Explanation of macros; Haskell macros

[Marcin 'Qrczak' Kowalczyk]

On Thu, 30 Oct 2003 23:29:00 +0000, Peter Seibel wrote:

>> Yes, but the point is that with a concise syntax for lambda, entire
>> classes of macros can become unnecessary. That's how Smalltalk
>> handles 'if', for example - no macros or special forms needed.
> 
> Okay, so I picked an unfortunate example in that it also falls in the
> class of macros that become unecessary when other bits of syntactic
> sugar are provided. How about this one.
[...]

Nobody says that *everything* should be expressed by higher order
functions. But with enough builtin syntax and concise anonymous function
notation (in particular using {} or [] for functions without arguments)
there are much fewer uses of macros than in Lisp, which has little builtin
syntax and ugly anonymous functions.

The remaining uses of macros are so rare that few languages choose to take
the cost of having macros (I mean full-blown Lisp-like macros which execute
arbitrary code at compile time and can examine its parameters).

The costs: syntax seems to be constrained to have a very regular surface
structure full of parentheses; the language must describe and implement a
representation of code as data which would otherwise be unnecessary; every
compiler must include an interpreter; it's hard to report errors to the
user showing the code as it's written in the source if the error is found
after macro expansion.

I'm not saying that the cost is obviously too high but that it's a
tradeoff, macros don't come for free. And that there are other ideas which
can replace many macros with different tradeoffs: namely a richer builtin
syntax and concise anonymous functions. In a lazy language there are yet
fewer uses of macros.

-- 
   __("<         Marcin Kowalczyk
   \__/       qrczak at knm.org.pl
    ^^     http://qrnik.knm.org.pl/~qrczak/