diff options
| -rw-r--r-- | doc/ref/api-macros.texi | 29 |
1 files changed, 18 insertions, 11 deletions
diff --git a/doc/ref/api-macros.texi b/doc/ref/api-macros.texi index cdb33df31..a353719cb 100644 --- a/doc/ref/api-macros.texi +++ b/doc/ref/api-macros.texi @@ -63,7 +63,7 @@ transformers, consider the following example macro definition: (begin exp ...))))) (when #t - (display "hey ho\n") + (display "hey ho\n") (display "let's go\n")) @print{} hey ho @print{} let's go @@ -87,7 +87,7 @@ One can also establish local syntactic bindings with @code{let-syntax}. Bind each @var{keyword} to its corresponding @var{transformer} while expanding @var{exp1} @var{exp2} @enddots{}. -A @code{let-syntax} binding only exists at expansion-time. +A @code{let-syntax} binding only exists at expansion-time. @example (let-syntax ((unless @@ -1236,14 +1236,19 @@ But if a syntactic definition needs to call out to a normal procedure at expansion-time, it might well need need special declarations to indicate that the procedure should be made available at expansion-time. -For example, the following code will work at a REPL, but not in a file: +For example, the following code tries to embed a compilation +timestamp in the compiled bytecode using a macro that expands +to the date as a string literal. It will work at a REPL, but +not in a file, as it cannot be byte-compiled: @example -;; incorrect (use-modules (srfi srfi-19)) -(define (date) (date->string (current-date))) -(define-syntax %date (identifier-syntax (date))) -(define *compilation-date* %date) +(define start-date (date->string (current-date))) +(define-syntax *compilation-date* + (lambda (sintax) + start-date)) +(display *compilation-date*) +(newline) @end example It works at a REPL because the expressions are evaluated one-by-one, in order, @@ -1253,12 +1258,14 @@ evaluated until the compiled file is loaded. The fix is to use @code{eval-when}. @example -;; correct: using eval-when (use-modules (srfi srfi-19)) (eval-when (expand load eval) - (define (date) (date->string (current-date)))) -(define-syntax %date (identifier-syntax (date))) -(define *compilation-date* %date) + (define start-date (date->string (current-date)))) +(define-syntax *compilation-date* + (lambda (sintax) + start-date)) +(display *compilation-date*) +(newline) @end example @deffn {Syntax} eval-when conditions exp... |