I strongly disagree. First, it's possible that reading "Tree" is harder than reading "T", but that doesn't mean that the time needed to understand an expression

I strongly disagree. First, it's possible that reading "Tree" is harder than reading "T", but that doesn't mean that the time needed to understand an expression composed from Ts is shorter than the time to understand Trees. I think - I have no proof, but so you don't for the contrary claim - that the time needed to decipher the meaning of abbreviated variable is greater than short variables save. As for the type system - I like it strong, static and abstract. It's true that defining GADT happens on a level so high, that some of the type parameters can stand for literally anything, and naming them something other than "a" or "x" or "o" would be silly. That doesn't mean that the type system makes you abbreviate every single name used in definitions. The same goes for overusing infix functions. In Haskell this seems to be a cultural thing: in OCaml, for example, while signatures are really terse, the types, types constructors, etc. are named (almost) always with full words. The same happens in Scheme, or more exactly in Typed Racket, where lack of syntactic support means that you need more letters to be able to easily decipher the meaning. In Erlang, where they use "success typing" as an add-on to the language, this too holds true. There is that language, J - descendant of APL. I actually went and learned some of it. Now, J is a mathematical notation and while it is quite nice as far as array languages go, it is hardly the best general purpose language. Probably because it's a mathematical notation. Yet even in J, functions other than the core vocabulary are named with full words. Sometimes with a few words. I have nothing against maths or Haskell. What I want to say is that over-shortening everything is a sign of elitist behavior, which is reinforced by the community, and which serves no useful purpose, and that there are communities gathered around Haskell alternatives which were able to mitigate this problem. As long as no one provides me with a proof that overusing shortened to 2 characters names is beneficial to the readers program understanding, I think I won't change my mind.