1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
|
;; Quasisyntax in terms of syntax-case.
;;
;; Code taken from
;; <http://www.het.brown.edu/people/andre/macros/index.html>;
;; Copyright (c) 2006 Andre van Tonder. All Rights Reserved.
;;
;; Permission is hereby granted, free of charge, to any person
;; obtaining a copy of this software and associated documentation
;; files (the "Software"), to deal in the Software without
;; restriction, including without limitation the rights to use, copy,
;; modify, merge, publish, distribute, sublicense, and/or sell copies
;; of the Software, and to permit persons to whom the Software is
;; furnished to do so, subject to the following conditions:
;;
;; The above copyright notice and this permission notice shall be
;; included in all copies or substantial portions of the Software.
;;
;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
;; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
;; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
;; NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
;; BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
;; ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
;; CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
;; SOFTWARE.
;;=========================================================
;;
;; To make nested unquote-splicing behave in a useful way,
;; the R5RS-compatible extension of quasiquote in appendix B
;; of the following paper is here ported to quasisyntax:
;;
;; Alan Bawden - Quasiquotation in Lisp
;; http://citeseer.ist.psu.edu/bawden99quasiquotation.html
;;
;; The algorithm converts a quasisyntax expression to an
;; equivalent with-syntax expression.
;; For example:
;;
;; (quasisyntax (set! #,a #,b))
;; ==> (with-syntax ((t0 a)
;; (t1 b))
;; (syntax (set! t0 t1)))
;;
;; (quasisyntax (list #,@args))
;; ==> (with-syntax (((t ...) args))
;; (syntax (list t ...)))
;;
;; Note that quasisyntax is expanded first, before any
;; ellipses act. For example:
;;
;; (quasisyntax (f ((b #,a) ...))
;; ==> (with-syntax ((t a))
;; (syntax (f ((b t) ...))))
;;
;; so that
;;
;; (let-syntax ((test-ellipses-over-unsyntax
;; (lambda (e)
;; (let ((a (syntax a)))
;; (with-syntax (((b ...) (syntax (1 2 3))))
;; (quasisyntax
;; (quote ((b #,a) ...))))))))
;; (test-ellipses-over-unsyntax))
;;
;; ==> ((1 a) (2 a) (3 a))
(define-syntax quasisyntax
(lambda (e)
;; Expand returns a list of the form
;; [template[t/e, ...] (replacement ...)]
;; Here template[t/e ...] denotes the original template
;; with unquoted expressions e replaced by fresh
;; variables t, followed by the appropriate ellipses
;; if e is also spliced.
;; The second part of the return value is the list of
;; replacements, each of the form (t e) if e is just
;; unquoted, or ((t ...) e) if e is also spliced.
;; This will be the list of bindings of the resulting
;; with-syntax expression.
(define (expand x level)
(syntax-case x (quasisyntax unsyntax unsyntax-splicing)
((quasisyntax e)
(with-syntax (((k _) x) ;; original identifier must be copied
((e* reps) (expand (syntax e) (+ level 1))))
(syntax ((k e*) reps))))
((unsyntax e)
(= level 0)
(with-syntax (((t) (generate-temporaries '(t))))
(syntax (t ((t e))))))
(((unsyntax e ...) . r)
(= level 0)
(with-syntax (((r* (rep ...)) (expand (syntax r) 0))
((t ...) (generate-temporaries (syntax (e ...)))))
(syntax ((t ... . r*)
((t e) ... rep ...)))))
(((unsyntax-splicing e ...) . r)
(= level 0)
(with-syntax (((r* (rep ...)) (expand (syntax r) 0))
((t ...) (generate-temporaries (syntax (e ...)))))
(with-syntax ((((t ...) ...) (syntax ((t (... ...)) ...))))
(syntax ((t ... ... . r*)
(((t ...) e) ... rep ...))))))
((k . r)
(and (> level 0)
(identifier? (syntax k))
(or (free-identifier=? (syntax k) (syntax unsyntax))
(free-identifier=? (syntax k) (syntax unsyntax-splicing))))
(with-syntax (((r* reps) (expand (syntax r) (- level 1))))
(syntax ((k . r*) reps))))
((h . t)
(with-syntax (((h* (rep1 ...)) (expand (syntax h) level))
((t* (rep2 ...)) (expand (syntax t) level)))
(syntax ((h* . t*)
(rep1 ... rep2 ...)))))
(#(e ...)
(with-syntax ((((e* ...) reps)
(expand (vector->list (syntax #(e ...))) level)))
(syntax (#(e* ...) reps))))
(other
(syntax (other ())))))
(syntax-case e ()
((_ template)
(with-syntax (((template* replacements) (expand (syntax template) 0)))
(syntax
(with-syntax replacements (syntax template*))))))))
(define-syntax unsyntax
(lambda (e)
(syntax-violation 'unsyntax "Invalid expression" e)))
(define-syntax unsyntax-splicing
(lambda (e)
(syntax-violation 'unsyntax "Invalid expression" e)))
|