A higher order function doesn't serve the same purpose as a macro. A higher order function is meant to be applied, called, composed etc. A lisp macro is a different type of abstraction. For example, many people think that macros are just hiding lambda's of higher order functions. This is wrong. A macro abstracts over implementation details of a construct to make it read naturally. For example, you can write a function that opens and then closes a file like so...

  with-open-file(filename, lambda file: do stuff with file)

but with a lisp macro, you only have to write

  with-open-file (filename):
     do stuff with file

The point of an abstraction is so you don't have to think about the implementation. Written like the latter, with-open-file is simply more natural to write this way. You only have to think, "oh, its a construct that opens a file then closes it after the body is done", rather than "oh, its a higher order function that i have to pass another function into that takes the file as an argument..." etc.

When you write with-open-file as a macro, it could be implemented as a higher order function, or it could be implemented as a low level set of GOTO statements. It doesn't matter. The macro abstracts away the low level detail, just providing the most natural way for you to use the construct. It might not seem like the macro is doing much in that particular example, but a construct that defines a class (like defclass) is something you can write as a macro, which can expand into functions that do the actual defining. You could write a class defining construct as a higher order function, but then you'd have to constantly worry about how your construct was implemented as a function. instead of just writing something natural like

  defclass tiger (animal):
    age init-value: 0
    name type: string

which you could write if you implemented defclass as a macro. otherwise, you'd have to do something crazy stupid like

  defclass(name='tiger', inherits-from = find-class('animal')
           slots=['age, name'] ...)

how could a higher order function possibly implement that without making people using it tear their hair out? They have to bend to the implementation, not make the abstraction bend to what's natural.

user:	chaoky
created:	August 22, 2014
karma:	106