[erlang-bugs] Parser bug: if missing ", " in list between records, the first is ignored, and no parser warnings are given.

[Roland Karlsson]

On Sat, 8 Nov 2014 09:02:08 +0100
Mattias Waldau <mattias.waldau@REDACTED> wrote:

> Yes, I can agree that
> 
> #rec{a=2}#rec{b=3}
> 
> is a matter of opinion. However, I completely fail to understand how
> 
> #rec{a=2}#rec{a=3}
> 
> can be a matter of opinion, since data in the code is LOST.

Data is not lost.
The code creates a record rec with the field a being 2.
Then the code creates a copy of that record where the field now is 3.
The first record is instance not used though. But, as it has no name
that usually do not give a warning in Erlang, just like unused variables
with underscore names do not give a warning.

But ... I can see why it might maybe be a warning there.
It IS a matter of opinion though IMHO.

You have to be aware of the following code though.

(?MY_DEF_REC)#rec{a=3}

Lets say the macro MY_DEF_REC creates a record rec with some
special default values. Lets say that one of the fields you have a
special default value for is a. Do you want a warning?


/Roland








> There should be a warning. My sample below shows how catastropic the missing "," can be.
> 
> /mattias
> 
> On 07/11/2014 13:22, Roland Karlsson wrote:
> > Maybe we shall not discuss this for ever :)
> > It is a matter of opinion after all.
> >
> > But - it is the same IMHO. It is a matter of operators and the need
> > to set paranthesis when the precedents and right/left association is
> > not obvious.
> >
> > The rec example can be written thus
> >
> > (#rec{a=2})#rec{b=3}
> >
> > Then everything is clear.
> >
> >
> > /Roland
> >
> >
> >
> >> I'm not sure how that relates. This expression can be reasonably written
> >> on purpose. The same cannot be said for #rec{a=2}#rec{b=3}.
> >>
> >> On 11/07/2014 02:01 PM, Roland Karlsson wrote:
> >>> If there is a warning there, then all expressions including operators,
> >>> e.g. arithmetic, should have warnings. How about 10 + 1 rem 3 + 7. ?
> >>> Do you know the precedence of + and rem ? What is the result?
> >>>
> >>> /Roland
> >>>
> >>>
> >>>
> >>>> Warnings are ordinary Erlang code which is prone to errors.
> >>>>
> >>>> On 11/07/2014 01:46 PM, Roland Karlsson wrote:
> >>>>> No warning is needed methinks. It is just ordinary Erlang code.
> >>>>> It is equal to.
> >>>>>
> >>>>>> REC1 = #rec{b=3}.
> >>>>>> REC2 = REC1#rec{a=2}.
> >>>>> Nothing strange at all.
> >>>>>
> >>>>>
> >>>>> /Roland
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>> It is legal but there probably should be a warning for this
> >>>>>> particular
> >>>>>> case. I cannot think of a valid reason to do #rec{a=2}#rec{b=3} when
> >>>>>> you
> >>>>>> can just do #rec{a=2, b=3}.
> >>>>>>
> >>>>>> On 11/07/2014 10:09 AM, Vlad Dumitrescu wrote:
> >>>>>>> Hi Mattias,
> >>>>>>>
> >>>>>>> This isn't a bug. The expression #rec{a=2}#rec{b=3} is legal, and is
> >>>>>>> the
> >>>>>>> same thing as (#rec{a=2})#rec{b=3} or #rec{a=2,b=3}. If the keys
> >>>>>>> overlap, then the last one "wins".
> >>>>>>>
> >>>>>>> best regards,
> >>>>>>> Vlad
> >>>>>>>
> >>>>>>>
> >>>>>>> On Thu, Nov 6, 2014 at 9:21 AM, Mattias Waldau
> >>>>>>> <mattias.waldau@REDACTED <mailto:mattias.waldau@REDACTED>>
> >>>>>>> wrote:
> >>>>>>>
> >>>>>>>        This is the program
> >>>>>>>
> >>>>>>>        -module('missing-comma-not-detected').
> >>>>>>>
> >>>>>>>        -export([data/1]).
> >>>>>>>
> >>>>>>>        -compile(export_all).
> >>>>>>>
> >>>>>>>        -record(shcnode, {
> >>>>>>>               nodename :: any(),
> >>>>>>>               y_axis :: number(),
> >>>>>>>               children :: [any()],
> >>>>>>>               article_number :: number(),
> >>>>>>>               attribute_condition :: string()}).
> >>>>>>>
> >>>>>>>
> >>>>>>>        data(1) ->
> >>>>>>>             [
> >>>>>>>              #shcnode{nodename = start, y_axis = 0, children =
> >>>>>>> [d1285]},
> >>>>>>>              #shcnode{nodename = d1285, y_axis = 295, children =
> >>>>>>> [1939,
> >>>>>>> 1940]}
> >>>>>>>              #shcnode{nodename = 1940, y_axis = 525, children =
> >>>>>>> [bm3203],
> >>>>>>>        article_number = 14432861},
> >>>>>>>              #shcnode{nodename = 1939, y_axis = 530, children =
> >>>>>>> [bm3203],
> >>>>>>>        article_number = 14432860},
> >>>>>>>              #shcnode{nodename = bm3203, y_axis = 915, children = []}
> >>>>>>>             ].
> >>>>>>>
> >>>>>>>
> >>>>>>>        Note the missing "," after  [1939, 1940]}
> >>>>>>>
> >>>>>>>        Only 4 rows are detected
> >>>>>>>
> >>>>>>>        length('missing-comma-not-detected':data(1)).
> >>>>>>>        4
> >>>>>>>
> >>>>>>>        ---
> >>>>>>>
> >>>>>>>        If I add the comma, I get
> >>>>>>>
> >>>>>>>        length('missing-comma-not-detected':data(1)).
> >>>>>>>        5
> >>>>>>>
> >>>>>>>        ----
> >>>>>>>
> >>>>>>>        I am using Erlang 17.3 on ubuntu.
> >>>>>>>
> >>>>>>>        erlang:system_info(otp_release).
> >>>>>>>        "17"
> >>>>>>>
> >>>>>>>        36> |erl -V
> >>>>>>>        Eshell V6.2  (abort with ^G)
> >>>>>>>        1> |
> >>>>>>>
> >>>>>>>        ---
> >>>>>>>
> >>>>>>>        Thanks,
> >>>>>>>
> >>>>>>>        Mattias
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>        _______________________________________________
> >>>>>>>        erlang-bugs mailing list
> >>>>>>>        erlang-bugs@REDACTED <mailto:erlang-bugs@REDACTED>
> >>>>>>>        http://erlang.org/mailman/listinfo/erlang-bugs
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> _______________________________________________
> >>>>>>> erlang-bugs mailing list
> >>>>>>> erlang-bugs@REDACTED
> >>>>>>> http://erlang.org/mailman/listinfo/erlang-bugs
> >>>>>>>
> >>>>>> --
> >>>>>> Loïc Hoguin
> >>>>>> http://ninenines.eu
> >>>>>> _______________________________________________
> >>>>>> erlang-bugs mailing list
> >>>>>> erlang-bugs@REDACTED
> >>>>>> http://erlang.org/mailman/listinfo/erlang-bugs
> >>>>>>
> >>>>>
> >>>> --
> >>>> Loïc Hoguin
> >>>> http://ninenines.eu
> >>>>
> >>>
> >> --
> >> Loïc Hoguin
> >> http://ninenines.eu
> >> _______________________________________________
> >> erlang-bugs mailing list
> >> erlang-bugs@REDACTED
> >> http://erlang.org/mailman/listinfo/erlang-bugs
> >>
> >
> 
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-- 
Roland Karlsson <roland.karlsson@REDACTED>