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digitalmars.D - Why is C++ so hard to parse?

reply Pete <Pete_member pathlink.com> writes:
Hi,

I don't know much about parsing programming language. But I want to know what
makes C++ hard to parse and does D these things right?
Jan 26 2005
next sibling parent reply Dejan Lekic <leka entropy.tmok.com> writes:
Pete, IMHO C++ is not harder to parse than any other modern language,
including D.

-- 
...........
Dejan Lekic
  http://dejan.lekic.org
Jan 26 2005
next sibling parent reply Pete <Pete_member pathlink.com> writes:
Pete, IMHO C++ is not harder to parse than any other modern language,
including D.



A large C++ project here takes mor then three minutes for a complete
re-compilation. An even larger C# project takes only a few seconds. This isn't
C# specific. Java is as fast.
I did only some _very_ small D programs (if you want to call them programs), so
I don't know how fast D will compile.
Jan 26 2005
parent Dejan Lekic <leka entropy.tmok.com> writes:
"Parsing process" != "Compilation (build process)"

-- 
...........
Dejan Lekic
  http://dejan.lekic.org
Jan 26 2005
prev sibling parent "Walter" <newshound digitalmars.com> writes:
"Dejan Lekic" <leka entropy.tmok.com> wrote in message
news:ct839i$1iqj$1 digitaldaemon.com...

 Pete, IMHO C++ is not harder to parse than any other modern language,
 including D.



I've written a parser for both C++ and D. C++ is a lot harder. In fact, C++
is probably the most difficult computer language to parse. D is one of the
easier ones.
Jan 26 2005
prev sibling next sibling parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Pete wrote:

 Hi,
 
 I don't know much about parsing programming language. But I want to know what
 makes C++ hard to parse



Basically, the places where C++ grammar isn't context-free:

- cast expressions
- template syntax
- preprocessor macros to twist the syntactical structure
- probably other things....

This means that before C++ can parse something, it must know what the 
identifiers in it refer to.  Consequently, to write a properly-working 
C++ parser, you almost have to go the whole hog and write a compiler. 
Consequently, writing code manipulation tools (syntax-directed editors, 
beautifiers, linters, whatever) becomes tricky.

Moreover, parsing engines/parser generators such as yacc expect a 
context-free grammar.  Maybe it's possible using lex/yacc to manipulate 
the lexer as part of the parsing process, but it must be quite hard to do.


 and does D these things right?



Yes, modulo a few bugs and one legacy waiting to be thrown out.

The benefits of context-free grammar don't end there.  For example, I 
think the ability to pre-parse is one thing enabling D to gradually 
eliminate forward declarations.

Stewart.

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Jan 26 2005
parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Stewart Gordon wrote:
<snip>

 The benefits of context-free grammar don't end there.  For example, I 
 think the ability to pre-parse is one thing enabling D to gradually 
 eliminate forward declarations.



JTAI, there is at least one bit of C++ that supports forward 
referencing.  Not to mention Java, which has some of the 
non-context-free grammar from C++.

But still, no doubt context-free grammar considerably simplifies the 
process of supporting forward referencing....

Stewart.

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Jan 26 2005
parent reply "Regan Heath" <regan netwin.co.nz> writes:
On Wed, 26 Jan 2005 16:11:05 +0000, Stewart Gordon <smjg_1998 yahoo.com>  
wrote:

 JTAI



I hadn't seen this one before, and googling for it didn't help initially :)

http://www.google.com/search?q=JTAI&sourceid=opera&num=0&ie=utf-8&oe=utf-8
  - "Jewish Teen Arts Institue"

I now know it means - "Just Thinking About It"

Regan
Jan 26 2005
parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Regan Heath wrote:

 On Wed, 26 Jan 2005 16:11:05 +0000, Stewart Gordon 
 <smjg_1998 yahoo.com>  wrote:
 

 JTAI



 I hadn't seen this one before, and googling for it didn't help initially :)
 
 http://www.google.com/search?q=JTAI&sourceid=opera&num=0&ie=utf-8&oe=utf-8
  - "Jewish Teen Arts Institue"
 
 I now know it means - "Just Thinking About It"



http://www.acronymfinder.com is a decent source ITR.  (Except that it 
doesn't list the one I just used ... but hopefully it's understandable FTC.)

Stewart.

-- 
My e-mail is valid but not my primary mailbox.  Please keep replies on 
the 'group where everyone may benefit.
Jan 27 2005
parent reply "Regan Heath" <regan netwin.co.nz> writes:
On Thu, 27 Jan 2005 10:28:20 +0000, Stewart Gordon <smjg_1998 yahoo.com>  
wrote:

 Regan Heath wrote:

 On Wed, 26 Jan 2005 16:11:05 +0000, Stewart Gordon  
 <smjg_1998 yahoo.com>  wrote:


 JTAI



 initially :)
   
 http://www.google.com/search?q=JTAI&sourceid=opera&num=0&ie=utf-8&oe=utf-8
  - "Jewish Teen Arts Institue"
  I now know it means - "Just Thinking About It"



 http://www.acronymfinder.com is a decent source ITR.  (Except that it  
 doesn't list the one I just used ... but hopefully it's understandable  
 FTC.)



acronymfinder is where I got JTAI from... I cannot figure out ITR, but is  
FTC (From the context)?

Regan
Jan 27 2005
parent reply Norbert Nemec <Norbert Nemec-online.de> writes:
Regan Heath wrote:


 I cannot figure out ITR,



In This Respect
Jan 27 2005
parent Stewart Gordon <smjg_1998 yahoo.com> writes:
Norbert Nemec wrote:

 Regan Heath wrote:
 

 I cannot figure out ITR,



 In This Respect
 

 but is FTC (From the context)?






Got it in two.

Stewart.

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My e-mail is valid but not my primary mailbox.  Please keep replies on 
the 'group where everyone may benefit.
Jan 28 2005
prev sibling parent =?ISO-8859-1?Q?Anders_F_Bj=F6rklund?= <afb algonet.se> writes:
Pete wrote:


 I don't know much about parsing programming language. But I want to know what
 makes C++ hard to parse and does D these things right?



I have full sympathy for the parser and compiler,
as I can hardly parse regular C++ code myself :-)

--anders
Jan 26 2005