error on "--++ bla bla bla" - Haskell-Cafe - Haskell.org

newer
Journals on Haskell and FP?

error on "--++ bla bla bla"

older
combinatorial search with running...

Hong Yang

30 Sep 2009 30 Sep '09

7:52 p.m.

Hi, I got an error if one of lines reads "--++ bla bla bla" where I tried to comment, but "-- ++ bla bla bla" (notice the space after "--") is OK. Do you think this revealed a tiny bug in the GHC compiler (I am using Windows Haskell Platform 2009.2.0.2)? Thanks, Hong

Attachments:

attachment.html (text/html — 331 bytes)

Reply

Sign in to reply online Use email software

Show replies by date

Daniel Peebles

30 Sep 30 Sep

8:05 p.m.

I don't think it's a bug. --++ is a valid operator, whereas -- introduces a comment. In GHCI: Prelude> let (--++) = (+) in 5 --++ 6 11 Hope this helps, Dan On Wed, Sep 30, 2009 at 7:52 PM, Hong Yang wrote:

Hi,

I got an error if one of lines reads "--++ bla bla bla" where I tried to comment, but "-- ++ bla bla bla" (notice the space after "--") is OK.

Do you think this revealed a tiny bug in the GHC compiler (I am using Windows Haskell Platform 2009.2.0.2)?

Thanks,

Hong

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Reply

Sign in to reply online Use email software

Hong Yang

10:41 p.m.

But in my program, I did not define "--++". Also in GHCI, Prelude> :t (--++) No in scope: '--++' Prelude> :t (+) (+) :: (Num a) => a -> a -> a Thanks, Hong On Wed, Sep 30, 2009 at 7:05 PM, Daniel Peebles wrote:

I don't think it's a bug. --++ is a valid operator, whereas -- introduces a comment.

In GHCI:

Prelude> let (--++) = (+) in 5 --++ 6 11

Hope this helps, Dan

On Wed, Sep 30, 2009 at 7:52 PM, Hong Yang wrote:

...
Hi,

I got an error if one of lines reads "--++ bla bla bla" where I tried to comment, but "-- ++ bla bla bla" (notice the space after "--") is OK.

Do you think this revealed a tiny bug in the GHC compiler (I am using Windows Haskell Platform 2009.2.0.2)?

Thanks,

Hong

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Reply

Sign in to reply online Use email software

Ketil Malde

1 Oct 1 Oct

3:57 a.m.

Hong Yang writes:

But in my program, I did not define "--++".

And that's what the error tells you, no? Defining operators (or not) doesn't change the syntax. Since the lexeme --++ is syntactially a valid operator, it will be parsed as such, regardless of whether it is defined or not. -k -- If I haven't seen further, it is by standing in the footprints of giants

Reply

Sign in to reply online Use email software

Sebastian Sylvan

30 Sep 30 Sep

8:36 p.m.

On Thu, Oct 1, 2009 at 12:52 AM, Hong Yang wrote:

Hi,

I got an error if one of lines reads "--++ bla bla bla" where I tried to comment, but "-- ++ bla bla bla" (notice the space after "--") is OK.

Do you think this revealed a tiny bug in the GHC compiler (I am using Windows Haskell Platform 2009.2.0.2)?

Line comments start with "-- ", not just "--". -- Sebastian Sylvan

Reply

Sign in to reply online Use email software

Hong Yang

10:48 p.m.

Nowhere any Haskell book mentioned "line comments start with "-- ", not just "--"." It is just people usually put "-- " ahead of comments. I can successfully compile "--print bla bla bla." On Wed, Sep 30, 2009 at 7:36 PM, Sebastian Sylvan < sebastian.sylvan@gmail.com> wrote:

On Thu, Oct 1, 2009 at 12:52 AM, Hong Yang wrote:

...
Hi,

I got an error if one of lines reads "--++ bla bla bla" where I tried to comment, but "-- ++ bla bla bla" (notice the space after "--") is OK.

Do you think this revealed a tiny bug in the GHC compiler (I am using Windows Haskell Platform 2009.2.0.2)?

Line comments start with "-- ", not just "--".

-- Sebastian Sylvan

Reply

Sign in to reply online Use email software

Alexander Dunlap

10:56 p.m.

Comments are started with "--" followed by a character that is not a symbol character. If it is followed by a symbol character (e.g. "*") then the "--" plus the symbol (e.g. "--*") parses as an operator rather than a comment. "p" is not a symbol, so the "--" starts a comment. For a precise description of Haskell syntax, see the Haskell98 Report[1]. It's quite readable, at least in comparison to other "precise" documents I've attempted to read. Hope that helps. Alex On Wed, Sep 30, 2009 at 7:48 PM, Hong Yang wrote:

Nowhere any Haskell book mentioned "line comments start with "-- ", not just "--"." It is just people usually put "-- " ahead of comments.

I can successfully compile "--print bla bla bla." On Wed, Sep 30, 2009 at 7:36 PM, Sebastian Sylvan wrote:

...
On Thu, Oct 1, 2009 at 12:52 AM, Hong Yang wrote:

...
Hi,

I got an error if one of lines reads "--++ bla bla bla" where I tried to comment, but "-- ++ bla bla bla" (notice the space after "--") is OK.

Do you think this revealed a tiny bug in the GHC compiler (I am using Windows Haskell Platform 2009.2.0.2)?

Line comments start with "-- ", not just "--". -- Sebastian Sylvan

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Reply

Sign in to reply online Use email software

Alexander Dunlap

11:57 p.m.

Oops...forgot the footnote. The lexical syntax part of the report is at http://haskell.org/onlinereport/lexemes.html. Alex On Wed, Sep 30, 2009 at 7:56 PM, Alexander Dunlap wrote:

Comments are started with "--" followed by a character that is not a symbol character. If it is followed by a symbol character (e.g. "*") then the "--" plus the symbol (e.g. "--*") parses as an operator rather than a comment. "p" is not a symbol, so the "--" starts a comment.

For a precise description of Haskell syntax, see the Haskell98 Report[1]. It's quite readable, at least in comparison to other "precise" documents I've attempted to read.

Hope that helps.

Alex

On Wed, Sep 30, 2009 at 7:48 PM, Hong Yang wrote:

...
Nowhere any Haskell book mentioned "line comments start with "-- ", not just "--"." It is just people usually put "-- " ahead of comments.

I can successfully compile "--print bla bla bla." On Wed, Sep 30, 2009 at 7:36 PM, Sebastian Sylvan wrote:

...
On Thu, Oct 1, 2009 at 12:52 AM, Hong Yang wrote:

...
Hi,

I got an error if one of lines reads "--++ bla bla bla" where I tried to comment, but "-- ++ bla bla bla" (notice the space after "--") is OK.

Do you think this revealed a tiny bug in the GHC compiler (I am using Windows Haskell Platform 2009.2.0.2)?

Line comments start with "-- ", not just "--". -- Sebastian Sylvan

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Reply

Sign in to reply online Use email software

5715

Age (days ago)

5716

Last active (days ago)

Download

7 comments

5 participants

tags

participants (5)

Alexander Dunlap
Daniel Peebles
Hong Yang
Ketil Malde
Sebastian Sylvan