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The expressibility of a language is what can be expressed in it, not what it can express to you. This additional feature allows you to express this projection w

The expressibility of a language is what can be expressed in it, not what it can express to you. This additional feature allows you to express this projection without being explicit.

jeffbee 2y ago
I disagree. Any language can tell the computer what to do. The quality of a good language is that it also clearly communicates to human readers.
- rileymat2 2y ago
  I think expressiblity is trickier than that. You can think in a language with an imperative mindset where you are describing what to do, or another with a declarative mindset.
- justinpombrio 2y ago
  That's true, but unrelated to the common usage of the word "expressiveness" when talking about programming languages. There's often a tradeoff between expressiveness and the thing you're talking about, which I'll call clarity. For example, macros increase expressiveness but decrease clarity. In Racket (or other lisps), you can define a macro `(my-let x 17 (+ x 1)) -> 18`. This is expressive, as most other languages don't let you define binding constructs so easily, but also bad for clarity because `my-let` doesn't look different than a regular function, so it's hard to tell at a glance that it's doing something a function could never do.
- dcsommer 2y ago
  I think you are thinking of the concept of "explicitness" not "expressiveness".
- soegaard 2y ago
  "On the expressive power of programming languages" Matthias Felleisen https://jgbm.github.io/eecs762f19/papers/felleisen.pdf https://jgbm.github.io/eecs762f19/papers/felleisen.pdf Abstract The literature on programming languages contains an abundance of informal claims on the relative expressive power of programming languages, but there is no framework for formalizing such statements nor for deriving interesting consequences. As a first step in this direction, we develop a formal notion of expressiveness and investigate its properties. To validate the theory, we analyze some widely held beliefs about the expressive power of several extensions of functional languages. Based on these results, we believe that our system correctly captures many of the informal ideas on expressiveness, and that it constitutes a foundation for further research in this direction.

The expressibility of a language is what can be expressed in it, not what it can express to you. This additional feature allows you to express this projection without being explicit.

jeffbee 2y ago

I disagree. Any language can tell the computer what to do. The quality of a good language is that it also clearly communicates to human readers.

rileymat2 2y ago
I think expressiblity is trickier than that. You can think in a language with an imperative mindset where you are describing what to do, or another with a declarative mindset.
justinpombrio 2y ago
That's true, but unrelated to the common usage of the word "expressiveness" when talking about programming languages. There's often a tradeoff between expressiveness and the thing you're talking about, which I'll call clarity. For example, macros increase expressiveness but decrease clarity. In Racket (or other lisps), you can define a macro `(my-let x 17 (+ x 1)) -> 18`. This is expressive, as most other languages don't let you define binding constructs so easily, but also bad for clarity because `my-let` doesn't look different than a regular function, so it's hard to tell at a glance that it's doing something a function could never do.
dcsommer 2y ago
I think you are thinking of the concept of "explicitness" not "expressiveness".
soegaard 2y ago
"On the expressive power of programming languages" Matthias Felleisen https://jgbm.github.io/eecs762f19/papers/felleisen.pdf https://jgbm.github.io/eecs762f19/papers/felleisen.pdf Abstract The literature on programming languages contains an abundance of informal claims on the relative expressive power of programming languages, but there is no framework for formalizing such statements nor for deriving interesting consequences. As a first step in this direction, we develop a formal notion of expressiveness and investigate its properties. To validate the theory, we analyze some widely held beliefs about the expressive power of several extensions of functional languages. Based on these results, we believe that our system correctly captures many of the informal ideas on expressiveness, and that it constitutes a foundation for further research in this direction.