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digitalmars.D.learn - Hex floats

reply "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
What's the original rationale for requiring that hex float literals must
always have an exponent? For example, 0xFFi obviously must be float, not
integer, so why does the compiler (and the spec) require an exponent?

Also, the specs say:

	FloatLiteral:
		Float
		Float Suffix
		...

	Float:
		DecimalFloat
		HexFloat

	Suffix:
		FloatSuffix
		...

	FloatSuffix:
		f
		F

This is ambiguous, since you could interpret 0xFFp0F as either 0xFFp0
followed by the suffix 'F', or 0xFFp0F with an exponent of 0x0F no
suffix.


T

-- 
It is widely believed that reinventing the wheel is a waste of time; but
I disagree: without wheel reinventers, we would be still be stuck with
wooden horse-cart wheels.
Feb 15 2012
next sibling parent reply Don Clugston <dac nospam.com> writes:
On 15/02/12 22:24, H. S. Teoh wrote:

 What's the original rationale for requiring that hex float literals must
 always have an exponent? For example, 0xFFi obviously must be float, not
 integer, so why does the compiler (and the spec) require an exponent?



The syntax comes from C99.
Feb 16 2012
parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
On 16/02/2012 12:04, Don Clugston wrote:

 On 15/02/12 22:24, H. S. Teoh wrote:

 What's the original rationale for requiring that hex float literals must
 always have an exponent? For example, 0xFFi obviously must be float, not
 integer, so why does the compiler (and the spec) require an exponent?



 The syntax comes from C99.



Do you mean the syntax has just been copied straight from C99 without any
thought about 
making it more lenient?

Stewart.
Feb 16 2012
parent reply Don Clugston <dac nospam.com> writes:
On 16/02/12 13:28, Stewart Gordon wrote:

 On 16/02/2012 12:04, Don Clugston wrote:

 On 15/02/12 22:24, H. S. Teoh wrote:

 What's the original rationale for requiring that hex float literals must
 always have an exponent? For example, 0xFFi obviously must be float, not
 integer, so why does the compiler (and the spec) require an exponent?



 The syntax comes from C99.



 Do you mean the syntax has just been copied straight from C99 without
 any thought about making it more lenient?

 Stewart.



Yes. There would need to be a good reason to do so.

For the case in question, note that mathematically, imaginary integers 
are perfectly valid. Would an imaginary integer literal be an idouble, a 
ifloat, or an ireal? I don't think it could be any:

foor(float x)
foor(double x)
fooi(ifloat x)
fooi(idouble x)

foor(7); //ambiguous, doesn't compile
fooi(7i); // by symmetry, this shouldn't compile either
Feb 16 2012
parent reply Timon Gehr <timon.gehr gmx.ch> writes:
On 02/16/2012 05:06 PM, Don Clugston wrote:

 On 16/02/12 13:28, Stewart Gordon wrote:

 On 16/02/2012 12:04, Don Clugston wrote:

 On 15/02/12 22:24, H. S. Teoh wrote:

 What's the original rationale for requiring that hex float literals
 must
 always have an exponent? For example, 0xFFi obviously must be float,
 not
 integer, so why does the compiler (and the spec) require an exponent?



 The syntax comes from C99.



 Do you mean the syntax has just been copied straight from C99 without
 any thought about making it more lenient?

 Stewart.



 Yes. There would need to be a good reason to do so.

 For the case in question, note that mathematically, imaginary integers
 are perfectly valid. Would an imaginary integer literal be an idouble, a
 ifloat, or an ireal? I don't think it could be any:

 foor(float x)
 foor(double x)
 fooi(ifloat x)
 fooi(idouble x)

 foor(7); //ambiguous, doesn't compile
 fooi(7i); // by symmetry, this shouldn't compile either



static assert(is(typeof(7i)==idouble));
Feb 16 2012
parent reply Don Clugston <dac nospam.com> writes:
On 16/02/12 17:36, Timon Gehr wrote:

 On 02/16/2012 05:06 PM, Don Clugston wrote:

 On 16/02/12 13:28, Stewart Gordon wrote:

 On 16/02/2012 12:04, Don Clugston wrote:

 On 15/02/12 22:24, H. S. Teoh wrote:

 What's the original rationale for requiring that hex float literals
 must
 always have an exponent? For example, 0xFFi obviously must be float,
 not
 integer, so why does the compiler (and the spec) require an exponent?



 The syntax comes from C99.



 Do you mean the syntax has just been copied straight from C99 without
 any thought about making it more lenient?

 Stewart.



 Yes. There would need to be a good reason to do so.

 For the case in question, note that mathematically, imaginary integers
 are perfectly valid. Would an imaginary integer literal be an idouble, a
 ifloat, or an ireal? I don't think it could be any:

 foor(float x)
 foor(double x)
 fooi(ifloat x)
 fooi(idouble x)

 foor(7); //ambiguous, doesn't compile
 fooi(7i); // by symmetry, this shouldn't compile either



 static assert(is(typeof(7i)==idouble));



Ooh, that's bad.
Feb 17 2012
parent Timon Gehr <timon.gehr gmx.ch> writes:
On 02/17/2012 10:45 AM, Don Clugston wrote:

 On 16/02/12 17:36, Timon Gehr wrote:

 On 02/16/2012 05:06 PM, Don Clugston wrote:

 On 16/02/12 13:28, Stewart Gordon wrote:

 On 16/02/2012 12:04, Don Clugston wrote:

 On 15/02/12 22:24, H. S. Teoh wrote:

 What's the original rationale for requiring that hex float literals
 must
 always have an exponent? For example, 0xFFi obviously must be float,
 not
 integer, so why does the compiler (and the spec) require an exponent?



 The syntax comes from C99.



 Do you mean the syntax has just been copied straight from C99 without
 any thought about making it more lenient?

 Stewart.



 Yes. There would need to be a good reason to do so.

 For the case in question, note that mathematically, imaginary integers
 are perfectly valid. Would an imaginary integer literal be an idouble, a
 ifloat, or an ireal? I don't think it could be any:

 foor(float x)
 foor(double x)
 fooi(ifloat x)
 fooi(idouble x)

 foor(7); //ambiguous, doesn't compile
 fooi(7i); // by symmetry, this shouldn't compile either



 static assert(is(typeof(7i)==idouble));



 Ooh, that's bad.



Indeed. But the implementation of complex and imaginary numbers is 
pretty much broken in the front-end anyway. For example, double and 
idouble are type combined to double iirc.
Feb 17 2012
prev sibling parent "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Fri, Feb 17, 2012 at 02:41:10PM +0100, Timon Gehr wrote:

 On 02/17/2012 10:45 AM, Don Clugston wrote:

On 16/02/12 17:36, Timon Gehr wrote:







static assert(is(typeof(7i)==idouble));



Ooh, that's bad.



 Indeed. But the implementation of complex and imaginary numbers is
 pretty much broken in the front-end anyway. For example, double and
 idouble are type combined to double iirc.



Hmph. So complex literals are deprecated, right? So I should disable
them in my lexer? I assume Phobos doesn't use them anymore?


T

-- 
Without geometry, life would be pointless. -- VS
Feb 17 2012