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- Subject: How to extract a floating point number locale-independantly
- From: Daurnimator <quae@...>
- Date: Tue, 26 Apr 2016 11:55:01 +1000
I had a report that some of my code was failing in the nb_NO-utf8 locale:
Indeed, `tonumber` behaves differently depending on locale:
$ lua -e 'os.setlocale("nb_NO.utf-8") print(tonumber("1.0"))'
$ lua -e 'os.setlocale("nb_NO.utf-8") print(tonumber("1,0"))'
However it *doesn't* affect lua parsing; which seems to be against the manual.
> The conversion of strings can result in integers or floats, according to the lexical conventions
> of Lua (see §3.1). (The string may have leading and trailing spaces and a sign.)
$ lua -e 'os.setlocale("nb_NO.utf-8") print(load([[return 1.0]])())'
$ lua -e 'os.setlocale("nb_NO.utf-8") print(load([[return 1,0]])())'
This leaves me with the question of how to deserialise a floating
point number within a lua library (where I can't control the locale of
Normally I'd write something like:
local mystring = "some protocol 1.0"
local version = mystring:match("(%d+%.%d*)") --> version == "1.0"
version = tonumber(version) --> version == 1.0
Or using lpeg:
local digit = lpeg.R "09"
local version_patt = digit^1 * lpeg.P "." * digit^0 / tonumber
local parser = something * version_patt
local version = parser:match "some protocol 1.0" --> version == 1.0
But this doesn't work in some locales :(
What do other people do? and is there a good solution?