand{\lett}[4]{\msf{let} ~ \hasType{#1}{#2} = #3 ~ \msf{in} ~ #4}
\newcommand{\letrec}[4]{\msf{letrec} ~ \hasType{#1}{#2} = #3 ~ \msf{in} ~ #4}a
\newcommand{\ift}[3]{\msf{if} ~ {#1} ~ \msf{then} ~ {#2} ~ \msf{else} ~ {#3}}
\newcommand{\rec}[5]{\msf{rec}(#1; ~ #2.#3.#4)(#5)}
\newcommand{\case}[5]{\msf{case} ~ {#1} ~ \{ L(#2) \to #3 \mid R(#4) \to #5 \}}
\newcommand{\pair}[2]{\left({#1},~{#2}\right)}
\newcommand{\proj}[2]{#1 . #2}
\newcommand{\inj}[3]{\msf{inj} ~ #1 = #2 ~ \msf{as} ~ #3}
\newcommand{\letv}[3]{\msf{let} ~ {#1} = {#2} ~ \msf{in} ~ {#3}}
\newcommand{\fold}[2]{\msf{fold}~{#1}~\msf{as}~{#2}}
\newcommand{\unfold}[1]{\msf{unfold}~{#1}}
\newcommand{\poly}[2]{\Lambda~{#1}~.~ #2}
\newcommand{\polyapp}[2]{{#1}~\left[{#2}\right]}
\newcommand{\export}[3]{\msf{export}~ #1 ~\msf{without}~{#2}~\msf{as}~ #3}
\newcommand{\import}[4]{\msf{import} ~ ({#1}, {#2}) = {#3} ~ \msf{in} ~ #4}
% Typed lambda calculus - types
\newcommand{\tnum}{\msf{num}}
\newcommand{\tstr}{\msf{string}}
\newcommand{\tint}{\msf{int}}
\newcommand{\tbool}{\msf{bool}}
\newcommand{\tfun}[2]{#1 \rightarrow #2}
\newcommand{\tprod}[2]{#1 \times #2}
\newcommand{\tsum}[2]{#1 + #2}
\newcommand{\trec}[2]{\mu~{#1}~.~{#2}}
\newcommand{\tvoid}{\msf{void}}
\newcommand{\tunit}{\msf{unit}}
\newcommand{\tpoly}[2]{\forall~{#1}~.~{#2}}
\newcommand{\tmod}[2]{\exists ~ {#1} ~ . ~ #2}
% WebAssembly
\newcommand{\wconst}[1]{\msf{i32.const}~{#1}}
\newcommand{\wbinop}[1]{\msf{i32}.{#1}}
\newcommand{\wgetlocal}[1]{\msf{get\_local}~{#1}}
\newcommand{\wsetlocal}[1]{\msf{set\_local}~{#1}}
\newcommand{\wgetglobal}[1]{\msf{get\_global}~{#1}}
\newcommand{\wsetglobal}[1]{\msf{set\_global}~{#1}}
\newcommand{\wload}{\msf{i32.load}}
\newcommand{\wstore}{\msf{i32.store}}
\newcommand{\wsize}{\msf{memory.size}}
\newcommand{\wgrow}{\msf{memory.grow}}
\newcommand{\wunreachable}{\msf{unreachable}}
\newcommand{\wblock}[1]{\msf{block}~{#1}}
\newcommand{\wloop}[1]{\msf{loop}~{#1}}
\newcommand{\wbr}[1]{\msf{br}~{#1}}
\newcommand{\wbrif}[1]{\msf{br\_if}~{#1}}
\newcommand{\wreturn}{\msf{return}}
\newcommand{\wcall}[1]{\msf{call}~{#1}}
\newcommand{\wlabel}[2]{\msf{label}~\{#1\}~{#2}}
\newcommand{\wframe}[2]{\msf{frame}~({#1}, {#2})}
\newcommand{\wtrapping}{\msf{trapping}}
\newcommand{\wbreaking}[1]{\msf{breaking}~{#1}}
\newcommand{\wreturning}[1]{\msf{returning}~{#1}}
\newcommand{\wconfig}[5]{\{\msf{module}{:}~{#1};~\msf{mem}{:}~{#2};~\msf{locals}{:}~{#3};~\msf{stack}{:}~{#4};~\msf{instrs}{:}~{#5}\}}
\newcommand{\wfunc}[4]{\{\msf{params}{:}~{#1};~\msf{locals}{:}~{#2};~\msf{return}~{#3};~\msf{body}{:}~{#4}\}}
\newcommand{\wmodule}[1]{\{\msf{funcs}{:}~{#1}\}}
\newcommand{\wcg}{\msf{globals}}
\newcommand{\wcf}{\msf{funcs}}
\newcommand{\wci}{\msf{instrs}}
\newcommand{\wcs}{\msf{stack}}
\newcommand{\wcl}{\msf{locals}}
\newcommand{\wclab}{\msf{labels}}
\newcommand{\wcm}{\msf{mem}}
\newcommand{\wcmod}{\msf{module}}
\newcommand{\wsteps}[2]{\steps{\brc{#1}}{\brc{#2}}}
\newcommand{\with}{\underline{\msf{with}}}
\newcommand{\wvalid}[2]{{#1} \vdash {#2}~\msf{valid}}
\newcommand{\wif}[2]{\msf{if}~{#1}~{\msf{else}}~{#2}}
\newcommand{\wfor}[4]{\msf{for}~(\msf{init}~{#1})~(\msf{cond}~{#2})~(\msf{post}~{#3})~{#4}}
% assign4.3 custom
\newcommand{\wtry}[2]{\msf{try}~{#1}~\msf{catch}~{#2}}
\newcommand{\wraise}{\msf{raise}}
\newcommand{\wraising}[1]{\msf{raising}~{#1}}
\newcommand{\wconst}[1]{\msf{i32.const}~{#1}}
\newcommand{\wbinop}[1]{\msf{i32}.{#1}}
\newcommand{\wgetlocal}[1]{\msf{get\_local}~{#1}}
\newcommand{\wsetlocal}[1]{\msf{set\_local}~{#1}}
\newcommand{\wgetglobal}[1]{\msf{get\_global}~{#1}}
\newcommand{\wsetglobal}[1]{\msf{set\_global}~{#1}}
\newcommand{\wload}{\msf{i32.load}}
\newcommand{\wstore}{\msf{i32.store}}
\newcommand{\wsize}{\msf{memory.size}}
\newcommand{\wgrow}{\msf{memory.grow}}
\newcommand{\wunreachable}{\msf{unreachable}}
\newcommand{\wblock}[1]{\msf{block}~{#1}}
\newcommand{\wloop}[1]{\msf{loop}~{#1}}
\newcommand{\wbr}[1]{\msf{br}~{#1}}
\newcommand{\wbrif}[1]{\msf{br\_if}~{#1}}
\newcommand{\wreturn}{\msf{return}}
\newcommand{\wcall}[1]{\msf{call}~{#1}}
\newcommand{\wlabel}[2]{\msf{label}~\{#1\}~{#2}}
\newcommand{\wframe}[2]{\msf{frame}~({#1}, {#2})}
\newcommand{\wtrapping}{\msf{trapping}}
\newcommand{\wbreaking}[1]{\msf{breaking}~{#1}}
\newcommand{\wreturning}[1]{\msf{returning}~{#1}}
\newcommand{\wconfig}[5]{\{\msf{module}{:}~{#1};~\msf{mem}{:}~{#2};~\msf{locals}{:}~{#3};~\msf{stack}{:}~{#4};~\msf{instrs}{:}~{#5}\}}
\newcommand{\wfunc}[4]{\{\msf{params}{:}~{#1};~\msf{locals}{:}~{#2};~\msf{return}~{#3};~\msf{body}{:}~{#4}\}}
\newcommand{\wmodule}[1]{\{\msf{funcs}{:}~{#1}\}}
\newcommand{\wcg}{\msf{globals}}
\newcommand{\wcf}{\msf{funcs}}
\newcommand{\wci}{\msf{instrs}}
\newcommand{\wcs}{\msf{stack}}
\newcommand{\wcl}{\msf{locals}}
\newcommand{\wcm}{\msf{mem}}
\newcommand{\wcmod}{\msf{module}}
\newcommand{\wsteps}[2]{\steps{\brc{#1}}{\brc{#2}}}
\newcommand{\with}{\underline{\msf{with}}}
\newcommand{\wvalid}[2]{{#1} \vdash {#2}~\msf{valid}}
% assign4.3 custom
\newcommand{\wtry}[2]{\msf{try}~{#1}~\msf{catch}~{#2}}
\newcommand{\wraise}{\msf{raise}}
\newcommand{\wraising}[1]{\msf{raising}~{#1}}
\newcommand{\wif}[2]{\msf{if}~{#1}~{\msf{else}}~{#2}}
\newcommand{\wfor}[4]{\msf{for}~(\msf{init}~{#1})~(\msf{cond}~{#2})~(\msf{post}~{#3})~{#4}}
\newcommand{\windirect}[1]{\msf{call\_indirect}~{#1}}
% session types
\newcommand{\ssend}[2]{\msf{send}~{#1};~{#2}}
\newcommand{\srecv}[2]{\msf{recv}~{#1};~{#2}}
\newcommand{\soffer}[4]{\msf{offer}~\{{#1}\colon({#2})\mid{#3}\colon({#4})\}}
\newcommand{\schoose}[4]{\msf{choose}~\{{#1}\colon({#2})\mid{#3}\colon({#4})\}}
\newcommand{\srec}[1]{\msf{label};~{#1}}
\newcommand{\sgoto}[1]{\msf{goto}~{#1}}
\newcommand{\dual}[1]{\overline{#1}}
% Inference rules
\newcommand{\inferrule}[3][]{\cfrac{#2}{#3}\;{#1}}
\newcommand{\ir}[3]{\inferrule[\text{(#1)}]{#2}{#3}}
\newcommand{\s}{\hspace{1em}}
\newcommand{\nl}{\\[2em]}
\newcommand{\evalto}{\boldsymbol{\overset{*}{\mapsto}}}
\newcommand{\steps}[2]{#1 \boldsymbol{\mapsto} #2}
\newcommand{\evals}[2]{#1 \evalto #2}
\newcommand{\subst}[3]{[#1 \rightarrow #2] ~ #3}
\newcommand{\dynJ}[2]{#1 \proves #2}
\newcommand{\dynJC}[1]{\dynJ{\ctx}{#1}}
\newcommand{\typeJ}[3]{#1 \proves \hasType{#2}{#3}}
\newcommand{\typeJC}[2]{\typeJ{\ctx}{#1}{#2}}
\newcommand{\hasType}[2]{#1 : #2}
\newcommand{\val}[1]{#1~\msf{val}}
\newcommand{\num}[1]{\msf{Int}(#1)}
\newcommand{\err}[1]{#1~\msf{err}}
\newcommand{\trans}[2]{#1 \leadsto #2}
\newcommand{\size}[1]{\left|#1\right|}
$$
Digest - March 2017
Will Crichton
—
March 30, 2017
This is the start of a series about highlighting cool events, people, games, etc. that happened recently or I encountered recently and don't need their own blog post. I'll try to keep this up at least every two months!
Book: Timescape (★★★☆☆)
Timescape details a world imperiled by rapid climate change caused by dangerous fertilizers inadvertently causing a biochemical chain reaction in the ocean. The world appears to be on the brink of collapse, so a set of scientists try to send messages back in time to prevent the catastrophe from ever occurring. The book is fairly famous, winning the Nebula award for science fiction writing back in 1992. I always enjoy doomsday scenario entertainment, and this book was no exception. It does a good job of depicting a crumbling world in a more believable way than your normal zombie apocalypse. However, I found the book goes into a LOT of technical detail on the mechanics of the time travel and not in a particularly illuminating way. Most of the explanations felt pseudo-sciency, but that they were trying hard to not to seem like pseudo-science. Subsequently, there’s a lot of pages in this book when I feel it could be half as long for the same story. I would give it another half a star if such a unicode character exists, but in the meantime, 3 stars.
Movie: Logan (★★★★☆)
Logan follows Wolverine through his final chapter (with Hugh Jackman, at leasts) as he tries to rescue a young mutant in a slightly-futuristic world with few mutants left. Props to the cinematographers, make-up artists, and Hugh Jackman for really bringing out the gritty, grizzled essence of both the lead and his story. The movie shines in its character development since it has more time to spend individually on the important people instead of splitting it across 35 different X-Men. It also doesn’t try to play up the dramatic moments with sweeping orchestras or majestic environments, and instead keeps the shots and the pacing short and sweet. The movie is still fairly predictable and the “making kids in a lab” trope is getting a little old (see: Stranger Things), but overall better than most superhero movies we’re seeing these days.
Game: Subnautica (★★☆☆☆)
Subnautica is basically underwater Minecraft with more of a plotline. You’re stranded in the middle of the ocean on a deserted planet (or is it…….?) after your ship crash lands. Inevitably you’re the only survivor since NPCs are hard to make, and the game focuses on exploring your surroundings, fighting off underwater creatures, finding survival elements (food/water), and ultimately building items, ships, and a full-on seabase as you progress through the story. To be clear: this game is awesome, I loved most of the time I played it, and it has a lot of potential. I absolutely love exploring games in this genre, and Subnautica isn’t procedurally generated so the map is actually interesting (see: No Man’s Sky). Why two stars? The game shuts down after about 15 hours. Yes, it’s still in the early release, but that’s no excuse to be completely broken. Basically as more animals/environment cruft continue to spawn, the game gets slower and slower until it grinds to a screeching halt. I will happily give this a 5 star rating once that’s, but until then, 2 stars.
Technology: Gene drives
You may have heard of CRISPR, a new tool that can edit genes both precisely and cheaply, enabling gene modification on a scale unlike anything seen before. CRISPR on its own is a huge topic with a lot of ramifications—now, for low cost and with high accuracy, we can take any organism and just snip its genes to be whatever we want it to be. GMOs, designer babies, you name it. (We still have to know which genes to snip, though.) A problem with CRISPR is that it’s difficult to ensure that modified genes are passed from parent to child. For example, if you CRISPR’d a mosquito such that it could no longer carry malaria and released it into the wild, it might produce a few offspring with the same anti-malaria gene, but likely the gene would die out in a few generations.
The solution to this is called a gene drive: instead of relying on natural hereditary mechanics (think Mendel and pea pods), we can use CRISPR to encode not just the target gene, e.g. anti-malaria, but also to embed the CRISPR machinery itself inside the target organism. Most organisms (unless you’re a bacteria) do not have innate CRISPR abilities, but we change that using CRISPR. So a mosquito could pass to its child not just the anti-malaria gene, but a CRISPR gene drive that will make 100% sure the child has the anti-malaria gene by inserting it if it does not get naturally inherited. For populations that breed rapidly and fly like mosquitos, releasing a single gene-drive-equipped organism into the wild could cause the gene to spread to the entire world’s population within months.
As a computer scientist, I find this fascinating. Gene drives allow us to insert essentially metaprogramming machinery into organisms that propagates across generations. I’m reminded of Ted Chiang’s short story Understand where a drug treatment enables a superintelligent user to metaprogram his own brain. Of course, as a human being, I find this utterly terrifying. Not just because of the potential gene autocracy waiting to be imposed, but also by the fact that anyone can do this. CRISPR is cheap and easy, so a single deranged biologist could decide the fate of an entire species, or potentially the global ecosystem. This is a technology which both individuals and governments alike need to heavily regulate and secure.
YouTube channel: Todd in the Shadows
Todd in the Shadows does critical reviews of pop songs. The reviews themselves are engaging and often provide a new perspective on a song or generally on criteria for evaluating popular music that I haven’t considered before.
Song: Wolf - Skott
Soaring vocals and super catchy hook. Love the artist and hope to see more from her soon.
Food: Sushirritos
Try it the next time you’re in SF. The best kind of fusion.
Podcast: 慢速中文 Slow Chinese
A podcast dedicated to discussing everyday topics in Chinese at a pace understandable to learners. Highly recommended!