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> But I might have to create new language features just to get anything done in Lisp. One example is LOOP. LOOP is a standard part of Common Lisp, so whatever

by gjm11 13y ago

> But I might have to create new language features just to get anything done in Lisp. One example is LOOP. LOOP is a standard part of Common Lisp, so whatever it is it can't be an example of how Lisp-as-it-comes isn't good enough and you need macros to bring it up to standard. > Now, does LOOP do more than a C-style for or while loop? I doubt it In the sense in which a C-style for or while loop doesn't do more than goto, you're correct. Otherwise, of course you're incorrect; LOOP does a lot more than for and while do. (Random example: (loop for i from 1 to 10 collect (* i i)) makes a list of squares. No instance of C's for or while does anything like this.) > Lisp needs macros to be usable. I'm not convinced that C does. Could you give an example of something that C lets you do "out of the box", that Lisp (let's say specifically Common Lisp) doesn't, but that Lisp could be made to do using macros? I don't think I can think of any; there are things you can do better in C than in Lisp (e.g., close-to-the-metal bit-twiddling, or interfacing with other things written in C) but they don't have anything to do with macros.

AnimalMuppet 13y ago
LOOP is a macro, right? It's a standard macro, sure. But the point isn't standard vs. non-standard, the point is macro vs. non-macro. Without any macros, Lisp can't do loops very well. That's my point - Lisp without macros isn't very useful. >Random example: (loop for i from 1 to 10 collect (* i i)) makes a list of squares. No instance of C's for or while does anything like this. for (int i = 1; i <= 10; i++) list.push_back(i * i); Yeah, it's C++ using STL rather than straight C. (I suppose you could argue that C lacks a list type and therefore isn't very useful... but I could create a linked-list struct and write a push_back function. For that matter, I could just have int list[11]; for (int i = 0; i <= 10; i++) list[i] = i * i; I don't really think that list-vs-array is really relevant to the relative power of the loops in C and Lisp.) > Could you give an example of something that C lets you do "out of the box", that Lisp (let's say specifically Common Lisp) doesn't, but that Lisp could be made to do using macros? Well, macros produce Lisp code, so there is nothing that you can write in a macro that you cannot write in straight Lisp. But in non-macro Lisp, loops are really painful to write - the LOOP macro is part of the standard for a reason.
- gjm11 13y ago
  > But the point isn't standard vs. non-standard, the point is macro vs. non-macro. But why? Imagine an alternate world in which all the things in the Common Lisp standard that are currently defined to be macros are special forms instead. I claim that (1) in that world, the criticism you're making would not apply, and (2) that world's Common Lisp is (a) not better in any way than our world's and (b) actually slightly worse, because code-walking macros would be more painful to write. Doesn't that indicate that there's something wrong with your criticism? What I'm not seeing is how the fact that some standard features of Common Lisp are defined to be implemented via macros is a weakness, which you seem to be arguing it is. On LOOP: Sure, you can use a C for loop to build a list of squares (but, note, it doesn't in fact do the same thing as the Lisp code and couldn't possibly, because (1) the Lisp code is an expression and a for loop is a statement but not an expression, and (2) that invocation of LOOP makes a new list and returns its final value rather than appending to some specific list that's already been created as your kinda-sorta-parallel code does). But that's what I meant about goto. You can use goto to do what a C for loop does. If you wouldn't say "Does for do more than goto? I doubt it" then you shouldn't say "Does LOOP do more than for? I doubt it". > But in non-macro Lisp, loops are really painful to write But "non-macro Lisp", if by that you mean something like "Common Lisp, with all the features defined to be implemented as macros taken out", is a thing that doesn't exist and that never would exist. (If for some reason you were implementing a Lisp without macros, and if you actually intended it to be a good general-purpose language, then of course you would include some decent looping facilities.) So this is not an example of something that Lisp doesn't let you do "out of the box"; LOOP is right there in the box. As you say, LOOP is part of the standard for a reason.
  - AnimalMuppet 13y ago
    Well, my initial claim was that Lisp needs macros in a way that C/C++ doesn't. You are now stating that Lisp could have been written in a way that it didn't need macros to be usable. And you're right, it could have been. But I don't think that that's the point. The point is not that implementing things as macros is a weakness. It's that the language (as written) needs those macros. And C, as written, does not. But I suppose from your point of view, my argument is a distinction without a difference...

by gjm11 13y ago

AnimalMuppet 13y ago

LOOP is a macro, right? It's a standard macro, sure. But the point isn't standard vs. non-standard, the point is macro vs. non-macro. Without any macros, Lisp can't do loops very well. That's my point - Lisp without macros isn't very useful. >Random example: (loop for i from 1 to 10 collect (* i i)) makes a list of squares. No instance of C's for or while does anything like this. for (int i = 1; i <= 10; i++) list.push_back(i * i); Yeah, it's C++ using STL rather than straight C. (I suppose you could argue that C lacks a list type and therefore isn't very useful... but I could create a linked-list struct and write a push_back function. For that matter, I could just have int list[11]; for (int i = 0; i <= 10; i++) list[i] = i * i; I don't really think that list-vs-array is really relevant to the relative power of the loops in C and Lisp.) > Could you give an example of something that C lets you do "out of the box", that Lisp (let's say specifically Common Lisp) doesn't, but that Lisp could be made to do using macros? Well, macros produce Lisp code, so there is nothing that you can write in a macro that you cannot write in straight Lisp. But in non-macro Lisp, loops are really painful to write - the LOOP macro is part of the standard for a reason.

gjm11 13y ago
> But the point isn't standard vs. non-standard, the point is macro vs. non-macro. But why? Imagine an alternate world in which all the things in the Common Lisp standard that are currently defined to be macros are special forms instead. I claim that (1) in that world, the criticism you're making would not apply, and (2) that world's Common Lisp is (a) not better in any way than our world's and (b) actually slightly worse, because code-walking macros would be more painful to write. Doesn't that indicate that there's something wrong with your criticism? What I'm not seeing is how the fact that some standard features of Common Lisp are defined to be implemented via macros is a weakness, which you seem to be arguing it is. On LOOP: Sure, you can use a C for loop to build a list of squares (but, note, it doesn't in fact do the same thing as the Lisp code and couldn't possibly, because (1) the Lisp code is an expression and a for loop is a statement but not an expression, and (2) that invocation of LOOP makes a new list and returns its final value rather than appending to some specific list that's already been created as your kinda-sorta-parallel code does). But that's what I meant about goto. You can use goto to do what a C for loop does. If you wouldn't say "Does for do more than goto? I doubt it" then you shouldn't say "Does LOOP do more than for? I doubt it". > But in non-macro Lisp, loops are really painful to write But "non-macro Lisp", if by that you mean something like "Common Lisp, with all the features defined to be implemented as macros taken out", is a thing that doesn't exist and that never would exist. (If for some reason you were implementing a Lisp without macros, and if you actually intended it to be a good general-purpose language, then of course you would include some decent looping facilities.) So this is not an example of something that Lisp doesn't let you do "out of the box"; LOOP is right there in the box. As you say, LOOP is part of the standard for a reason.
- AnimalMuppet 13y ago
  Well, my initial claim was that Lisp needs macros in a way that C/C++ doesn't. You are now stating that Lisp could have been written in a way that it didn't need macros to be usable. And you're right, it could have been. But I don't think that that's the point. The point is not that implementing things as macros is a weakness. It's that the language (as written) needs those macros. And C, as written, does not. But I suppose from your point of view, my argument is a distinction without a difference...