defmacro

The last obstacle is learning about defmacro and quasiquote/unquote, but that's easy once you're comfortable with lists and iteration.

Check out this recursive implementation of shift, which is like Common Lisp's shiftf: (defmacro shift (:env env.

The simplest mechanism is just to pass the macro on to another macro: (defmacro if-match [pat expr then else] (if (list?

TXR Lisp: @(do (macro-time (defun abc-proc (n) ^(defun,n () (pprinl ',n)))) (defmacro abc-procs (.

However, most schemes have a library that adds your traditional defmacro style macros, CL users are likely to want, but there use is almost always discouraged.

This is also why you don't simply use something like `defmacro` that will not let you supply syntactic information (syntax objects) with location and context information.

But I can also define: (defmacro foo [x]:foo) which always returns a keyword.

That's definitely true in terms of defmacro and syntax-case.

YC + all of YC's internal applications, there are 738 calls to def (= CL defun) and 187 calls to mac (= CL defmacro).

Years ago at a standards meeting (well, having drinks, not during the meeting itself) he and I were talking about C++ and Lisp and I said how much I missed defmacro.

Trivial test: macro-error-test.tl: 1: (defmacro mac (expr) 2: expr) 3: (mac (/ 1 0)) $ txr macro-error-test.tl txr: unhandled exception of type numeric-error: txr: possibly triggered at macro-error-test.tl:3 by form (/ 1 0) txr: message: /: division by zero If we change the example to this: 1: (defmacro mac (expr) 2: (copy expr)) 3: (mac (/ 1 0)) the error is exactly the same.

For example, this 3-liner would get you the "multiple array unpacking" in clojure: (defmacro pep448 [f & args] (let [unpack?

This is how Clojure actually implements "or": (defmacro or "Evaluates exprs one at a time, from left to right.

The definition syntax looks just like a method definition, except it's "defmacro" instead of "def", and the macro body receives an AST instead of (or in addition to) your usual arguments.

This actually isn't an issue most of the time; since functions' APIs vary so much already (arity, return values, types, etc.) (defmacro unless (condition branch) `(if,condition nil,branch));; Works (unless keep (delete-file "foo.txt")) - Do everything with syntax rewriting!