diff options
| -rw-r--r-- | eval.c | 5 | ||||
| -rw-r--r-- | lib.c | 17 | ||||
| -rw-r--r-- | lib.h | 3 | ||||
| -rw-r--r-- | txr.1 | 62 |
4 files changed, 81 insertions, 6 deletions
@@ -6343,8 +6343,11 @@ void eval_init(void) reg_mac(intern(lit("load-for"), user_package), func_n2(me_load_for)); reg_fun(cons_s, func_n2(cons)); - reg_fun(intern(lit("make-lazy-cons"), user_package), func_n1(make_lazy_cons)); + reg_fun(intern(lit("make-lazy-cons"), user_package), + func_n3o(make_lazy_cons_pub, 1)); reg_fun(intern(lit("lcons-fun"), user_package), func_n1(lcons_fun)); + reg_fun(intern(lit("lcons-car"), user_package), func_n1(lcons_car)); + reg_fun(intern(lit("lcons-cdr"), user_package), func_n1(lcons_cdr)); reg_fun(car_s, car_f); reg_fun(cdr_s, cdr_f); reg_fun(rplaca_s, func_n2(rplaca)); @@ -3022,6 +3022,23 @@ val make_lazy_cons_car_cdr(val func, val car, val cdr) return obj; } +val make_lazy_cons_pub(val func, val car, val cdr) +{ + return make_lazy_cons_car_cdr(func, default_null_arg(car), default_null_arg(cdr)); +} + +val lcons_car(val lcons) +{ + type_check(lit("lcons-car"), lcons, LCONS); + return lcons->lc.car; +} + +val lcons_cdr(val lcons) +{ + type_check(lit("lcons-cdr"), lcons, LCONS); + return lcons->lc.cdr; +} + void rcyc_cons(val cons) { cons->c.cdr = recycled_conses; @@ -665,6 +665,9 @@ val cons(val car, val cdr); val make_lazy_cons(val func); val make_lazy_cons_car(val func, val car); val make_lazy_cons_car_cdr(val func, val car, val cdr); +val make_lazy_cons_pub(val func, val car, val cdr); +val lcons_car(val lcons); +val lcons_cdr(val lcons); void rcyc_cons(val cons); void rcyc_list(val list); void rcyc_empty(void); @@ -20137,7 +20137,7 @@ functions than less functions, the excess key functions are ignored. .SS* Lazy Lists and Lazy Evaluation .coNP Function @ make-lazy-cons .synb -.mets (make-lazy-cons << function ) +.mets (make-lazy-cons < function >> [ car <> [ cdr ]]) .syne .desc The function @@ -20155,9 +20155,15 @@ A lazy cons has and .code cdr fields like a regular cons, and those -fields are initialized to -.code nil -when the lazy cons is created. A lazy cons also +fields are initialized to the values of the +.meta car +and +.meta cdr +arguments of +.code make-lazy-cons +when the lazy cons is created. These arguments default to +.meta nil +if omitted. A lazy cons also has an update function, which is specified by the .meta function argument to @@ -20182,13 +20188,20 @@ and .code cdr fields. Once the function is called, it is removed from the lazy cons: the lazy cons no longer has an update function. -If the function attempts to retrieve the value of the +If the update function itself attempts to retrieve the value of the lazy cons cell's .code car or .code cdr field, it will be recursively invoked. +The functions +.code lcons-car +and +.code lcons-cdr +may be used to access the fields of a lazy cons without +triggering the update function. + Storing a value into either the .code car or @@ -20271,6 +20284,45 @@ to retrieve a reference to itself and propagate itself into another lazy cons (as in the example under .codn make-lazy-cons ). +.coNP Functions @ lcons-car and @ lcons-cdr +.synb +.mets (lcons-car << lazy-cons ) +.mets (lcons-cdr << lazy-cons ) +.syne +.desc +The functions +.code lcons-car +and +.code lcons-cdr +retrieve the +.code car +and +.code cdr +fields of +.metn lazy-cons , +without triggering the invocation of its associated update function. + +The +.meta lazy-cons +argument must be an object of type +.codn lcons . +Unlike the functions +.code car +and +.codn cdr , +These functions cannot be applied to any other type of object. + +Note: these functions may be used by the update function to retrieve +the values which were stored into +.meta lazy-cons +by the +.code make-lazy-cons +constructor, without triggering recursion. The function may then +overwrite either or both of these values. This allows the fields of the lazy +cons to store state information necessary for the propagation of a lazy list. +If that state information consists of no more than two values, then +no additional context object need be allocated. + .coNP Macro @ lcons .synb .mets (lcons < car-expression << cdr-expression ) |