[svn:perl6-synopsis] r11975 - doc/trunk/design/syn

[la...@cvs.perl.org]

Author: larry
Date: Tue Sep 12 21:09:33 2006
New Revision: 11975

Modified:
doc/trunk/design/syn/S03.pod

Log:
tweaks to crossop syntax

Modified: doc/trunk/design/syn/S03.pod
==============================================================================
--- doc/trunk/design/syn/S03.pod (original)
+++ doc/trunk/design/syn/S03.pod Tue Sep 12 21:09:33 2006
@@ -1031,14 +1031,22 @@

=head1 Cross operators

-The final metaoperator is the C<X> metaoperator. It applies the
+The final metaoperator is the cross metaoperator. It is formed syntactically
+by placing an infix operator between two C<X> characters. It applies the
modified operator across all permutations of its list arguments. All
-C<X> operators are of list infix precedence, and are list associative.
+cross operators are of list infix precedence, and are list associative.

-The bare form of C<X> is considered an operator in its own right.
-Saying:
+The string concatenating form is:
+
+ <a b> X~X <1 2> # 'a1', 'a2', 'b1', 'b2'
+
+The C<X~X> operator desugars to something like:
+
+ [~]«( <a b> X <1 2> ) # 'a1', 'a2', 'b1', 'b2'

- <a b> X 1,2 X <x y>
+The list concatenating form
+
+ <a b> X,X 1,2 X,X <x y>

produces

@@ -1051,33 +1059,25 @@
['b', 2, 'x'],
['b', 2, 'y']

-The string concatenating form is:
-
- <a b> X~ <1 2> # 'a1', 'a2', 'b1', 'b2'
-
-As a metaoperator, C<X~> operator desugars to something like:
-
- [~]«( <a b> X <1 2> ) # 'a1', 'a2', 'b1', 'b2'
+The string and list forms are common enough to have shortcuts, C<X>
+and C<XX> respectively. See below.

-Any existing, non-mutating infix operator may be used after the C<X>.
+For the general form, any existing, non-mutating infix operator
+may be used.

- 1,2 X* 3,4 # 3,4,6,8
+ 1,2 X*X 3,4 # 3,4,6,8

(Note that C<< <== >> and C<< ==> >> are considered mutating, as well as
all assignment operators.)

If the underlying operator is non-associating, so is the metaoperator:

- @a Xcmp @b Xcmp @c # ILLEGAL
- @a Xeq @b Xeq @c # ok
+ @a XcmpX @b XcmpX @c # ILLEGAL
+ @a XeqX @b XeqX @c # ok

In fact, though the C<X> operators are all list associative
syntactically, the underlying operator is always applied with its
-own associativity.
-
-Unlike bare C<X>, the C<X,> form flattens much like C<[,]> does.
-
- <a b> X, <1 2> # 'a', '1', 'a', '2', 'b', '1', 'b', '2'
+own associativity, just as the corresponding reduce operator would do.

Note that only the first term of an C<X> operator may reasonably be
an infinite list.
@@ -1460,16 +1460,24 @@

=head1 Crossing arrays

-In contrast to the zip operator, the C<X> operator returns all the
+In contrast to the zip operator, the C<XX> operator returns all the
permutations of its sublists. Hence you may say:

- <a b> X <1 2>
+ <a b> XX <1 2>

and you end up with

['a', '1'], ['a', '2'], ['b', '1'], ['b', '2']

-It is really a variant of the C<X> metaoperator mentioned earlier.
+The C<X> variant crosses the arrays but concatenates strings:
+
+ <a b> X <1 2>
+
+produces
+
+ 'a1', 'a2', 'b1', 'b2'
+
+The resemblance to C<x> and C<xx> is not entirely accidental.

=head1 Minimal whitespace DWIMmery

@@ -1551,7 +1559,7 @@
!!! ... ???
[+] [*] [<] [,] [\+] [\*] etc.
(also = as list assignment)
- list infix ¥ <== ==> X X~ X* Xeqv etc.
+ list infix ¥ <== ==> X XX X~X X*X XeqvX etc.
loose and and
loose or or xor err
expr terminator ; {} as control block, statement modifiers

[cma...@gmail.com]

svn log, speaking on larry's behalf (>):

> +The string concatenating form is:
> +
> + <a b> X~X <1 2> # 'a1', 'a2', 'b1', 'b2'
> +
> +The C<X~X> operator desugars to something like:
> +
> + [~]«( <a b> X <1 2> ) # 'a1', 'a2', 'b1', 'b2'

...and later...

> +The C<X> variant crosses the arrays but concatenates strings:
> +
> + <a b> X <1 2>
> +
> +produces
> +
> + 'a1', 'a2', 'b1', 'b2'

If the C<X> variant already concatenates strings, why is it done
explicitly in the desugaring of C<X~X>? Probably not what you
intended.

Kindly,
// masak

[Daniel Hulme]

> svn log, speaking on larry's behalf (>):
> > +The string concatenating form is:
> > +
> > + <a b> X~X <1 2> # 'a1', 'a2', 'b1', 'b2'
> > +
> > +The C<X~X> operator desugars to something like:
> > +
> > + [~]«( <a b> X <1 2> ) # 'a1', 'a2', 'b1', 'b2'

^

> If the C<X> variant already concatenates strings, why is it done
> explicitly in the desugaring of C<X~X>? Probably not what you
> intended.

I think it's just that the change is incomplete. It looks like the X
I've marked should have been changed to a XX.

--
"Of all things, good sense is the most fairly distributed: everyone
thinks he is so well supplied with it that even those who are the
hardest to satisfy in every other respect never desire more of it than
they already have." -- Descartes, 1637 http://surreal.istic.org/

[cma...@gmail.com]

Daniel (>), Carl (>>), svn log, speaking on larry's behalf (>>>):

> > > +The string concatenating form is:
> > > +
> > > + <a b> X~X <1 2> # 'a1', 'a2', 'b1', 'b2'
> > > +
> > > +The C<X~X> operator desugars to something like:
> > > +
> > > + [~]�( <a b> X <1 2> ) # 'a1', 'a2', 'b1', 'b2'
> ^
>
> > If the C<X> variant already concatenates strings, why is it done
> > explicitly in the desugaring of C<X~X>? Probably not what you
> > intended.
>
> I think it's just that the change is incomplete. It looks like the X
> I've marked should have been changed to a XX.

Yes, I suspected so too, though I wasn't sure so I didn't write it. :)

Even better, it could be changed into C<X,X>, unnecessitating another
desugaring (mental or parse-al).

// Carl