On Tue, Nov 19, 2002 at 10:59:02AM -0800, Michael Lazzaro wrote:
: OK, back to this, so we can finish it up: we have a number of proposals
: & questions re: string-to-num conversions, and from Luke we have some
: initial docs for them that need completing. Can I get more feedback on
: these issues, plz, and any other String -> Number proposals/questions?
:
:
: (A) Unification of Literal <--> Stringified Numeric Behaviors
:
: An old proposal that I can't find anymore suggested that strings should
: be converted to a number according to the exact same rules as literals,
: such that:
:
: 0123 == "0123"
: 0xff == "0xff"
: 20#1gj == "20#1gj"
: 1e10 == "1e10"
:
: .... in the interest of regularity, flexibility, etc. Comments?
This is impossible unless we do away with 0123. There are too many
leading 0's in the decimal world. On the other hand, 0x is unlikely
to occur by accident.
: (B) We want to be able to convert strings to numbers, using strings in
: any of the formats that literals understand. If (A) is accepted, this
: is unnecessary: if not, we need a conversion syntax, maybe something
: like one of:
:
: my $s = "20#1gj";
:
: my num $i = literal $s; # (1a) literal is a func or unary op
: my num $i = numeric $s; # (1b) alternate spelling?
: my num $i = $s.literal; # (2a) str has method 'literal'
: my num $i = $s.numeric; # (2b)
A type constructor, so int() or num() (or Int() or Num()).
: (C) We sometimes want to be able to specify the _exact_ format a string
: should be expected as. Suppose you wanted a user to always enter a hex
: value: they should be able to just enter "10" or "ff", and you wanted
: to convert that to 16 and 255, respectively. So you'd maybe use
: something like:
:
: my $s = "ff"; # note there's no '0x' in front
:
: my int $i = hex $s;
: my int $i = $s.hex;
: my int $i = $s.numeric('%2x'); # ???
I will resist any attempt to introduce scanf() into the language.
: e.g. is "numeric" a method of str, and if so, can it accept formatting
: information? And are there shortcuts for the common cases that
: literals already know about, e.g. <<sci dec bin oct hex>>?
Note that oct and hex are backwards in that they don't produce octal or hex.
: (D) There were proposals to allow a given string to _always_ be
: numified in a certain way by attaching a property, e.g.:
:
: my str $s is formatted('%2x');
: $s = 'ff';
: my int $i = $s; # 255
:
: ....now I'm wondering if that's buying us anything, though the inverse
: seems much more useful:
:
: my int $i is formatted('%4x');
: $i = 255;
: print $i; # prints '00ff';
:
: Anyone care to comment? Compiletime property, runtime property, or
: both?
Seems like a type issue to me, not a property issue.
: (E) We need to finalize what happens when a string isn't a number, or
: has additional trailing stuff. Damian gave his initial preference, but
: we need to verify & set in stone:
:
: my int $i = 'foo'; # 0, NaN, undef, or exception?
: my int $i = '5foo'; # 5, NaN, undef, or exception?
:
: my Int $i = 'foo'; # 'Int' probably makes a difference
: my Int $i = '5foo';
Probably depends on the strictness level. But it should be easy to
get warnings at least, or to have values like "5 but bogus". :-)
I think we can afford to get a bit picker than Perl 5 on conversions, but
I'd still like it if "5\n" doesn't complain as much as "5foo".
Larry
