;; Copyright 2007-2011, Matthew Welland.
;;
;; This program is made available under the GNU GPL version 2.0 or
;; greater. See the accompanying file COPYING for details.
;;
;; This program is distributed WITHOUT ANY WARRANTY; without even the
;; implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
;; PURPOSE.
;;
;;======================================================================
;; Sugar
;;======================================================================
;;
;; (require 'syntax-case)
;;
;; (define-syntax s:if-param
;; (syntax-rules ()
;; [(_ s x) (if (s:get s) x (s:comment "s:if not"))]
;; [(_ s x y) (if (s:get s) x y)]))
;; ;;
;; (define-syntax s:if-test
;; (syntax-rules ()
;; [(_ s x) (if (string=? "yep" s) x (list "s:if not"))]
;; [(_ s x y) (if (string=? "yep" s) x y)]))
;; Some of these routines use:
;;
;; http://www.cs.toronto.edu/~gfb/scheme/simple-macros.html
;;
;; Syntax for defining macros in a simple style similar to function definiton,
;; when there is a single pattern for the argument list and there are no keywords.
;;
;; (define-simple-syntax (name arg ...) body ...)
;;
(define-syntax define-simple-syntax
(syntax-rules ()
((_ (name arg ...) body ...)
(define-syntax name (syntax-rules () ((name arg ...) (begin body ...)))))))
;;======================================================================
;; syntatic sugar items
;;======================================================================
;; We often seem to want to include stuff if a conditional is met
;; otherwise not include it. This routine makes that slightly cleaner
;; since using a pure if results in #<undefined> objects. (admittedly they
;; should be ignored but this is slightly cleaner I think).
;;
;; NOTE: This has to be a macro or the true clause will be evaluated
;; whether "a" is true or false
;; If a is true return b, else return '()
(define-simple-syntax (s:if a b)
(if a b '()))
;; Using the Simple-Syntax System
;;
;; The syntax for defining macros in this system is similar to that for defining functions. In fact if the macro has a fixed number of arguments the syntax is identical. For example:
;;
;; ; Define a simple macro to add a value to a variable.
;; ;
;; (define-simple-syntax (+= variable value)
;; (set! variable (+ variable value)))
;;
;; ; Use it.
;; ;
;; (define v 2)
;; (+= v 7)
;; v ; => 9
;;
;; For a fixed number of arguments followed by an unknown number of arguments we use ... after a single argument to represent the unknown number (possibly zero) of arguments. For example, let's revise our definition of += to allow zero or more values to be added:
;;
;; ; Define a simple macro to add a zero or more values to a variable
;; ;
;; (define-simple-syntax (+= variable value ...)
;; (set! variable (+ variable value ...)))
;;
;; ; Use it
;; ;
;; (define v 2)
;; (+= v 7)
;; v ; => 9
;; (+= v 3 4)
;; v ; => 16
;; (+= v)
;; v ; => 16
;;
;; (define-macro (s:if-param varname . dat)
;; (match dat
;; (() '())
;; ((a) `(if (s:get ,varname) ,a '()))
;; ((a b) `(if (s:get ,varname) ,a ,b))))
;;
;; (define-macro (s:if-sessionvar varname . dat)
;; (match dat
;; (() '())
;; ((a) `(if (s:session-var-get ,varname) ,a '()))
;; ((a b) `(if (s:session-var-get ,varname) ,a ,b))))
;;