[Caml-list] Unary negation parsing

[Caml-list] Unary negation parsing

[Stanislav Artemkin]

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Hi all,

I've just stumbled upon yet another question about unary negation parsing (
http://stackoverflow.com/questions/34044873/passing-negative-integer-to-a-function-in-ocaml
):

let f x = x + 1 in
f -1

is not valid in OCaml.

I'm just wondering why this issue is still not addressed in the parser? For
example, F# parses "f -1" as unary negation, but "f - 1" and "f-1" as
binary operator. It looks a bit tricky (as whitespace is taken into
account), but feels so natural when writing code.

Is there any reason we can't have the same in OCaml?

PS. I understand that it may break existing code, but it should be solvable
by a compiler option similar to -safe-string etc.

Thank you

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Re: [Caml-list] Unary negation parsing

[Gerd Stolpmann]

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Thinking that this is a mostly aesthetic question, with one little
exception:

# max_int;;
- : int = 4611686018427387903
# -4611686018427387904;;
- : int = -4611686018427387904
# 4611686018427387904;;    
- : int = -4611686018427387904
# 4611686018427387905;;
Error: Integer literal exceeds the range of representable integers of
type int

In short, the literal maxint+1 is accepted because minint=-(maxint+1),
and we don't have negative literals.

However, the question is whether it is worth the trouble changing it. As
you mention -safe-string, I just went through a large library and
updated it, and it was far from trivial (needed GADTs) and a lot of work
(something like 30 hours, really). I'm still skeptical whether changes
of this kind get you a real benefit.

Gerd


Am Mittwoch, den 02.12.2015, 22:59 +0400 schrieb Stanislav Artemkin:
> Hi all,
> 
> 
> I've just stumbled upon yet another question about unary negation
> parsing
> (http://stackoverflow.com/questions/34044873/passing-negative-integer-to-a-function-in-ocaml):
> 
> 
> let f x = x + 1 in
> f -1
> 
> 
> is not valid in OCaml.
> 
> 
> I'm just wondering why this issue is still not addressed in the
> parser? For example, F# parses "f -1" as unary negation, but "f - 1"
> and "f-1" as binary operator. It looks a bit tricky (as whitespace is
> taken into account), but feels so natural when writing code.
> 
> 
> Is there any reason we can't have the same in OCaml?
> 
> 
> PS. I understand that it may break existing code, but it should be
> solvable by a compiler option similar to -safe-string etc.
> 
> 
> Thank you
> 
> 

-- 
------------------------------------------------------------
Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
My OCaml site:          http://www.camlcity.org
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
------------------------------------------------------------

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Re: [Caml-list] Unary negation parsing

[Stanislav Artemkin]

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> In short, the literal maxint+1 is accepted because minint=-(maxint+1),
> and we don't have negative literals.

It looks strange that 4611686018427387904 is accepted (defect?), and OCaml
actually defines negative numeric literals according to
http://caml.inria.fr/pub/docs/manual-ocaml/lex.html

On the contrary, F# doesn't have negative numeric literals, but defines a
post-filtering of adjacent prefix tokens in 3.8.1. See
http://fsharp.org/specs/language-spec/3.0/FSharpSpec-3.0-final.pdf#page=28

Thanks

On Thu, Dec 3, 2015 at 12:49 AM, Gerd Stolpmann <info@gerd-stolpmann.de>
wrote:

> Thinking that this is a mostly aesthetic question, with one little
> exception:
>
> # max_int;;
> - : int = 4611686018427387903
> # -4611686018427387904;;
> - : int = -4611686018427387904
> # 4611686018427387904;;
> - : int = -4611686018427387904
> # 4611686018427387905;;
> Error: Integer literal exceeds the range of representable integers of
> type int
>
> In short, the literal maxint+1 is accepted because minint=-(maxint+1),
> and we don't have negative literals.
>
> However, the question is whether it is worth the trouble changing it. As
> you mention -safe-string, I just went through a large library and
> updated it, and it was far from trivial (needed GADTs) and a lot of work
> (something like 30 hours, really). I'm still skeptical whether changes
> of this kind get you a real benefit.
>
> Gerd
>
>
> Am Mittwoch, den 02.12.2015, 22:59 +0400 schrieb Stanislav Artemkin:
> > Hi all,
> >
> >
> > I've just stumbled upon yet another question about unary negation
> > parsing
> > (
> http://stackoverflow.com/questions/34044873/passing-negative-integer-to-a-function-in-ocaml
> ):
> >
> >
> > let f x = x + 1 in
> > f -1
> >
> >
> > is not valid in OCaml.
> >
> >
> > I'm just wondering why this issue is still not addressed in the
> > parser? For example, F# parses "f -1" as unary negation, but "f - 1"
> > and "f-1" as binary operator. It looks a bit tricky (as whitespace is
> > taken into account), but feels so natural when writing code.
> >
> >
> > Is there any reason we can't have the same in OCaml?
> >
> >
> > PS. I understand that it may break existing code, but it should be
> > solvable by a compiler option similar to -safe-string etc.
> >
> >
> > Thank you
> >
> >
>
> --
> ------------------------------------------------------------
> Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
> My OCaml site:          http://www.camlcity.org
> Contact details:        http://www.camlcity.org/contact.html
> Company homepage:       http://www.gerd-stolpmann.de
> ------------------------------------------------------------
>

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Re: [Caml-list] Unary negation parsing

[Mr. Herr]

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On 02.12.2015 19:59, Stanislav Artemkin wrote:
> Hi all,
>
> I've just stumbled upon yet another question about unary negation parsing
> (http://stackoverflow.com/questions/34044873/passing-negative-integer-to-a-function-in-ocaml):
>
> let f x = x + 1 in
> f -1
>
> is not valid in OCaml.
>
> I'm just wondering why this issue is still not addressed in the parser? For
> example, F# parses "f -1" as unary negation, but "f - 1" and "f-1" as binary
> operator. It looks a bit tricky (as whitespace is taken into account), but feels so
> natural when writing code.
>
> Is there any reason we can't have the same in OCaml?
>
> PS. I understand that it may break existing code, but it should be solvable by a
> compiler option similar to -safe-string etc.
>
I think this is a non-issue, and it is easily explained to every beginner. And you
say yourself: ... tricky .. whitespace ... may break existing code ...

/Str.



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