On Sat, Feb 18, 2012 at 09:02:41PM -0500, Stephen Bloch wrote:
[...]
> I see a lot of my students doing this -- in whatever language -- because they
> think of Booleans as a way to decide which of two things to DO, rather than
> as legitimate values in their own right. In fact, the whole world of
> expressions is a bit of a foreign country -- a sort of "adjunct" to the
> more-legitimate world of statements.
>
> if (blah == true) {
> return true;
> }
> else {
> return false;
> }
Yes, I talked with my 3rd-year PL students about this, with examples in Racket.
Then an assignment had them take what I called "Π-expressions [s-expressions
representing Python code, spit out by a little Python programm walking an AST
produced by complier.ast], and find exactly those two style issues above [and
also string literals "True"/"False", which 1st-years are using for booleans,
and then it occurred to us that identifier 'true' is a common problem due to
Python's not quite fully lexical scoping]. Yet some students still used these
forms in earlier parts of the assignment and didn't notice nor remember and
go back [at least the ones I trust not to claim that instead of laziness]!
>
> For those of us forced to teach in Java, CheckStyle has two modules,
> SimplifyBooleanExpression and SimplifyBooleanReturn, that catch things like
> this.
>
>
> Stephen Bloch
> sbl...@adelphi.edu
Python's PEP 8 style guide mentions the comparison problem, but only "== True"
and "is True": nothing about inequality nor false literal, and not selection.
http://www.python.org/dev/peps/pep-0008/
On a more productive note: in Racket code I define and use 'implies' a lot,
often conjoined, for predicates. It's mainly of declarative value, which is
perhaps why it's uncommon in implementation despite how common it is in
specification. And for boolean expressions in general I also use 'neither'.
Are these something that others [would] use and so could be added to Racket's
library?
____________________
Racket Users list:
http://lists.racket-lang.org/users
