← Back to context

Comment by lmm

6 days ago

> Best I can tell, all usable definitions surrounding "Command" seem to suggest an associated action, which isn't true of all statements in imperative programming.

The defining characteristic of a programming "statement" is that it can perform some action (even if not all of them do), whereas statements in the usual everyday sense are inert. So it's not a good term.

11 comments

lmm

Reply
9rx  5 days ago

> The defining characteristic of a programming "statement" is that it can perform some action

Given a declaration "statement" such as:

     int x;

What is the expected action? Memory allocation... I guess? Does any compiler implementation actually do that? I believe, in the age of type systems being all the rage, one would simply see that as a type constraint, not as a command to act upon.

Expressing an idea (the values used henceforth should be integers) seems more applicable, no?

  • lmm  5 days ago

    > Given a declaration "statement" such as:

    > int x;

    > What is the expected action?

    In a language that requires you to declare variables before you use them, it clearly does something - you couldn't do "x = 5;" before, and now you can. If you're trying to understand the program operationally (and if you're not then why are you thinking about statements?) it means something like "create a variable called x", even if the implementation of that is a no-op at the machine code level.

    > I believe, in the age of type systems being all the rage, one would simply see that as a type constraint, not as a command to act upon.

    But in that case by definition one would not be seeing it as a statement! Honestly to me it doesn't really matter whether "int x;" is an expression, a statement, or some mysterious third thing (in the same way that e.g. forward declaring a function isn't a statement or an expression). When we're talking about the distinction between statements and expressions we're talking primarily about statements like "x = x + 1;", which really can't be understood as a statement in the everyday English sense.

    > Memory allocation... I guess? Does any compiler implementation actually do that?

    Toy/research or embedded compilers do yes.