RE: st: RE: Equals: why the "=" (attribution) vs. "==" (Boolean) syntax distinction ???

[Joe Canner <jcanner1@jhmi.edu>]

As a former SAS programmer, I still forget the == on a regular basis and you are right that the error messages for this situation are inconsistent and uninformative.  I'm sure there are good historical and logical reasons for the error messages, but it would sure help the beginning programmer if they were better.

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Lucas Ferreira Mation
Sent: Tuesday, August 27, 2013 2:59 PM
To: statalist
Subject: Re: st: RE: Equals: why the "=" (attribution) vs. "==" (Boolean) syntax distinction ???

Joe, Nick, tks for the feedback on this. Personally I also don´t mind the distinction.

on "gen a=b==c" : is this the only case (and is a particular syntax of
gen) where the situation is slightly ambiguous?   Even in this case,
the precedence of the attribution equal makes it unambiguous. Or the syntax of this specific command could make parenthesis  mandatory, ex:
"gen a=(b=c)".

If this is the only case, and all other commands have conditions after the "if",  why bother? I agree the similarity with other languages is an advantage. However, in less "regular" languages, like R this, a==b vs. a=b distinction is necessary, but in Stata the language is so regular that there is not much room for confusion.


I don´t have data on mistakes, I was (imprecisely) referring to my impressions from teaching a few courses and also from my own learning curve. I never counted, but this is definitively the most frequent mistake students make (the other very common is forgetting to wrap strings in " ", gen x=blab).

In this last course there were 3 types of students:
- non programmers (excel, spss, ...): were puzzled by the conceptual distinction, but got used to it.
- SAS programmers : in general were amazed by Stata syntax, to the point of almost converting. But then got annoyed with this "=" vs.
"==" distinction. And complained that error messages in Stata are uninformative and Stata is difficult do debug.
- a few R programmers: were fine, and happy to have "less options".
One or two ways to do things instead of 10 different ways in R.

anyway, tks for the feedback and an interesting discussion regards Lucas

On Tue, Aug 27, 2013 at 3:05 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> Agreed on the major point that == are standards across many languages.
>
> The last FWIW is a standard Mata device. Those who use it wouldn't 
> call it obscure, although it's the sort of thing that should make you 
> slow right down when reading it.
>
> More generally, no one delights that Stata syntax can be tricky, but 
> you can't have a rich language without the possibility that it's not 
> all transparent to the beginning user.
> Nick
> njcoxstata@gmail.com
>
>
> On 27 August 2013 18:56, Joe Canner <jcanner1@jhmi.edu> wrote:
>> It's also worth pointing out that using == for Boolean comparison is common in other programming languages.  This doesn't help the beginning Stata user who isn't also a programmer, but it does help those who move around between different languages.
>>
>> There are some languages (mostly older) that do not make this distinction, but in these languages you lose the flexibility of being able to do a Boolean comparison on the right side of an assignment statement.  When memory and/or CPU cycles are at a premium this can be an important issue.
>>
>> FWIW, some languages (not sure about Stata) also allow an assignment = in an -if- statement, e.g. if (x=y+z) {...}.  In this case, TRUE is returned if the assignment is performed without error and FALSE otherwise.  This is an obscure, but occasionally useful, usage which contributes to code flexibility and programmer happiness.
>>
>> -----Original Message-----
>> From: owner-statalist@hsphsun2.harvard.edu 
>> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
>> Sent: Tuesday, August 27, 2013 1:25 PM
>> To: statalist@hsphsun2.harvard.edu
>> Subject: Re: st: RE: Equals: why the "=" (attribution) vs. "==" (Boolean) syntax distinction ???
>>
>> Not without a little sympathy, but....
>>
>> It's for Stata's convenience, which ultimately means yours too. As = means assignment and == asserts equality,  Stata needs a way of keeping them straight.
>>
>> As Joe implies, the alternative is some rule that tells you that = 
>> means one thing in one place and another thing in another place. It's 
>> not clear to me that anyone who gets tripped up by existing syntax 
>> would not get tripped up by that. ("The first = means this, but the 
>> second has a _quite_ different meaning....")
>>
>> I've also encountered many positive reactions to this syntax when users see that Stata is making a logical distinction between logically different things.
>>
>> Perhaps here the taste and logic of the language designer seem to be triumphing over the taste and convenience of the beginning user, but that's the way it goes. Heck, more advanced users have some rights too!
>>
>> I didn't know there were hard data anywhere on frequency of users' mistakes.
>>
>>
>> Nick
>> njcoxstata@gmail.com
>>
>>
>> On 27 August 2013 18:10, Joe Canner <jcanner1@jhmi.edu> wrote:
>>> How about the following?
>>>
>>> . gen a=b==c
>>>
>>> How would Stata interpret this (valid) statement if there was no distinction between = and ==?
>>>
>>> -----Original Message-----
>>> From: owner-statalist@hsphsun2.harvard.edu
>>> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Lucas 
>>> Ferreira Mation
>>> Sent: Tuesday, August 27, 2013 1:00 PM
>>> To: statalist
>>> Subject: st: Equals: why the "=" (attribution) vs. "==" (Boolean) syntax distinction ???
>>>
>>> sort of a philosophical question (and I could not find any previous discussion on this topic in the list):
>>>
>>> why does Stata the language differentiate between "=" and "==" ?
>>>
>>> I was teaching a Intro to Stata Class and the students were asking about it. I explained the difference between attribution equal (=) and Boolean check equal (==).
>>>
>>> Although they got the concept, the question remains:
>>>
>>> why be explicit about this distinction in the language syntax?
>>>
>>> Thinking about it, it seems to me that the occurrences of "equal"
>>> (attribution vs. Boolean) aways appear in distinct places in the syntax, so it does not seem prone to mistakes.
>>>
>>> On the other hand, forgetting "==" it the single most common mistake beginner users make, and even more advanced users ofter forget.
>>>
>>> Anyway, I just wanted to know if there are other reasons I'm unaware of.
>>>
>>>
>>> Lucas
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