Re: [PATCH] More correctly describe the scope of variables

[Jouke Witteveen]

On Fri, Dec 25, 2020 at 7:58 PM Pete Dietl <petedietl@gmail.com> wrote:
> Now for Make, there are no semantics for telling whether or not it is 
> lexically or dynamically scoped. This is because previously the only local 
> variables were the function arguments. Since these arguments are always named 
> the same thing, even if the language were dynamically scoped, successive 
> function calls would create new function argument variables which shadow the 
> previous ones. If you try to use eval to create functions or variables on the 
> fly, it works but both are added to the global scope.

There is an easy demonstration (adapted from
https://en.wikipedia.org/wiki/Scope_(computer_science) ):
----
x=1
g=$(info $x)
f=$(foreach x,3,$g)
$f
$(info $x)
----
Here, `foreach` can be replaced by `let`. The first output is "3",
demonstrating dynamic scoping.
Behavior aside, the source code of GNU make is structured so that make
has dynamic scoping.

Apart from these remarks, I agree with your analysis and have also
observed that assignments in $(eval) will assign at the global scope
(and not the scope at the top of the stack). I am not sure whether
that is a feature or a bug.

Regards,
- Jouke

>
> On Fri, Dec 25, 2020 at 10:00 AM Jouke Witteveen <j.witteveen@gmail.com> 
> wrote:
>>
>> * NEWS: Use "local" instead of the incorrect "lexically-scoped".
>> * doc/make.texi: Refer to let/foreach variables as local variables.
>> ---
>> This is an erratum on the addition of $(let ...). During an early review
>> of $(let ...), thutt cautioned that it did not implement "full semantic
>> scoping" [sic]. While I did not understand fully what they meant by
>> that, I countered that it was not intended to determine a scope based on
>> for example which file a definition of a rule occurred in, but simply by
>> the parentheses delimiting the let expression. Only in that sense was it
>> lexical scoping. Technically, make variables are dynamically scoped.
>>
>> This patch replaces "lexically scoped" not by "dynamically scoped", but
>> by "local", since that is the whole point after all. It also includes
>> variables with local scope (from let and foreach) in several other
>> places where variables are discussed, and makes explicit that variables
>> in make are dynamically scoped.
>>
>>  NEWS          |  4 ++--
>>  doc/make.texi | 21 +++++++++++++++------
>>  2 files changed, 17 insertions(+), 8 deletions(-)
>>