Re: Preliminary Haskell 1.3 report now available

1996-03-08 Thread Fergus Henderson


Thomas Hallgren [EMAIL PROTECTED] writes:

 In the syntax for labeled fields (records) the symbol - is chosen
 as the operator used to associate a label with a value in
 constructions and patterns:
[...]
 According to a committee member, there were no convincing reasons
 why - was chosen. Other symbols, like = and := were also considered.

I support Thomas Hallgen's suggestion that `=' be used instead.
Another reason, in addition to the two he mentioned, is that the `-'
symbol is very unintuitive when used for pattern matching, because the
arrow is in the *opposite* direction to the data-flow.  I find this
very confusing.

-- 
Fergus Henderson  | Designing grand concepts is fun;
[EMAIL PROTECTED]   | finding nitty little bugs is just work.
http://www.cs.mu.oz.au/~fjh   | -- Brooks, in "The Mythical Man-Month".
PGP key fingerprint: 00 D7 A2 27 65 09 B6 AC  8B 3E 0F 01 E7 5D C4 3F






Re: Preliminary Haskell 1.3 report now available

1996-03-07 Thread Lennart Augustsson



I always favoured `=' over `-', but I don't care much.

-- Lennart






Re: Preliminary Haskell 1.3 report now available

1996-03-07 Thread Thomas Hallgren


First, I am happy to see that Haskell 1.3, with its many valuable
improvements over Haskell 1.2, is finally getting ready,
but I also have a comment:

In the syntax for labeled fields (records) the symbol - is chosen
as the operator used to associate a label with a value in
constructions and patterns:

data Date = Date {day, month, year :: Int}

today = Date{day - 11, month - 10, year - 1995}

According to a committee member, there were no convincing reasons
why - was chosen. Other symbols, like = and := were also considered.


Here are some (in my opinion) good reasons for using = instead of - :

1. In ordinary declarations, :: is used to specify the type of a name
   and = is used to specify its value:

day, month, year :: Int
day = 11; month = 10; year = 1995

   so for consistency I think the same notations should be used
   inside record values:

data Date = Date {day, month, year :: Int}
date :: Date
date = Date {day = 11, month = 10, year = 1995}

2. The - symbol is used also in list comprehensions and the new
   monad syntax ('do'):

[ 2*x | x - [1..10] ]


do c - getChar; putChar c

   In these uses of - the name on the lhs does not have the same
   type as the expression on the rhs (above, x::Int, but [1..10]::[Int]
   and c::Char but getChar::IO Char). The value that the lhs name
   (or, indeed, pattern) is bound to is "extracted" from the value
   of the rhs expression. This is very different from what happens
   with field labels, so a difference in syntax is motivated.


Sadly, I suspect it would be difficult to convince the committee to
change their minds about this at this late stage, but I am sure it
would be even more difficult to change it for a later version of
Haskell...

Regards,

Thomas Hallgren






Re: Preliminary Haskell 1.3 report now available

1996-03-07 Thread Lennart Augustsson



I always favoured `=' over `-', but I don't care much.

-- Lennart






Re: Preliminary Haskell 1.3 report now available

1996-03-07 Thread alms



 Thomas Hallgren [EMAIL PROTECTED] writes:
 
  In the syntax for labeled fields (records) the symbol - is chosen
  as the operator used to associate a label with a value in
  constructions and patterns:
 [...]
  According to a committee member, there were no convincing reasons
  why - was chosen. Other symbols, like = and := were also considered.
 
 I support Thomas Hallgen's suggestion that `=' be used instead.
 Another reason, in addition to the two he mentioned, is that the `-'
 symbol is very unintuitive when used for pattern matching, because the
 arrow is in the *opposite* direction to the data-flow.  I find this
 very confusing.
 

Indeed, a couple of reasons I find convincing myself:
1 - SML uses '=' too, therefore it is one less problem for people
moving to/from SML/Haskell.
2 - The '-' notation always reminds me of list comprehensions,
e.g. at first sight if I see an expression like
R{v - [1..10]}
I could think v is an integer (taken from [1..10]) when it is actually a list.
the following expression is also confusing:
[R{v - [1..x]} | x - [1..10]]
(defines a list of records)
An expression using records on the rhs of the '|' should be even more interesting
(and useful for obfuscated Haskell competitions).
The same applies for records with fields defined with list comprehensions.

Andre.

Andre SantosDepartamento de Informatica
e-mail: [EMAIL PROTECTED] Universidade Federal de Pernambuco
http://www.di.ufpe.br/~alms CP 7851, CEP 50732-970, Recife PE Brazil






Preliminary Haskell 1.3 report now available

1996-03-06 Thread peterson-john



Announcing a preliminary version of the Haskell 1.3 report.

The Haskell 1.3 report is nearly complete.  All technical issues
appear to be resolved and the report is nearly ready.  The report
will be finalized April 19.  Any comments must be submitted by
April 15.  We do not anticipate making any serious technical changes
is the current version.

The report is being made available both on the web and as a .dvi file.

A summary of changes made in the Haskell 1.3 report can be found in

http://www.cs.yale.edu/HTML/YALE/CS/haskell/haskell13.html

This has pointers to the html version of the report.

The dvi file is available via anonymous ftp at
ftp://haskell.cs.yale.edu/pub/haskell/report/new-report.dvi.gz

Send comments or questions to [EMAIL PROTECTED]