integer displayed as .0 float in Lua-5.3

integer displayed as .0 float in Lua-5.3

[Pablo Rodriguez]

Dear list,

I have the following sample

    \starttext
    \startTEXpage[offset=1em]
    Pages: \ctxlua{context([[\lastpage]])}.

    Next page: \ctxlua{context([[\lastpage]] + 1)}.

    (Lua \luaversion)
    \stopTEXpage
    \stoptext

With Lua-5.2 (ConTeXt with JIT), I get the expected results. But with
Lua-5.3 (standard ConTeXt), I get 2.0 as the value for the next page.

I’m afraid that there is a bug here. I was told that the integer type
has been introduced in Lua-5.3.

I had experienced the same issue with the handlecsv module. In my very
limited understanding of the issue, integers are displayed as .0 floats.
I wonder which would be the way to fix it.

Is this a real bug or am I missing something?

Many thanks for your help,

Pablo
-- 
http://www.ousia.tk
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Re: integer displayed as .0 float in Lua-5.3

[Wolfgang Schuster]

Use tonumber.

%%%%%%
\starttext

\cldcontext{\lastpage + 1}

\cldcontext{"\lastpage" + 1}

\cldcontext{tonumber("\lastpage") + 1}

\stoptext
%%%%%%

Wolfgang


Pablo Rodriguez schrieb am 09.08.18 um 20:02:
> Dear list,
>
> I have the following sample
>
>      \starttext
>      \startTEXpage[offset=1em]
>      Pages: \ctxlua{context([[\lastpage]])}.
>
>      Next page: \ctxlua{context([[\lastpage]] + 1)}.
>
>      (Lua \luaversion)
>      \stopTEXpage
>      \stoptext
>
> With Lua-5.2 (ConTeXt with JIT), I get the expected results. But with
> Lua-5.3 (standard ConTeXt), I get 2.0 as the value for the next page.
>
> I’m afraid that there is a bug here. I was told that the integer type
> has been introduced in Lua-5.3.
>
> I had experienced the same issue with the handlecsv module. In my very
> limited understanding of the issue, integers are displayed as .0 floats.
> I wonder which would be the way to fix it.
>
> Is this a real bug or am I missing something?
>
> Many thanks for your help,
>
> Pablo

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Re: integer displayed as .0 float in Lua-5.3

[Pablo Rodriguez]

On 08/09/2018 08:12 PM, Wolfgang Schuster wrote:
> Use tonumber.

Many thanks for your reply, Wolfgang.

The issue is in Lua itself:

  print(5+"5")

In versions prior to 5.3, result is "10".

From version 5.3, result is "10.0",

I would say this might be a bug. According to the “Lua 5.3 Reference
Manual" (https://www.lua.org/manual/5.3/manual.html#3.1):

  A numeric constant with a radix point or an exponent denotes a
  float; otherwise, if its value fits in an integer, it denotes an
  integer.

Well, "10.0" contains the radix point, but with no arithmetical relevance.

My background is in humanities and I don’t understand the exponent for
being a float ("10²" contains an exponent
[https://www.m-w.com/dictionary/exponent], but I would say is an integer
in all possible worlds [or all the worlds I know ]).

Could anyone explain me what am I missing here or confirm whether this
is a bug?

Many thanks for your help,

Pablo
-- 
http://www.ousia.tk
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Re: integer displayed as .0 float in Lua-5.3

[Alan Braslau]

The lua manual also states that one should NOT rely on the implicit conversion of a string to its numerical value, and suggests the systematic use of tonumber().

Alan


On Thu, 9 Aug 2018 21:20:54 +0200
Pablo Rodriguez <oinos@gmx.es> wrote:

> On 08/09/2018 08:12 PM, Wolfgang Schuster wrote:
> > Use tonumber.  
> 
> Many thanks for your reply, Wolfgang.
> 
> The issue is in Lua itself:
> 
>   print(5+"5")
> 
> In versions prior to 5.3, result is "10".
> 
> From version 5.3, result is "10.0",
> 
> I would say this might be a bug. According to the “Lua 5.3 Reference
> Manual" (https://www.lua.org/manual/5.3/manual.html#3.1):
> 
>   A numeric constant with a radix point or an exponent denotes a
>   float; otherwise, if its value fits in an integer, it denotes an
>   integer.
> 
> Well, "10.0" contains the radix point, but with no arithmetical relevance.
> 
> My background is in humanities and I don’t understand the exponent for
> being a float ("10²" contains an exponent
> [https://www.m-w.com/dictionary/exponent], but I would say is an integer
> in all possible worlds [or all the worlds I know ]).
> 
> Could anyone explain me what am I missing here or confirm whether this
> is a bug?
> 
> Many thanks for your help,
> 
> Pablo

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Re: integer displayed as .0 float in Lua-5.3

[Pablo Rodriguez]

On 08/09/2018 09:34 PM, Alan Braslau wrote:
> The lua manual also states that one should NOT rely on the implicit
> conversion of a string to its numerical value, and suggests the
> systematic use of tonumber().

Many thanks for your reply, Alan.

I guess that backwards compatibility should be important here, but I
hope there are stronger reasons for breaking it.

Many thanks for your help,

Pablo
-- 
http://www.ousia.tk
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Re: integer displayed as .0 float in Lua-5.3

[Alan Braslau]

On Thu, 9 Aug 2018 22:00:48 +0200
Pablo Rodriguez <oinos@gmx.es> wrote:

> I guess that backwards compatibility should be important here, but I
> hope there are stronger reasons for breaking it.

tonumber() provides backwards compatibility. And the recommendation to use it was in the third edition (of the lua book), if not before, referring to 5.2.

Alan
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Re: integer displayed as .0 float in Lua-5.3

[Pablo Rodriguez]

On 08/09/2018 10:16 PM, Alan Braslau wrote:
> On Thu, 9 Aug 2018 22:00:48 +0200
> Pablo Rodriguez <oinos@gmx.es> wrote:
> 
>> I guess that backwards compatibility should be important here, but I
>> hope there are stronger reasons for breaking it.
> 
> tonumber() provides backwards compatibility. And the recommendation
> to use it was in the third edition (of the lua book), if not before,
> referring to 5.2.

I realize that the fault is mine, but with backwards compatibility I
meant that the same operation (10 + "10") gives different results with
different Lua versions.

Pablo
-- 
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Re: integer displayed as .0 float in Lua-5.3

[Alan Braslau]

On Sat, 11 Aug 2018 11:29:41 +0200
Pablo Rodriguez <oinos@gmx.es> wrote:

> On 08/09/2018 10:16 PM, Alan Braslau wrote:
> > On Thu, 9 Aug 2018 22:00:48 +0200
> > Pablo Rodriguez <oinos@gmx.es> wrote:
> >   
> >> I guess that backwards compatibility should be important here, but I
> >> hope there are stronger reasons for breaking it.  
> > 
> > tonumber() provides backwards compatibility. And the recommendation
> > to use it was in the third edition (of the lua book), if not before,
> > referring to 5.2.  
> 
> I realize that the fault is mine, but with backwards compatibility I
> meant that the same operation (10 + "10") gives different results with
> different Lua versions.
> 
> Pablo

"Bad" coding can be expected to give unpredictable results.

The creators of lua thought that automatic string conversion would be useful (and I believe that they got this feature from "awk", which itself may have gotten this from some previous scripting language). But they learned that automatic string conversion often creates more problems than it solves, so they recommend using explicit conversion through tonumber().

Lua is a very beautiful and powerful language, and it gives me surprises all of the time. Much of what Hans does I like to call "lua magic" meaning that I sort-of understand it but am impressed each time. Does this make lua a poor (problematic) scripting language? I think like all powerful tools, one must take care in their use.

Alan
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Re: integer displayed as .0 float in Lua-5.3

[Arthur Reutenauer]

On Sat, Aug 11, 2018 at 11:29:41AM +0200, Pablo Rodriguez wrote:
> I realize that the fault is mine, but with backwards compatibility I
> meant that the same operation (10 + "10") gives different results with
> different Lua versions.

  It doesn’t, it returns 10 in both cases.  The difference is in the
behaviour of the print function.  Try

	print(10.0)

in Lua 5.2 and 5.3: the former prints 10, the latter 10.0.  That is
consistent with the part of the specification you quote in another
email: in Lua >= 5.3, a number with a decimal point in it is always
interpreted as a float.  If the number to be printed is the result of
some computation, however (instead of lexical analysis), a choice needs
to be made: that is where the change occurred, since in Lua 5.2 print
displayed the shortest possible representation, while in Lua 5.3 it
chose to interpret the number as a float.  It’s a reasonable choice and
breaking compatibility for an elementary function such a print is to be
expected when such a change in the language occurred; even desirable, in
my opinion.

	Best,

		Arthur
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Re: integer displayed as .0 float in Lua-5.3

[Hans Hagen]

On 8/9/2018 10:00 PM, Pablo Rodriguez wrote:
> On 08/09/2018 09:34 PM, Alan Braslau wrote:
>> The lua manual also states that one should NOT rely on the implicit
>> conversion of a string to its numerical value, and suggests the
>> systematic use of tonumber().
> 
> Many thanks for your reply, Alan.
> 
> I guess that backwards compatibility should be important here, but I
> hope there are stronger reasons for breaking it.
> 
> Many thanks for your help,
In addition to what others already explained, you should not depend on 
features that are implementation dependent or might disappear. That said 
...

\startTEXpage[offset=1em]
\ctxlua{context([[\lastpage]])}.
\stopTEXpage

Why do you convert \lastpage to a string using [[\lastpage]] which will 
use the string to number conversion. In fact this automatic cast from 
string to number in an addition might disappear from the language in the 
future so don't rely on that.

You can just do:

\startTEXpage[offset=1em]
\ctxlua{context(\lastpage + 1)}.
\stopTEXpage

Or when in dount about what \lastpage is

\startTEXpage[offset=1em]
\ctxlua{context(\number\lastpage + 1)}.
\stopTEXpage

or if you really want to [[ ]]

\startTEXpage[offset=1em]
\the\numexpr\ctxlua{context([[lastpage]] + 1)}\relax .
\stopTEXpage

endless possibities here.

Hans


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Re: integer displayed as .0 float in Lua-5.3

[Pablo Rodriguez]

On 08/09/2018 10:25 PM, Hans Hagen wrote:
> In addition to what others already explained, you should not depend on 
> features that are implementation dependent or might disappear.

Many thanks for your detailed explanation, Hans.

I had no idea that the automatic conversion from string to number where
so dependent on the Lua version.

> That said 
> ...
> 
> \startTEXpage[offset=1em]
> \ctxlua{context([[\lastpage]])}.
> \stopTEXpage
> 
> Why do you convert \lastpage to a string using [[\lastpage]] which will 
> use the string to number conversion?

Well, I must confess that this is a new knowledge to me.

I thought that "[[ ]]" was the form to escape what I think it is the
escape character in Lua.

How I came to that assumption? Probably because I tried to add a raw
command to \ctxlua or inside a \startlua...\stoplua.

> You can just do:
> 
> \startTEXpage[offset=1em]
> \ctxlua{context(\lastpage + 1)}.
> \stopTEXpage

From this sample, I understand that "\" doesn’t need to be escaped
inside context(), does it?

> or if you really want to [[ ]]
> 
> \startTEXpage[offset=1em]
> \the\numexpr\ctxlua{context([[lastpage]] + 1)}\relax .
> \stopTEXpage
> 
> endless possibities here.

I don’t need "[[ ]]", I only thought I needed them.

Many thanks for your help,

Pablo
-- 
http://www.ousia.tk
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Re: integer displayed as .0 float in Lua-5.3

[Hans Åberg]

> On 9 Aug 2018, at 21:20, Pablo Rodriguez <oinos@gmx.es> wrote:
> 
>  A numeric constant with a radix point or an exponent denotes a
>  float; otherwise, if its value fits in an integer, it denotes an
>  integer.
> 
> Well, "10.0" contains the radix point, but with no arithmetical relevance.
> 
> My background is in humanities and I don’t understand the exponent for
> being a float ("10²" contains an exponent
> [https://www.m-w.com/dictionary/exponent], but I would say is an integer
> in all possible worlds [or all the worlds I know ]).
> 
> Could anyone explain me what am I missing here or confirm whether this
> is a bug?

It may refer to a floating point number syntax as in C++ [1], where the three cases top there say that there must be a point '.' preceded or followed by at least one digit, or at least one digit followed by an exponent starting with 'e' or 'E'. There are also some examples on that page. Also note that there are no negative numbers, which is because a leading + or - are treated as operators that apply not only to numbers.

1. https://en.cppreference.com/w/cpp/language/floating_literal


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Re: integer displayed as .0 float in Lua-5.3

[Pablo Rodriguez]

On 08/09/2018 10:20 PM, Hans Åberg wrote:
>> On 9 Aug 2018, at 21:20, Pablo Rodriguez wrote:
>> [...]
>> My background is in humanities and I don’t understand the exponent for
>> being a float ("10²" contains an exponent
>> [https://www.m-w.com/dictionary/exponent], but I would say is an integer
>> in all possible worlds [or all the worlds I know ]).
> 
> It may refer to a floating point number syntax as in C++ [1], where the
> three cases top there say that there must be a point '.' preceded or
> followed by at least one digit, or at least one digit followed by an
> exponent starting with 'e' or 'E'.

Many thanks for your explanation, Hans.

I thought there should be some kind of restriction when referring to the
exponent, but this is why technical explanations aren’t always very
clear. I mean, they have too many restrictions attached to them.

Pablo
-- 
http://www.ousia.tk
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Re: integer displayed as .0 float in Lua-5.3

[Hans Åberg]

> On 11 Aug 2018, at 11:33, Pablo Rodriguez <oinos@gmx.es> wrote:
> 
> On 08/09/2018 10:20 PM, Hans Åberg wrote:
>>> On 9 Aug 2018, at 21:20, Pablo Rodriguez wrote:
>>> [...]
>>> My background is in humanities and I don’t understand the exponent for
>>> being a float ("10²" contains an exponent
>>> [https://www.m-w.com/dictionary/exponent], but I would say is an integer
>>> in all possible worlds [or all the worlds I know ]).
>> 
>> It may refer to a floating point number syntax as in C++ [1], where the
>> three cases top there say that there must be a point '.' preceded or
>> followed by at least one digit, or at least one digit followed by an
>> exponent starting with 'e' or 'E'.
> 
> Many thanks for your explanation, Hans.

You are welcome.

> I thought there should be some kind of restriction when referring to the
> exponent, but this is why technical explanations aren’t always very
> clear. I mean, they have too many restrictions attached to them.

The C++ description allows for fast reading with just one lookahead character at a time, which is was important in C when it appeared in 1972 on the not so powerful computers of the day.

Then roundoff may make floating point numbers look like integers even they are not. For example, 1.0 could be 0.99999999 or 1.0000001.

So don't check floating numbers for equality, instead use say abs(x - y) < a for some small number a.

When adding exact integers and inexact floating point numbers, it is easiest to always make that inexact numbers, as exactness cannot always be guaranteed.


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Re: integer displayed as .0 float in Lua-5.3

[Hans Hagen]

On 8/11/2018 11:33 AM, Pablo Rodriguez wrote:
> On 08/09/2018 10:20 PM, Hans Åberg wrote:
>>> On 9 Aug 2018, at 21:20, Pablo Rodriguez wrote:
>>> [...]
>>> My background is in humanities and I don’t understand the exponent for
>>> being a float ("10²" contains an exponent
>>> [https://www.m-w.com/dictionary/exponent], but I would say is an integer
>>> in all possible worlds [or all the worlds I know ]).
>>
>> It may refer to a floating point number syntax as in C++ [1], where the
>> three cases top there say that there must be a point '.' preceded or
>> followed by at least one digit, or at least one digit followed by an
>> exponent starting with 'e' or 'E'.
> 
> Many thanks for your explanation, Hans.
> 
> I thought there should be some kind of restriction when referring to the
> exponent, but this is why technical explanations aren’t always very
> clear. I mean, they have too many restrictions attached to them.
small numbers can get expresses in nEm notation instead of 0.00000... 
which can also bite you (in context we intercept this when needed)

Hans

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