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Fix behavior of fe_write() on circular lists #22

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Fix behavior of fe_write() on circular lists #22

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4 changes: 4 additions & 0 deletions scripts/circular.fe
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
(= items (list 1 2 3 4))
(setcar (cdr items) (cons items (cons 5 items)))
(setcdr (cdr (cdr (cdr items))) items)
(print items)
28 changes: 23 additions & 5 deletions src/fe.c
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Original file line number Diff line number Diff line change
Expand Up @@ -343,7 +343,7 @@ static void writestr(fe_Context *ctx, fe_WriteFn fn, void *udata, const char *s)
while (*s) { fn(ctx, udata, *s++); }
}

void fe_write(fe_Context *ctx, fe_Object *obj, fe_WriteFn fn, void *udata, int qt) {
static void write_(fe_Context *ctx, fe_Object *obj, fe_WriteFn fn, void *udata, int qt) {
char buf[32];

switch (type(obj)) {
Expand All @@ -357,22 +357,28 @@ void fe_write(fe_Context *ctx, fe_Object *obj, fe_WriteFn fn, void *udata, int q
break;

case FE_TPAIR:
if (tag(obj) & GCMARKBIT) { writestr(ctx, fn, udata, "..."); break; }
fn(ctx, udata, '(');
for (;;) {
fe_write(ctx, car(obj), fn, udata, 1);
/* mark 'obj' and write car(obj) */
fe_Object *tmp = car(obj);
tag(obj) |= GCMARKBIT;
write_(ctx, tmp, fn, udata, 1);
/* write cdr(obj) if isn't circular list */
obj = cdr(obj);
if (type(obj) != FE_TPAIR) { break; }
fn(ctx, udata, ' ');
if (tag(obj) & GCMARKBIT) { writestr(ctx, fn, udata, "..."); break; }
}
if (!isnil(obj)) {
if (!isnil(obj) && !(tag(obj) & GCMARKBIT)) {
writestr(ctx, fn, udata, " . ");
fe_write(ctx, obj, fn, udata, 1);
write_(ctx, obj, fn, udata, 1);
}
fn(ctx, udata, ')');
break;

case FE_TSYMBOL:
fe_write(ctx, car(cdr(obj)), fn, udata, 0);
write_(ctx, car(cdr(obj)), fn, udata, 0);
break;

case FE_TSTRING:
Expand All @@ -395,6 +401,18 @@ void fe_write(fe_Context *ctx, fe_Object *obj, fe_WriteFn fn, void *udata, int q
}
}

static void unmarkpairs(fe_Object *obj) {
for (; !isnil(obj) && (tag(obj) & GCMARKBIT); obj = cdr(obj)) {
tag(obj) &= ~GCMARKBIT;
unmarkpairs(car(obj));
}
}

void fe_write(fe_Context *ctx, fe_Object *obj, fe_WriteFn fn, void *udata, int qt) {
write_(ctx, obj, fn, udata, qt);
unmarkpairs(obj);
}


static void writefp(fe_Context *ctx, void *udata, char chr) {
unused(ctx);
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