Hacker News Reader

Comment by fogus | Hacker News Reader

I may have missed the point, but it seems to me that the gist of the post is, "Perl 6 is different because it's the same as Lisp".

View on HN

I think you missed the point. The point is that Perl 6's "rules and grammars" are a profound innovation that will affect the future of language design.

I recognize that's the point the author made, I'm just not convinced of it. Show me the power through code. Right now it's just words.

As far as I can tell grammars are a way of organizing a bunch of regexes together so you can run them against a document to match and extract all the data. It might make it easier to write parsers but that is a small, though admittedly annoying, subset of programming problems. It doesn't seem like a general enough feature to qualify as "profound".

Parsers are already fairly easy to write in lispy languages. They just have a different name in that context -- "recursive functions".

Pick a famous computer scientist, and the odds are better than even they've written a paper or two on this topic.

I have no idea what you've just said, but it doesn't make any sense.

Of course parsers are described by recursive functions, that's because recursive functions usually describe a push-down automata or a DFA, which you know, is needed for a parser.

But describing a parser is not easy, even in lispy languages ... you still need a declarative syntax (like BNF or PEGs) for those rules, you still need a strategy (like LL(*) or LALR(1)), you still need to deal with context-dependent constructs, and you still need an AST that must be optimized.

Text parsing is also not one of Lisp's strengths. Many implementations don't even have proper regexp engines ... but indeed, it's easy to translate any language to LISP as long as you're goal is not to generate something human readable.

Lisp has portable libraries for regular expressions.

Like this one: http://weitz.de/cl-ppcre/

Thanks for the downvote ... I was more interested in what you meant in your comment, rather than proving me wrong about regexp engines.

Larry Wall himself said that:

Perl 6 is Lisp with a decent syntax, and minus a lot of assumptions about how lists should be represented :)

ref: http://irclog.perlgeek.de/perl6/2010-01-15#i_1905210

He then goes onto to mention that despite all the trappings of OO, Perl 6 is fundamentally more in the FP camp

LWall > Lisp with a decent syntax

I'm no Lisp guru, not even proficient but isn't saying that kind of missing a large point of Lisp in that code is data and data is a list/sexpresion or what ever it's called?

I think the point is "with rules you don't need everything to be and s-expression". I don't know how much to agree or not with that point. Currently I'm of the we'll see where is goes point of view.

> "with rules you don't need everything to be and s-expression"

I am unsure if I would call it a feature.

From a Perl point of view, I think it's the right way to go. There are a few "standard" tricks to simulate extending Perl5, but they often feel hackish. From my understanding this will be more flexible and explicit. I don't have the Lisp experience to compare the two. My guess is Lisp macros will still be more flexible but the gap will be significantly narrowed.

"Perl 6 is Lisp with a decent syntax,"

Calling perl syntax "decent", and by implication better than lisp syntax (such as there is) is mind bending.

Perl has a lot of syntax, and Lisp has almost none. Which one is better just depends on your opinion about syntax itself.

Lisp also has a lot of syntax, but it is ON TOP of s-expressions.

Hold Common Lisp next to Perl 5, and you tell me which one has "a lot" of syntax.

I realize that Lisp has some syntax, and of course the fact that everything fits into S-exps is important, but I would not say that it has "a lot" of syntax compared to the vast majority of active languages.

Let's just look at the syntax of Common Lisp's LOOP construct:

    loop [name-clause] {variable-clause}* {main-clause}* => result*

    name-clause::= named name 
    variable-clause::= with-clause | initial-final | for-as-clause 
    with-clause::= with var1 [type-spec] [= form1] {and var2 [type-spec] [= form2]}* 
    main-clause::= unconditional | accumulation | conditional | termination-test | initial-final 
    initial-final::= initially compound-form+ | finally compound-form+ 
    unconditional::= {do | doing} compound-form+ | return {form | it} 
    accumulation::= list-accumulation | numeric-accumulation 
    list-accumulation::= {collect | collecting | append | appending | nconc | nconcing} {form | it}  
                         [into simple-var] 
    numeric-accumulation::= {count | counting | sum | summing | } 
                             maximize | maximizing | minimize | minimizing {form | it} 
                            [into simple-var] [type-spec] 
    conditional::= {if | when | unless} form selectable-clause {and selectable-clause}*  
                   [else selectable-clause {and selectable-clause}*]  
                   [end] 
    selectable-clause::= unconditional | accumulation | conditional 
    termination-test::= while form | until form | repeat form | always form | never form | thereis form 
    for-as-clause::= {for | as} for-as-subclause {and for-as-subclause}* 
    for-as-subclause::= for-as-arithmetic | for-as-in-list | for-as-on-list | for-as-equals-then | 
                        for-as-across | for-as-hash | for-as-package 
    for-as-arithmetic::= var [type-spec] for-as-arithmetic-subclause 
    for-as-arithmetic-subclause::= arithmetic-up | arithmetic-downto | arithmetic-downfrom 
    arithmetic-up::= [[{from | upfrom} form1 |   {to | upto | below} form2 |   by form3]]+ 
    arithmetic-downto::= [[{{from form1}}1  |   {{{downto | above} form2}}1  |   by form3]] 
    arithmetic-downfrom::= [[{{downfrom form1}}1  |   {to | downto | above} form2 |   by form3]] 
    for-as-in-list::= var [type-spec] in form1 [by step-fun] 
    for-as-on-list::= var [type-spec] on form1 [by step-fun] 
    for-as-equals-then::= var [type-spec] = form1 [then form2] 
    for-as-across::= var [type-spec] across vector 
    for-as-hash::= var [type-spec] being {each | the}  
                   {{hash-key | hash-keys} {in | of} hash-table  
                    [using (hash-value other-var)] |  
                    {hash-value | hash-values} {in | of} hash-table  
                    [using (hash-key other-var)]} 
    for-as-package::= var [type-spec] being {each | the}  
                      {symbol | symbols | 
                       present-symbol | present-symbols | 
                       external-symbol | external-symbols} 
                      [{in | of} package] 
    type-spec::= simple-type-spec | destructured-type-spec 
    simple-type-spec::= fixnum | float | t | nil 
    destructured-type-spec::= of-type d-type-spec 
    d-type-spec::= type-specifier | (d-type-spec . d-type-spec) 
    var::= d-var-spec 
    var1::= d-var-spec 
    var2::= d-var-spec 
    other-var::= d-var-spec 
    d-var-spec::= simple-var | nil | (d-var-spec . d-var-spec)

I don't think there are many active languages with a more complex LOOP construct. Add to that, that some implementations have an extensible LOOP that allows to add even more syntax to it.

The syntax for DEFCLASS:

    defclass class-name ({superclass-name}*) ({slot-specifier}*) [[class-option]]

    => new-class

    slot-specifier::= slot-name | (slot-name [[slot-option]])
    slot-name::= symbol
    slot-option::= {:reader reader-function-name}* | 
                   {:writer writer-function-name}* | 
                   {:accessor reader-function-name}* | 
                   {:allocation allocation-type} | 
                   {:initarg initarg-name}* | 
                   {:initform form} | 
                   {:type type-specifier} | 
                   {:documentation string} 
    function-name::= {symbol | (setf symbol)}
    class-option::= (:default-initargs . initarg-list) | 
                    (:documentation string) | 
                    (:metaclass class-name)

there is much more of this.

LOOP is a good example of syntax creeping its way into Lisp (defclass, not all that much IMO).

As a counterexample that almost makes LOOP syntax look quaint, consider Perl regexes. That is some syntax right there.

Common Lisp has more than 30 special syntactic constructs: block, catch, eval-when, LET, ..., unwind-protect.

It has probably more than a hundred macros that implement syntax: DEFUN, LOOP, DEFMACRO, WITH-OPEN-FILE, DEFPACKAGE, PPRINT-LOGICAL-BLOCK, HANDLER-CASE, ...

It has various basic syntactic elements like function lambda lists, macro lambda lists, etc.

It has FORMAT string syntax.

I'm not trying to win a contest with PERL and its syntax, but thinking that Common Lisp has almost no syntax is misguided. As I mentioned, in Common Lisp much of the syntax is implemented on top of s-expressions.

Stuff like regexp syntax is implemented in Common Lisp libraries. Like this one: http://weitz.de/cl-ppcre/ .

Perl's syntax is designed to be more close to natural language.

Both Lisp and Perl are in the same camp ... I could hardly read an algorithm written in them before learning and actively working with them.

Either way, I'm tired of languages that can only be extended by adding functions. Declarative APIs require much more than that.

> Perl's syntax is designed to be more close to natural language.

s/natural/English/. Some languages can be parsed by computer without problems. For example, simple 15kb C program can parse 100% of technical text in Esperanto, 98% of technical text in Ukrainian (my native language), 84% of technical text in Russian, and so on. Not so simple parser can parse more than 100% of text, i.e. it can fix errors in text.

For me, shell is much closer to my native language than perl or SQL.

PS. AFAIK, there is no natural language in the wild nature. :-/ All human languages are artificial.

I think bad_user might be referring to Larry Wall's post Natural Language Principles in Perl

ref: http://www.wall.org/~larry/natural.html

Whatever Larry is smoking, I don't want it.

I'm also not sure if that will help Perl 6.

Reply on news.ycombinator.com