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Doc Bug #40996 Floating point grammar omits signed numbers
Submitted: 2007-04-04 14:56 UTC Modified: 2007-08-17 10:42 UTC
From: ehanneken at pobox dot com Assigned:
Status: Not a bug Package: Documentation problem
PHP Version: Irrelevant OS:
Private report: No CVE-ID: None
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From: ehanneken at pobox dot com
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 [2007-04-04 14:56 UTC] ehanneken at pobox dot com 
Description:
------------
According to the manual (http://www.php.net/manual/en/language.types.float.php), the following grammar specifies floating point numbers:

LNUM          [0-9]+
DNUM          ([0-9]*[\.]{LNUM}) | ({LNUM}[\.][0-9]*)
EXPONENT_DNUM ( ({LNUM} | {DNUM}) [eE][+-]? {LNUM})

This leaves out signed numbers.  The grammar should be written as something like

ULNUM          [0-9]+
SLNUM          [+-]{ULNUM}
DNUM           [+-]?(([0-9]*[\.]{ULNUM}) | ({ULNUM}[\.][0-9]*))
EXPONENT_DNUM  [+-]?( ({ULNUM} | {DNUM}) [eE][+-]? {ULNUM})


Reproduce code:
---------------
echo gettype(-3.14) . "\n";
echo gettype(+3.14);


Expected result:
----------------
double
double

Actual result:
--------------
double
double

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 [2007-04-04 15:03 UTC] ehanneken at pobox dot com 
There was a bug in my revised grammer, too.  How about this?

ULNUM          [0-9]+
SLNUM          [+-]{ULNUM}
DNUM           [+-]?(([0-9]*[\.]{ULNUM}) | ({ULNUM}[\.][0-9]*))
EXPONENT_DNUM  ( ({SLNUM} | {DNUM}) [eE][+-]? {ULNUM})
 [2007-04-04 15:03 UTC] ehanneken at pobox dot com 
There was a bug in my revised grammar, too.  How about this?

ULNUM          [0-9]+
SLNUM          [+-]{ULNUM}
DNUM           [+-]?(([0-9]*[\.]{ULNUM}) | ({ULNUM}[\.][0-9]*))
EXPONENT_DNUM  ( ({SLNUM} | {DNUM}) [eE][+-]? {ULNUM})
 [2007-04-08 19:40 UTC] ezyang@php.net 
I wonder whether or not we should have the formal grammar at all. We're not trying to teach people how to parse floating point numbers: just tell them how to write them out. Plus, it's not even stated what the grammar is written in! (it's certainly not EBNF, not a Perl regexp due to extra spacing, what is it?)

The formal grammar was added by jeroen in v1.21 as a comment, which goba turned into an actual section later on.

The PHP parser doesn't "natively" recognize signs to the float syntax: so +-+-+-+3.4, while very strange, does work with the PHP parser. Instead, we're really using + and - operator to change the sign of the float. I.e.

-4.2 == -(4.2) to the PHP parser

For the average Joe, I don't think this distinction makes much difference though.

Finally, the revised grammar has a bug: it doesn't include "unsigned" exponential non-decimal numbers, eg. 4e4.
 [2007-08-17 10:42 UTC] vrana@php.net 
Not a bug as explained by ezyang.
 
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