[luatex] luatex problem with file with umlauts on windows 10

[Reinhard Kotucha]

On 2020-04-26 at 17:12:08 +0200, Ulrike Fischer wrote:

 > Am Sun, 26 Apr 2020 11:00:50 +0100 schrieb Philip Taylor:
 > 
 > > Trying to understand why Akira-san had written :
 > > 
 > >>
 > >>         local function is_texlive ()
 > >>              local a = kpse.var_value ('command_line_encoding')
 > >>              if a
 > >>              then
 > >>                    return true
 > >>              else
 > >>                    return false
 > >>              end
 > >>         end
 > > 
 > > rather than
 > > 
 > >>         local function is_texlive ()
 > >>              local a = kpse.var_value ('command_line_encoding')
 > >>              return a
 > >>         end
 > > 
 > 
 > because a is = "utf-8" and  not "true" in texlive. 

But Lua treats everything as true in boolean expressions which is not
false or nil.  Thus one could even write

local function is_texlive ()
  return kpse.var_value ('command_line_encoding')
end

is_texlive () returns either a string (true) or nil (false).  I
suppose that kpathsea returns nil if the variable
command_line_encoding is not defined.

BTW, unless you have to distinguish between nil and false something
like

  else return false

is not necessary.  You could also write

  else return nil

which has the same effect as omitting the return statement completely.


 > Try 
 > 
 > \directlua{ local a = kpse.var_value ('command_line_encoding')
 > print(a)}

Better force a into a boolean context.  One possibility is double
negation:

$ lua
Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio
> print(type(a))
nil
> print (not not a)
false
> a = 'hello'
> print(type(a))
string
> print (not not a)
true
> os.exit()

Regards,
  Reinhard


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Reinhard Kotucha                            Phone: +49-511-3373112
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