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Diffstat (limited to 'libguile/eval.c')
-rw-r--r-- | libguile/eval.c | 179 |
1 files changed, 0 insertions, 179 deletions
diff --git a/libguile/eval.c b/libguile/eval.c index 8f2f5d02f..30da3424b 100644 --- a/libguile/eval.c +++ b/libguile/eval.c @@ -3422,185 +3422,6 @@ SCM_DEFINE (scm_promise_p, "promise?", 1, 0, 0, #undef FUNC_NAME -SCM_DEFINE (scm_cons_source, "cons-source", 3, 0, 0, - (SCM xorig, SCM x, SCM y), - "Create and return a new pair whose car and cdr are @var{x} and @var{y}.\n" - "Any source properties associated with @var{xorig} are also associated\n" - "with the new pair.") -#define FUNC_NAME s_scm_cons_source -{ - SCM p, z; - z = scm_cons (x, y); - /* Copy source properties possibly associated with xorig. */ - p = scm_whash_lookup (scm_source_whash, xorig); - if (scm_is_true (p)) - scm_whash_insert (scm_source_whash, z, p); - return z; -} -#undef FUNC_NAME - - -/* The function scm_copy_tree is used to copy an expression tree to allow the - * memoizer to modify the expression during memoization. scm_copy_tree - * creates deep copies of pairs and vectors, but not of any other data types, - * since only pairs and vectors will be parsed by the memoizer. - * - * To avoid infinite recursion due to cyclic structures, the hare-and-tortoise - * pattern is used to detect cycles. In fact, the pattern is used in two - * dimensions, vertical (indicated in the code by the variable names 'hare' - * and 'tortoise') and horizontal ('rabbit' and 'turtle'). In both - * dimensions, the hare/rabbit will take two steps when the tortoise/turtle - * takes one. - * - * The vertical dimension corresponds to recursive calls to function - * copy_tree: This happens when descending into vector elements, into cars of - * lists and into the cdr of an improper list. In this dimension, the - * tortoise follows the hare by using the processor stack: Every stack frame - * will hold an instance of struct t_trace. These instances are connected in - * a way that represents the trace of the hare, which thus can be followed by - * the tortoise. The tortoise will always point to struct t_trace instances - * relating to SCM objects that have already been copied. Thus, a cycle is - * detected if the tortoise and the hare point to the same object, - * - * The horizontal dimension is within one execution of copy_tree, when the - * function cdr's along the pairs of a list. This is the standard - * hare-and-tortoise implementation, found several times in guile. */ - -struct t_trace { - struct t_trace *trace; /* These pointers form a trace along the stack. */ - SCM obj; /* The object handled at the respective stack frame.*/ -}; - -static SCM -copy_tree ( - struct t_trace *const hare, - struct t_trace *tortoise, - unsigned int tortoise_delay ) -{ - if (!scm_is_pair (hare->obj) && !scm_is_simple_vector (hare->obj)) - { - return hare->obj; - } - else - { - /* Prepare the trace along the stack. */ - struct t_trace new_hare; - hare->trace = &new_hare; - - /* The tortoise will make its step after the delay has elapsed. Note - * that in contrast to the typical hare-and-tortoise pattern, the step - * of the tortoise happens before the hare takes its steps. This is, in - * principle, no problem, except for the start of the algorithm: Then, - * it has to be made sure that the hare actually gets its advantage of - * two steps. */ - if (tortoise_delay == 0) - { - tortoise_delay = 1; - tortoise = tortoise->trace; - ASSERT_SYNTAX (!scm_is_eq (hare->obj, tortoise->obj), - s_bad_expression, hare->obj); - } - else - { - --tortoise_delay; - } - - if (scm_is_simple_vector (hare->obj)) - { - size_t length = SCM_SIMPLE_VECTOR_LENGTH (hare->obj); - SCM new_vector = scm_c_make_vector (length, SCM_UNSPECIFIED); - - /* Each vector element is copied by recursing into copy_tree, having - * the tortoise follow the hare into the depths of the stack. */ - unsigned long int i; - for (i = 0; i < length; ++i) - { - SCM new_element; - new_hare.obj = SCM_SIMPLE_VECTOR_REF (hare->obj, i); - new_element = copy_tree (&new_hare, tortoise, tortoise_delay); - SCM_SIMPLE_VECTOR_SET (new_vector, i, new_element); - } - - return new_vector; - } - else /* scm_is_pair (hare->obj) */ - { - SCM result; - SCM tail; - - SCM rabbit = hare->obj; - SCM turtle = hare->obj; - - SCM copy; - - /* The first pair of the list is treated specially, in order to - * preserve a potential source code position. */ - result = tail = scm_cons_source (rabbit, SCM_EOL, SCM_EOL); - new_hare.obj = SCM_CAR (rabbit); - copy = copy_tree (&new_hare, tortoise, tortoise_delay); - SCM_SETCAR (tail, copy); - - /* The remaining pairs of the list are copied by, horizontally, - * having the turtle follow the rabbit, and, vertically, having the - * tortoise follow the hare into the depths of the stack. */ - rabbit = SCM_CDR (rabbit); - while (scm_is_pair (rabbit)) - { - new_hare.obj = SCM_CAR (rabbit); - copy = copy_tree (&new_hare, tortoise, tortoise_delay); - SCM_SETCDR (tail, scm_cons (copy, SCM_UNDEFINED)); - tail = SCM_CDR (tail); - - rabbit = SCM_CDR (rabbit); - if (scm_is_pair (rabbit)) - { - new_hare.obj = SCM_CAR (rabbit); - copy = copy_tree (&new_hare, tortoise, tortoise_delay); - SCM_SETCDR (tail, scm_cons (copy, SCM_UNDEFINED)); - tail = SCM_CDR (tail); - rabbit = SCM_CDR (rabbit); - - turtle = SCM_CDR (turtle); - ASSERT_SYNTAX (!scm_is_eq (rabbit, turtle), - s_bad_expression, rabbit); - } - } - - /* We have to recurse into copy_tree again for the last cdr, in - * order to handle the situation that it holds a vector. */ - new_hare.obj = rabbit; - copy = copy_tree (&new_hare, tortoise, tortoise_delay); - SCM_SETCDR (tail, copy); - - return result; - } - } -} - -SCM_DEFINE (scm_copy_tree, "copy-tree", 1, 0, 0, - (SCM obj), - "Recursively copy the data tree that is bound to @var{obj}, and return a\n" - "the new data structure. @code{copy-tree} recurses down the\n" - "contents of both pairs and vectors (since both cons cells and vector\n" - "cells may point to arbitrary objects), and stops recursing when it hits\n" - "any other object.") -#define FUNC_NAME s_scm_copy_tree -{ - /* Prepare the trace along the stack. */ - struct t_trace trace; - trace.obj = obj; - - /* In function copy_tree, if the tortoise makes its step, it will do this - * before the hare has the chance to move. Thus, we have to make sure that - * the very first step of the tortoise will not happen after the hare has - * really made two steps. This is achieved by passing '2' as the initial - * delay for the tortoise. NOTE: Since cycles are unlikely, giving the hare - * a bigger advantage may improve performance slightly. */ - return copy_tree (&trace, &trace, 2); -} -#undef FUNC_NAME - - /* We have three levels of EVAL here: - scm_i_eval (exp, env) |