A dictionary of single-letter variable names
jackkelly.name
jackkelly.name
The first place I worked had a soft-but-hard rule (enforced by ridicule) that single-letter variable names not be used. Loop counters like i, j, and k were frowned upon. However, counters like ii, jj, and kk were fine for matrix operations, xx and yy for image loops, etc.
There were a couple of key guidelines to follow:
1. If it can have more meaning than sample, pixel, or matrix position, give it more meaning, but two characters repeated is fine for loop counters (again, with meaning).
2. Whatever you use should be quickly findable with text search tools of the era (the late ‘90’s).
Someone shouldn’t have to use source inspection assistive coding tools to parse the code you write. When someone else (or you, in a few months) comes upon this code and needs to understand it, they should be able to use find to do it.
I may understand that instead of x,y it may be better to use px,py for positions and vx,vy for speed. Perhaps xx,xy for position. But I'd never use yy.
Searching for `i' requires learning the local editor's way of marking word boundaries, otherwise it'll highlight every instance of the letter `i' which is useless.
Searching for `ii' has less noise because very few words have that sequence in them, and `jj' is even rarer.
Or you can make your life easier, and use tools which helps you.
Once again, regardless of codebase.
So then you get back to the LSP question -- but for larger codebases I can tell you, those don't always work as well as you'd hope. I don't use 'ii' but it's admittedly much easier to just `rg` for variables than hope my editor plugin decides to work today.
Whatever the case, is it really that hard to use a two-letter loop counter? Try it sometime. When building at scale, it just makes sense to be considerate of diversity and do the little things to that make life easier for others.
It's not inconsiderate, we are doing a job. If you can't do your job, you don't have place in my team. And properly using an IDE is definitely part of the job. What are you using that can't open web VSCode that has all these features?
You click a button and get a web browser based IDE where you have everything ready, connected to a cloud computer with a full dev env that mirrors our prod env; that from any branch and the button is right there in pull request UI. There is no reason why someone in this org should require everyone to write double letter iterator var names just because they couldn't be bothered to play the video where I taught how to use the advanced code search and the feature could be available to them in less than a minute of fooling around if they tried.
On this scale, following standards is absolutely necessary. If my engineer has to stop and think "but wait, in this company they do it differently" - this times 150 people I currently manage - then I failed at my job.
Some devs hated me when I came into this (much smaller back then) company few years ago and the first step I did was to put a global linter and formatter there. They were angry about how they would format it better than the formatter. Well that's nice - but that doesn't scale to hundreds of people. People make mistakes, stop caring, have different opinions... And all these questions in their minds are again my failure at my job. It's my job to answer these once and forever and to make it easy to follow the rule.
While this is a personal anecdote, I was a large corporate principal engineer for many years and I am mirroring what I saw working there. I can't say this approach to making software engineering work at scale is uncommon.
Please note that here I'm talking about working at a job, usually for very good money. Nothing of this applies to personal projects, most open source projects and so on. In these cases I'm very much on your side.
Some editors like Kate highlight whole words by just selecting them (and it will not highlight letters in words). Some also do that just by placing the cursor on a word.
This is kind of basic stuff that was around in the 90s, possibly even 80s.
Some software, such as Matlab, have those letters reserved for the common case of imaginary roots of a polynomial, and “ii” and “jj” as variables is a common coding convention. Whether “i” or “j” is your letter for imaginary numbers depends on if you’re an electrical engineer or not.
If your array is named cars then you can safely assume i will be a car, but depending on the complexity of the code it just adds another step for me to parse, when I could have just named it car to begin with.
That's a simple case where the data being iterated over is clear. When the data is complex, it becomes even more useful to descriptively name i so that you can more easily see what you're working with.
A variable with big enough scope you'd be searching for it should have a full real name, no i or ii. Even when it's a loop counter, if it's present for more than a page, please tell me what you're counting.
e: event
k: key in hash map, dictionary, etc.
o: object or reflected object types
v: value in hash map, dictionary, etc.
t, u, v, w: vectors (borrowed from math)
My errors are caught as ‘e’, files are ‘f’, apparently indices are i, j, k, for as long as people been writing C.
K/V are keys and values, and, well, ‘t’ is time. I’m sure you can guess all other…
I really don’t understand how is this a specific language’s thing.
The author says as much. There's overlap for sure, but all the monad stuff, for one, is mostly Haskell-(or functional language rather)-specific.
I think the amount of polymorphic code Haskell enables means that single-letter variables are more common than in other languages (where they're usually confined to narrow scopes), and there's a lot less to say about them. Another HN commenter on this post mentioned IEnumerable<T>, which is very similar: you know nothing about T, but you need to call it _something_, and there's a common understanding in the community that you call such type variables <T>.
Haskell's typeclasses then mean you've got a lot of different concepts that could show up in a type signature, but they're still polymorphic and there's not much you _can_ say beyond "this is Foldable", or "this is a Monad". So an even broader convention has emerged.
You know that it's the type you enumerate over. I'd agree that in this case, <T> is sufficiently common language that people understand the reference (similar to how i is understood to be the index counter in a for loop), but you could definitely use a more expressive type name [1]. This becomes important if your type has two or three generic parameters.
[1] You might argue that this is more typing overhead, but your tooling will easily auto-complete it for you or refactor it after you've written the code, but before committing it. And if you don't have that type of tooling, you're in need of expressive variable names.
b is for byte or buffer
c is for character
d is for destination
e is for event or error
f is for file
g is for graph
h is for handle
i is for index
j is also for index
k is for key
l is for length
m is for mode
n is for number-of
o is for object
p is for part
q is for queue or query
r is for reader
s is for source
t is for time
u is for user
v is for value
w is for word
x is for x component
y is for y component
z is for z component
A is for array, some things in a list
B is for byte, how computers exist
C is for character, one letter in a word
D is for destination, where results are stored
E is for event, interaction in the DOM
F is for file, sometimes written to ROM
G is for graph, some edges and nodes
H is for handle, it references loads
I is for index, add 1 as time flies
J is for index, but different from i's
K is for key, in associative arrays
L is for length, as in how many j?
M is for mode, and not like ice cream
N is for count, like sheep in a dream
O is for object, some data and code
P is for part, to share out the load
Q is for queue, process one at a time
R is for reader, I can't think of a rhyme
S is for source, and you're doing great
T is for time, 429 makes you wait
U is for user, like you'll be one day
V is for value, associated to k
W is for word, collections of c
X is for x-component when doing 3D
Y is for y-component like x is again
Z is for z-component, we got to the end!
[note, i am not sure what is meant by P = part, and I know some of these are kind of lame and got worse as I got impatient to finish]
[i wrote this myself, it is not ai-written]
I remember the moment I learned that phi and theta were used by both mathematicians and physicists for rotational components of a spherical coordinates system, but that their roles are switched:
math: theta=polar phi=azimuthal
physics: phi=polar theta=azimuthal
As for phi and theta, it just seems so arbitrary.
My rule of thumb is to only use short names in the local scope of a function and have them follow conventions within the language community. Constrained like this, I see no harm in using them, since their meaning is clear within the context of their usage and there is usually no need to search for them. Of course, if the variable has a more specific meaning, I choose a more specific name.
Why the HELL would you need objects and object oriented programming? Wherever you do foo.blah(), you could just do foo_class__do_blah(obj)… so what do objects really grant you that you can’t do with basic procedural programming?
Why do you need Python’s function decorators? You can just manually copy and paste whatever logic you need into each and every function, instead of decorating them.
Why have an iterator protocol? Every datum can have it’s own bespoke way of iteration that you simply have to memorize on a case by case basis (and can not be abstracted over in any common way), why make everything conform to the same interface?
Why have anonymous functions that can close over their lexical scope (what people usually refer to as “closures”)? Consider:
let x = 0;
let inc = () => x++;
function inc(bindings) { return bindings.x++; }
I could keep going.
We have these facilities not because they are essential (go program in assembler, and you’ll see how few programming techniques and concepts your processor actually cares about), but because they are nice to have. They are nice to have because they provide us tools for abstraction, so by solving the general case, you solve a host of concrete cases.
Lenses let you abstract over data traversal and projection.
Maybe you don’t appreciate that, and that’s fine. There are C programmers who don’t mind writing 100 different hash tables for different keys and elements. If you are a Python/TS developer, I’m pretty sure you’d find that surprising — if you want a dictionary/hashtable, you just use a dict and call it done — you wouldn’t go build a new dictionary class for each and every key-type/value-type pair.
Different people have different tolerances for the drudgery of solving the same problem for the 100th time.
However: while I don’t understand why someone would choose vanilla ice cream if they’re given the option of chocolate, I wouldn’t act flabbergasted in such a scenario. Why would I? Why should I expect my desires to be the same as everyone else’s?
The only reason I can think of that someone would express shock at someone choosing vanilla over chocolate is if they think that the preference for vanilla indicates something is fundamentally wrong them. Or in other words: being a condescending bigot.
That’s kinda how you’re coming off.
In the event that you were actually asking in good faith: if you like to broaden your skills so you can finish programming work faster, I’d recommend reading up on lenses. If you don’t care about that, that’s fine too, but I’d recommend against expressing shock at the fact that others do care about these types of things.
I agree with the technical points in your post and disagree with its venom. It's important to notice patterns and abstract over them, and to teach people to spot commonalities they haven't yet noticed in their code. Next time I think you'll have better luck starting with the assumption of good faith and going from there.
Consider pair(a, b) with first(pair) and rest(pair). I can define first-lens and rest-lens for [get-first, set-first] and [get-rest, set-rest] respectively. I could use them as simple getter/setter groupings with lens-view(rest-lens, pair) or lens-set(first-lens, 4, pair), which isn't so useful by itself, or I can compose then to get third-lens with lens-compose(rest-lens, first-lens), allowing me to lens-set(third-lens, 7, pair) without a nested call.
I just tried to summarize what I could read [1] [2] [3] and I don't claim to entirely understand it, but it's still better than the sibling comment dismissing it as abstract nonsense.
[1] https://docs.racket-lang.org/lens/lens-intro.html
[2] https://hackage.haskell.org/package/lenses-0.1.4/docs/Data-L...
s - the larger data structure
a - a view value
b - a “update” value
t - the data structure after an update is applied
Of course, everything is still immutable in the same way that cons-ing a value onto a list is immutable.
The change in type between s and t allows you to nest these views, hide information, etc.
`b` and `t` are just for type-changing updates, like when you replace a field in a tuple or every element in a list.
It's a very fair question. I'm pretty sure lenses were invented because Haskell's built-in records are not ergonomic, but then the community discovered that they're extremely useful, general, and flexible.
Here is a Redux (JS) example of the problem that lenses help solve, where you are working with immutable data and want to replace one field of a deeply-nested structure: https://redux.js.org/usage/structuring-reducers/immutable-up...
You can think of a lens as a getter/setter, stored together as a first-class value. I'm not great at TS but hopefully you can see what I'm getting at with these types:
A Lens<S,T,A,B> is a pair of functions:
* get: (s: S) => A
* set: (s: S, b: B) => T
The most obvious lenses you can make are lenses that represent record fields (object properties?). But you can make lenses into other things, like a function that returns a lens into the Nth bit of an integer, or a function that takes a map key and returns a Lens from Map<K,V> to Optional<V>.
You use lenses by passing them to functions that then operate on your data. Three common ones are `view`, `set`, and `modify`:
* view: (lens: Lens<S,T,A,B>, s: S) => A
* set: (lens: Lens<S,T,A,B>, s: S, b: B) => T
* modify: (lens: Lens<S,T,A,B>, s: S, f: (a: A) => B) => T
So far, it doesn't look like we've bought much. But the real payoff comes from when you notice that lenses compose:
* compose: (outer: Lens<S,T,X,Y>, inner: Lens<X,Y,A,B>) => Lens<S,T,A,B>
This solves the "nested record problem" because you can compose the lenses for each field in the chain to get a lens from the outer structure to the field you're interested in, and functions like `set` and `modify` will correctly copy all the fields at each layer when you call `set` or `modify`. Haskell's lens libraries give you compact operators for doing this, so it all looks neat and tidy.
A reasonable response to all this machinery is, "OK, your language has bad records and you built a library to paper over them. So what?" To this I say:
1. Every language has this problem when working with nested immutable data, though not every language has the tools to compactly encode lenses and make them ergonomic to use; and
2. Lenses generalise to give you other "optics". A `Traversal<S,T,A,B>` picks out zero or more `A`s from `S`, and can replace them all with `B`s. `modify` and `set` then generalise, and perform their update on _every_ matching `A` selected by the `Traversal`, and you also get `toListOf`, which collects all matching `A`s into a list. There are other optics too, but this post is getting long.
Once you have the more powerful optics, you get a very expressive toolkit for querying and updating data, that works on any data structure that has optics defined. (And Haskell has tools to derive many optics automatically.)
Chris Penner's wonderful book, _Optics By Example_[1], has a bunch of exercises that involve slicing and dicing a big slab of Kubernetes YAML with queries like "collect a list of all 'containerPort's alongside their Pod's 'name' (from 'metadata')" and operations like "set a resource request of `memory: "256M"` for every container". The answers are extremely compact and elegant, and I don't know how you'd achieve anything similar with other methods.
I hope this helped, because there is definitely a really useful and powerful toolkit hiding behind that absurd-looking type signature.
But what optics (often sloppily referred to as lenses) give you are really powerful getters and setters. They can do what getters and setters in Python do, but they can also
- target multiple fields in multiple objects at the same time, or
- target fields only when a condition is true,
- they can target deeply nested fields,
- they can target computed values which have a compound effect on the underlying fields,
- they can return a new full object where the targeted fields are transformed by an arbitrary function, etc.
This means optics are extremely broadly useful. They can be used as OO-style getters and setters, but they can also be used to build and navigate JSON objects, or parse HTML content. It's a common interface that can be used for getting and modifying data in any broader context.
$: jQuery
_: lodash, underscore libraries
e: usually events like keyboard, button clicks, form submits, when preventing form actions...
$: querySelector
$$: querySelectorAll
It's about time js/browsers gave selectors better DX. Even simple things like reactivity and stores should be core to JS and not be up to frameworks
Note that x,y,z don’t really qualify as abbreviations since they are the full name of the component, so they can be used when the outer scope is not visible — eg as a parameter.
You are using a bad font.
https://gist.github.com/valbaca/a55cf9cdcb500e203cadc9ef3555...
Didn't they make a song about that?
a, b, c, d... e, f, g...
Something like that?
I don't Haskell, thankfully, but a lot of these are applicable broadly. Some notes/additions I've seen in other languages (but far more often these are obvious).
(only vaguely sorted, since many aren't contiguous):
a can mean "argument" particularly; also "arg"
a,b,c,d can be anything, but slightly more common for floats and/or coefficients, or matrices
a is often "array"
a can be ascii (either as string in general, or in specific)
a can be "allocator" or "allocation"
b for bytes is not shameful, but sometimes it means "buffer", "blob", or "bits" instead. Can be used for just an element or for a sequence of them.
b can be "builder" (a utility class used to construct values instead of using "new" directly)
b can be "base"
b,e for begin/end (often for iterators/indices)
c is often used for "character", "code unit", "codepoint"; ch/cu/cp can disambiguate
c can also be "constant" (either a value or a modified type)
c can also be "container"
c can also be "condition" (a boolean)
c can also be "context", but more often ctx or ctxt
d is rarely used for "data", but more often it's expanded or v is used instead
d can be "direction", but more often dir
d,s can be destination/source
e can also be "event"; ev if needed
e can also be "element" (member of an array, member of an XML-like tree)
f is common for floats (even if called "double" or "real") or fixed-point numbers
f is often file; fp/fo may be common depending on the language
g for graph
h for handle
i can also be "instruction"
i,o,r,w can be input/output
i,j,k are common as indices *or* iterators, corresponding to x, y, z if meaningful.
l is rare but can be a 4th index or iterator if needed, usually does not related to w though.
l is probably more common as "length"/"limit"
l can be "long" in various senses
l,h can be low/high, but more often lo/hi
l,r can be left,right (also lhs,rhs), especially of a binary operator (or occasionally a unary one, e.g. to disambiguate prefix/suffix)
m = mode?
n,+m are often specifically the upper bound of a range, similar to l
n can be node (of a tree/graph)
o is an arbitrary object (usually, when explicitly not a primitive or string)
o can be "origin"
p,+q are not rare as "predicate"
p,q can also be prime numbers
p is for pointer
p = part?
p,q = percent chance (often normalized to 0-1 though)
q for queue
q for query/request
q for "quad"
q,r,n,d for fractions
r (and rv/res) is sometimes used ambiguously - should it be the return value of a function I called, or the value I'm planning to return? Can also stand for "reply".
r can be "range"
r can be "rectangle"
r can be "register"
r,c for row, column; origin is top-left and axes are flipped
r,g,b,a are color components; other letters exist for other colorspaces
s is often an arbitrary string
s can also be symbol (sy/sym depending on context), statement (stmt), or set (often given a different kind of name)
s can be "stack"
t for table
t for time
t,u,v (usually uppercase) are arbitrary types in generics
u,g,o for user/group/other
v is often just an arbitrary data value (not meaningfully numeric/string/object), even without a container
v,w,t,u can also mean "vector" specifically
w = word
u,v,s,t,q are used for 2D texturing
u can be unicode
w can be wide character, but good riddance
w is for window
x can also be "expression" in particular
x,o,d,b can be hex, octal, decimal, or binary bases
x,y,w,h are start/size of a rectangle
x,y,z,w are used for 3D objects; w is often normalized to 1
_ as a function or string affix means "call gettext on this now"; N_ means "remember to call it later"
_,$ are sometimes injected as a general-utility global variable in languages with deficient standard libraries
I'm also ignoring all the various units and physical constants.
I'm pretty sure about a dozen more passed through my head while writing this but I forgot them before I finished writing the previous entry, and I can't be bothered to actually start scanning code.
b for boolean
d for distance / date
e for error / exception
f,g are often used as generic function name
g can be global value
r for radius
r is a random value
t for tally
t is any temporary value
m for matrixI thought about `M` for matrix but after thinking I realized it's almost always `A` or something, with `m` as a dimension. That does remind me of `I` for identity though ...
Ah, the editing window is closed, so I guess I have to extend it:
f,g,h - function
f - flags
i - identity (e.g. of matrix)
h,n/p,m - haystack, needle/pattern, match
h,t - head, tail
k,v - key, value of a map/dictionary
l - location
s - state
t - tokenI would say that underscore is used as convention. There are languages where the underscore is either tool supported or language reserved for this purpose broadly or in limited context (lambdas). Languages that use underscore for ignored values include Java, Erlang, Python, Scala, Clojure, F#, SML, Swift, et al.
It’s like the use of `T` as a name in most Java or C++ generics.