digitalmars.D.bugs - [Issue 3835] New: [CTFE] Fragile CTFE
- d-bugmail puremagic.com (37/37) Feb 18 2010 http://d.puremagic.com/issues/show_bug.cgi?id=3835
- d-bugmail puremagic.com (11/15) Feb 18 2010 http://d.puremagic.com/issues/show_bug.cgi?id=3835
- d-bugmail puremagic.com (57/58) Feb 19 2010 OK. This two versions of genFactorials print the wrong results:
- d-bugmail puremagic.com (42/42) Mar 01 2010 http://d.puremagic.com/issues/show_bug.cgi?id=3835
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- d-bugmail puremagic.com (13/13) Apr 08 2011 http://d.puremagic.com/issues/show_bug.cgi?id=3835
http://d.puremagic.com/issues/show_bug.cgi?id=3835
Summary: [CTFE] Fragile CTFE
Product: D
Version: 2.040
Platform: Other
OS/Version: Windows
Status: NEW
Severity: normal
Priority: P2
Component: DMD
AssignedTo: nobody puremagic.com
ReportedBy: bearophile_hugs eml.cc
This code (that uses CTFE to do something that can be useful, it initializes an
array with values compiled at compile time) compiles and works correctly, but I
think it's too much fragile: if you change the for loop a little, or other
details in genFactorials(), the program stops compiling:
int factorial(int n) {
if (n == 0)
return 1;
return n * factorial(n - 1);
}
int[] genFactorials(int n) {
int[] result;
for (; n >= 0; --n)
result = factorial(n) ~ result;
return result;
}
const int N = 13;
static const auto factorials = cast(int[N])genFactorials(N - 1);
void main() {}
If you need them, I can show many variants of this program that don't
compile/work.
I think to be useful in real programs CTFE has to be less fragile than this.
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Feb 18 2010
d-bugmail puremagic.com
http://d.puremagic.com/issues/show_bug.cgi?id=3835
Don <clugdbug yahoo.com.au> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |clugdbug yahoo.com.au
This code (that uses CTFE to do something that can be useful, it initializes an
array with values compiled at compile time) compiles and works correctly, but I
think it's too much fragile: if you change the for loop a little, or other
details in genFactorials(), the program stops compiling:
Please put in an example that it wouldn't compile!
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Feb 18 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3835Please put in an example that it wouldn't compile!OK. This two versions of genFactorials print the wrong results: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 import std.stdio: writeln; int factorial(int n) { if (n == 0) return 1; return n * factorial(n - 1); } int[] genFactorialsA(int n) { int[] result = new int[n + 1]; foreach (i, ref el; result) el = factorial(i); return result; } int[N] genFactorialsB(int N)() { int[N] result; foreach (i, ref el; result) el = factorial(i); return result; } enum int N = 13; static enum auto factorials1 = cast(int[N])genFactorialsA(N - 1); enum auto factorials2 = genFactorialsB!13; void main() { writeln(factorials1); writeln(factorials2); } This version doesn't compile, the compiler raises: test7b.d(7): Error: pure function 'factorial' cannot call impure function 'factorial' test7b.d(12): Error: pure function 'genFactorials' cannot call impure function 'factorial' test7b.d(17): Error: cannot evaluate genFactorials(12) at compile time test7b.d(17): Error: cannot evaluate genFactorials(12) at compile time import std.stdio: writeln; pure int[] genFactorials(int n) { pure static int factorial(int n) { if (n == 0) return 1; return n * factorial(n - 1); } int[] result = new int[n + 1]; foreach (i; 0 .. n+1) result[i] = factorial(i); return result; } enum int N = 13; static enum auto factorials = cast(int[N])genFactorials(N - 1); void main() { writeln(factorials); } -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 19 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3835
Serg Kovrov <kovrov+puremagic gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |kovrov+puremagic gmail.com
15:09:52 PST ---
Looks like foreach do not work in CTFE. Here is example with two equivalent
functions, one uses 'for', other 'foreach' loops:
uint[256] crc32_table_for()
{
uint[256] table;
for (uint i = 0; i < 256; ++i) {
uint crc = i;
for (int j = 0; j < 8; j++)
crc = crc & 1 ? (crc >> 1) ^ 0xEDB88320 : crc >> 1;
table[i] = crc;
}
return table;
}
uint[256] crc32_table_foreach()
{
uint[256] table;
foreach (n, ref i; table) {
uint crc = n;
foreach (j; 0 .. 8)
crc = crc & 1 ? (crc >> 1) ^ 0xEDB88320 : crc >> 1;
i = crc;
}
return table;
}
immutable crc32_table1 = crc32_table_for();
immutable crc32_table2 = crc32_table_foreach();
import std.stdio;
void main()
{
writefln("%s", crc32_table1);
writefln("%s", crc32_table2);
assert (crc32_table1 == crc32_table2);
}
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Mar 01 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3835 I think foreach(x; items) works in CTFE, but foreach(ref x; items) doesn't work well. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 01 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3835 The first two cases are already present in bug 2411. I don't know about the third. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 07 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3835 I created bug 3912 for the third bug mentioned in the comments, which has nothing to do with CTFE. Maybe this bug can now be marked as a duplicate of bug 2411? -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 09 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3835 You can mark this as duplicate. But when an improvement is created, it's necessary to try it with *all* duplicated examples too, because you must be sure they are really problems with the same cause. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 09 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3835
Don <clugdbug yahoo.com.au> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |rejects-valid
Summary|[CTFE] Fragile CTFE |ref foreach does not work
| |in CTFE
Bug 2411 is NOT the same as this. (2411 does not involve CTFE). Changing title.
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Mar 10 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3835
In dmd 2.043 my second tests cases works:
import std.stdio: writeln;
pure int[] genFactorials(int n) {
pure static int factorial(int n) {
if (n == 0)
return 1;
return n * factorial(n - 1);
}
int[] result = new int[n + 1];
foreach (i; 0 .. n+1)
result[i] = factorial(i);
return result;
}
enum int N = 13;
static enum auto factorials = cast(int[N])genFactorials(N - 1);
void main() {
writeln(factorials);
}
The first test case doesn't work yet.
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Apr 10 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3835
A reduced test case:
int foo() {
int[1] arr;
foreach (ref el; arr)
el = 10;
return arr[0];
}
enum int r = foo();
void main() {
assert(r == 10);
}
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Apr 10 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3835
klickverbot <code klickverbot.at> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |code klickverbot.at
---
This bug is worse than it might seem from reading the »rejects-valid« keyword
–
DMD 2.051 happily executes ref foreach during compile-time, but generates wrong
results silently.
Should we add a »wrong-ctfe« tag or something like that?
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Feb 06 2011
http://d.puremagic.com/issues/show_bug.cgi?id=3835
Don <clugdbug yahoo.com.au> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
This bug is worse than it might seem from reading the »rejects-valid«
keyword –
DMD 2.051 happily executes ref foreach during compile-time, but generates wrong
results silently.
Should we add a »wrong-ctfe« tag or something like that?
No, incorrect CTFE should just be marked as wrong-code. Yup, this one's
important.
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Feb 07 2011
http://d.puremagic.com/issues/show_bug.cgi?id=3835
Don <clugdbug yahoo.com.au> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
Fixed.
D2:
https://github.com/D-Programming-Language/dmd/commit/0219a5f0dcc88076759a4c472582954d0fb804b0
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Apr 08 2011