Parse from String and convert to float, integer (Raku)

Question

FAQ: In Raku, how do I parse a String and get a Number ? For example:

xxx("42");  # 42 (Int)
xxx("0x42");  # 66 (Int)
xxx("42.123456789123456789");  # 42.123456789123456789 (Rat)
xxx("42.4e2");  # 4240 (Rat)
xxx("42.4e-2");  # 0.424 (Rat)

Tinmarino · Accepted Answer · 2020-03-27T23:21:03.333

6

Just use the prefix +:

say +"42";  # 42 (Int)
say +"0x42";  # 66 (Int)
say +"42.123456789123456789";  # 42.123456789123456789 (Rat)
say +"42.4e2";  # 4240 (Rat)
say +"42.4e-2";  # 0.424 (Rat)

Info

val a Str routine is doing exactely what you (I) want.

Beware that it is returning Allomorph object. Use unival or just + prefix to convert it to Number

Links:
Learning Raku: Number, Strings, and NumberString Allomorphs
Same question in Python, Perl
Roseta Code: Determine if a string is numeric

Edited thanks to @Holli comment

edited Mar 27 '20 at 23:21

answered Mar 25 '20 at 16:56

Tinmarino

3,693
24
33

2

Normally you don't need `val`. You can just rely on automatic type conversion or just use the `+`. `say (+'0x42').WHAT; #Int`. – Holli Mar 25 '20 at 20:29

librasteve · Answer 2 · 2020-03-25T21:19:29.647

5

my regex number {
    \S+                     #grab chars 
    <?{ defined +"$/" }>    #assertion that coerces via '+' to Real
}

#strip factor [leading] e.g. 9/5 * Kelvin
if ( $defn-str ~~ s/( <number>? ) \s* \*? \s* ( .* )/$1/ ) {
    my $factor = $0;
    #...
}

edited Mar 25 '20 at 21:19

answered Mar 25 '20 at 21:09

librasteve

6,832
8
30

2

I use this combination of ‘+’ and look ahead assertion to test a sub string for Real. – librasteve Mar 25 '20 at 21:12
1

Nice watchguard to check : the `val` answer do not check and must be CATCH. – Tinmarino Mar 25 '20 at 21:28
Referenced, thank you! https://unix.stackexchange.com/a/708355/227738 – jubilatious1 Jul 02 '22 at 11:11

Parse from String and convert to float, integer (Raku)

2 Answers2