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Resolve all placeholders before patching. Allows direct links (#0=#=0). 

Definitions and references can be made in any order.
Cyclic placeholders resolve to #<undefined>, as do ones without definitions.
This commit is contained in:
Jesse D. McDonald 2009-11-14 17:06:58 -06:00
parent 48eb22d15b
commit 902c489b90
1 changed files with 25 additions and 15 deletions
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40
reader.c
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@ -30,7 +30,7 @@ static value_t read_struct(reader_state_t *state);
static value_t read_weak_box(reader_state_t *state);
static value_t read_definition(reader_state_t *state);
static value_t read_backref(reader_state_t *state);
static value_t read_placeholder(reader_state_t *state);
static void next_char(reader_state_t *state);
static void skip_whitespace(reader_state_t *state);
@ -38,7 +38,7 @@ static void skip_whitespace(reader_state_t *state);
static bool is_placeholder(reader_state_t *state, value_t value);
static value_t get_placeholder(reader_state_t *state, fixnum_t ref);
static void set_placeholder(reader_state_t *state, value_t place, value_t value);
static value_t finalize_placeholder(reader_state_t *state, value_t place);
static void finalize_placeholders(reader_state_t *state);
static value_t patch_placeholders(reader_state_t *state, value_t v);
static void tree_replace(value_t *in, value_t oldval, value_t newval);
@ -144,7 +144,7 @@ static value_t read_special(reader_state_t *state)
case '0' ... '9':
return read_definition(state);
case '=':
return read_backref(state);
return read_placeholder(state);
default:
release_assert(NOTREACHED("Invalid character in special value."));
return UNDEFINED;
@ -493,14 +493,13 @@ static value_t read_definition(reader_state_t *state)
register_gc_root(&place_root, get_placeholder(state, ref));
v = read_one_value(state);
release_assert(!is_placeholder(state, v));
set_placeholder(state, place_root.value, v);
unregister_gc_root(&place_root);
return v;
}
static value_t read_backref(reader_state_t *state)
static value_t read_placeholder(reader_state_t *state)
{
next_char(state);
skip_whitespace(state);
@ -552,25 +551,36 @@ static void set_placeholder(reader_state_t *state, value_t place, value_t value)
_CADR(place) = value;
}
static value_t finalize_placeholder(reader_state_t *state, value_t place)
static void finalize_placeholders(reader_state_t *state)
{
assert(is_placeholder(state, place));
if (is_placeholder(state, _CADR(place)))
for (bool changed = true; changed; changed = false)
{
value_t other_place = _CADR(place);
_CADR(place) = UNDEFINED;
_CADR(place) = finalize_placeholder(state, other_place);
/* On each cycle, placeholder cycles/lists should come one link closer to self or actual value.
* Self-links indicate cycles and are replaced with UNDEFINED.
* We're done when no placeholders link to other placeholders. */
for (value_t item = state->ref_alist.value; !is_nil(item); item = _CDDR(item))
{
if (_CADR(item) == item)
{
_CADR(item) = UNDEFINED;
changed = true;
}
else if (is_placeholder(state, _CADR(item)))
{
_CADR(item) = _CADR(_CADR(item));
changed = true;
}
}
}
return _CADR(place);
}
static value_t patch_placeholders(reader_state_t *state, value_t v)
{
finalize_placeholders(state);
for (value_t item = state->ref_alist.value; !is_nil(item); item = _CDDR(item))
{
tree_replace(&v, item, finalize_placeholder(state, item));
tree_replace(&v, item, _CADR(item));
}
return v;