[erlang-questions] DRY principle and the syntax inconsistency in fun vs. vanilla functions

[Parnell Springmeyer]

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Sorry, but Erlang doesn't *need* a better chance of survival. This
language is not just growing, it's booming. Changing core language
features that are solid, well thought out, and non-harmful (in other
words, they are, FEATURES) to make it more "adoptable" is a lot like
someone saying, "you have to quit that quirky smile so other people will
like you more."

Sometimes, yes, there are features in a language that could use
refinement - but many times, in a mature language, the ratio between
need and usefulness in refining a feature further, drops significantly.

Instead of changing something that is solid, educate the people that
have a hard time grasping it, build killer example applications that
exhibit the quirky style and idioms to a T - people /will/ follow it,
almost to a religious end.

That's actually what I like about Erlang the most, the documentation has
so many gems in it like the efficiency guide (where many common idioms
are expressed with clear DO and DON'T DO examples) and style guide.

RE: syntactic consistency: Erlang's syntax *IS* consistent - it's more
consistent than many languages I've touched.

Is Erlang easy for a Perl programmer? I bet not, and Perl's syntax is
less consistent than Erlang's is in my opinion. The issue you are
attempting to get at is (again) an educational and experience one, not
something that is inherently wrong with the language or its expression
itself.

I'm actually baffled by the efforts people are putting into different
Erlang VM frontends that look like Ruby or Python. Good on them for
exercising the freedom of open source but /why/? Erlang's syntax is
almost beautiful to me now after using it, it's so well suited for what
Erlang is good at!

Erlang isn't that great for general purpose programming - you use
Python, Ruby, C, D, etc... for stuff like that. Erlang is great at fault
tolerance, easy parallelism (which isn't easy!), and hot code
loading. Features that are so difficult to do in the traditional
imperative environment that (to date) I have not seen a single
implementation of any one of those features that even approaches the
completeness of Erlang's.

Michael Turner <michael.eugene.turner@REDACTED> writes:

> Another objection raised against this syntax change is that all
> functional languages violate DRY in this manner, so it's OK if Erlang
> does it too. This is a Principle of Least Surprise argument, and not
> bad as far as it goes. But how far does it go?
>
> Erlang will have a better chance of greater success and survival if you
> consider your recruitment base to be the overwhelming majority of
> programmers. And from what I can tell,
>
>   http://www.langpop.com
>
> the overwhelming majority of programmers have no experience to speak
> of, when it comes to functional programming languages. Appealing to the
> "cross-training" benefit of coming from other FP languages seems like a
> pretty weak argument. Especially since all I'm asking for here is
> syntactic consistency *within* Erlang -- a PLoS argument in itself.
>
> Richard O'Keefe suggests that the syntactic consistency goal is better
> met by allowing a kind of limited-scope special-case fun name,
> permitting, e.g.
>
>   Fact = fun F(0) -> 1; F(N) -> N*F(N-1) end.
>
> I could get behind that too, but I don't follow his reasoning from
> syntactic consistency, which is apparently that an unnamed fun has a
> name, it's just the degenerate case of a name.  It's really there. We
> just can't see it. Hm, really? If that were true in Erlang as it
> stands, shouldn't I be able to write it this way?
>
>   Fact = fun (0) -> 1; (N) -> N*''(N-1) end.
>
> Looks like it's not quite that simple. It compiles, but it doesn't know
> what module to look in for '', when it comes time to execute. In the
> shell, I get an error indicating that it tried to resolve ''/1 as a
> shell command. Even if I put it in a .erl file and compile it, there's
> no obvious way to tell the compiler what module to look in. ?MODULE:''
> doesn't work. Nor does '':'', which I tried just for the hell of it.
>
> What Richard's suggesting appears to require a rigorous re-think of how
> scopes are defined in Erlang. What I'm suggesting amounts to simply
> asking the compiler to do some of your tedious keying for you.
>
> -michael turner
>  
>
> On Wed, May 18, 2011 at 6:16 PM, Michael Turner <
> michael.eugene.turner@REDACTED> wrote:
>
>     I can say
>    
>        fun (1)->2;
>             (2)->1
>        end
>    
>     but, oddly, I can't define a named function in the analogous way,
>     e.g.:
>    
>        factorial
>          (1) -> 1;
>          (N) -> N*factorial(N-1).
>    
>     gives me a syntax error. I find the latter more readable than
>    
>        factorial(1) -> 1;
>        factorial(2) -> N*fact(N-1).
>    
>     It's also less to type and to read, which is consistent with the
>     DRY principle ("Don't Repeat Yourself").  And it lends itself to
>     reading a function definition as a set of cases. I think for Erlang
>     newbies, it should therefore would be preferred: it helps
>     underscore the pattern-matching style of Erlang function
>     invocation.
>    
>     It also looks a *little* bit more like the mathematical convention
>     for defining these sorts of functions, where you have "f(x) = ",
>     centered vertically to the left of a big left "{" that (left-)
>     encloses the list of expression/parameter-condition pairs in a
>     two-column format, e.g.,
>    
>      http://cnx.org/content/m29517/latest/Picture%2047.png
>    
>     So there's a (weak) argument from the Principle of Least Surprise
>     here as well.
>    
>     It seems to me that, if anything, this requires only a
>     *simplification* of the Erlang parser. That leaves only one obvious
>     objection: would any existing code break if Erlang syntax were
>     altered to allow this?
>    
>     -michael turner
>
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- -- 
Parnell "ixmatus" Springmeyer (http://ixmat.us)
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