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.
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.
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.
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]