diff options
| -rw-r--r-- | eval.c | 9 | ||||
| -rw-r--r-- | txr.1 | 51 |
2 files changed, 60 insertions, 0 deletions
@@ -2912,6 +2912,14 @@ static val me_qquote(val form, val menv) return expand_qquote(second(form), qquote_s, unquote_s, splice_s); } +static val me_equot(val form, val menv) +{ + if (!cdr(form) || cddr(form)) + eval_error(form, lit("~s: one argument required"), car(form)); + + return rlcp(cons(quote_s, cons(expand(cadr(form), menv), nil)), form); +} + static val expand_vars(val vars, val menv, val form, val *spec_p, int seq_p) { @@ -5068,6 +5076,7 @@ void eval_init(void) reg_mac(aret_s, func_n2(me_ret_aret)); reg_mac(qquote_s, func_n2(me_qquote)); reg_mac(sys_qquote_s, func_n2(me_qquote)); + reg_mac(intern(lit("equot"), user_package), func_n2(me_equot)); reg_mac(intern(lit("pprof"), user_package), func_n2(me_pprof)); reg_mac(when_s, func_n2(me_when)); reg_mac(intern(lit("unless"), user_package), func_n2(me_unless)); @@ -27990,6 +27990,57 @@ emanating from the .code delta form. +.coNP Macro @ equot +.synb +.mets (equot << form ) +.syne +.desc +The +.code equot +macro ("expand and quote") performs a full expansion of +.code form +in the surrounding macro environment. Then it constructs a +.code quote +form whose argument is the expansion. This quote form is +then returned as the macro replacement for the original +.code equot +form. + +.TP* Example: + +.cblk + (symacrolet ((a (+ 2 2))) + (list (quote a) (equot a) a)) + --> (a (+ 2 2) 4) +.cble + +Above, the expansion of +.code a +is +.codn "(+ 2 2)" . +Thus the macro call +.code "(equot a)" +expands to +.codn "(quote (+ 2 2))" . +When that is evaluated, it yields +.codn "(+ 2 2)" . + +If +.code a +is quoted, then of course the result is +.codn a : +no expansion or evaluation takes place. +Whereas if +.code a +is presented for evaluation, then not only is it expanded to +.codn "(+ 2 2)" , +but that expansion is reduced to 4. + +The +.code equot +operator is a mongrel of these two semantics: it permits expansion to proceed, +but then suppresses evaluation of the result. + .coNP Operators @ tree-bind and @ mac-param-bind .synb .mets (tree-bind < macro-style-params < expr << form *) |