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Allow Nil to represent holes in sparse arrays
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This commit affects the way arrays are rendered with .raku, and it
affects the way Nil is interpreted as a value when initializing an
array.

This is achieved by the following conceptual changes:

1. in .raku, output a hole (nqp::isnull) as `Nil`

To achieve this, several Iterator classes have their private method
`!hole` turned into a outside visible method `hole` with the
"is implementation-detail" trait.  This allows Array.raku to override
the handling of a hole by mixing in a "hole" method into the iterator
that produces "Nil".

2. in STORE and circumfix:<[ ]> (and its helpers), interprete Nil as
   *skipping* an element to be initialized.  If there was only one
   element specified, and it was Nil, then return an empty Array.

3. fix some Rakudo::Internals helper methods to recognize nqp::null
   values without throwing a tantrum.

This breaks a few tests in roast, that expect that [Nil] will return
[Any], where now it will return [Nil].  There is no further test breakage.

This does *not* fix the case of Nil in arrays constrained with a type
smiley.  Generating the .raku of these is fine, but it won't roundtrip
because `my Int:D @A = 1,Nil,3` is a runtime error.  FWIW, I think this
is actually incorrect behaviour, or at least unproductive behaviour.

This work was done in reply to

  Raku/problem-solving#279

One of the proposed solutions was to introduce a Hole class with special
semantics.  Should that proposal be accepted, then it is mostly replacing
`Nil` by `Hole` in most of this commit.
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@lizmat
lizmat committed Jun 15, 2021
1 parent 168da39 commit 484baa6
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Showing 4 changed files with 97 additions and 48 deletions.
79 changes: 58 additions & 21 deletions src/core.c/Array.pm6
View file
Expand Up @@ -20,14 +20,26 @@ my class Array { # declared in BOOTSTRAP
}

method push(Mu \value --> Nil) {
nqp::push($!target, nqp::p6scalarwithvalue($!descriptor, value));
my \cont := nqp::p6scalarwithvalue($!descriptor,value); # typecheck
nqp::eqaddr(value,Nil)
?? nqp::setelems($!target,nqp::add_i(nqp::elems($!target),1))
!! nqp::push($!target,cont)
}

method append(IterationBuffer:D \buffer --> Nil) {
nqp::while(
nqp::elems(buffer),
nqp::push($!target,
nqp::p6scalarwithvalue($!descriptor,nqp::shift(buffer))
nqp::stmts(
# make sure we typecheck any value being stored
(my \cont := nqp::p6scalarwithvalue(
$!descriptor,
(my \value := nqp::shift(buffer))
)),
nqp::if(
nqp::eqaddr(value,Nil),
nqp::setelems($!target,nqp::add_i(nqp::elems($!target),1)),
nqp::push($!target,cont)
)
)
);
}
Expand Down Expand Up @@ -106,7 +118,7 @@ my class Array { # declared in BOOTSTRAP
nqp::atpos($!reified,$!i = nqp::add_i($!i,1)),
nqp::if(
nqp::islt_i($!i,nqp::elems($!reified)),
self!hole($!i),
self.hole($!i),
nqp::if(
nqp::isconcrete($!todo),
nqp::if(
Expand All @@ -122,7 +134,7 @@ my class Array { # declared in BOOTSTRAP
)
)
}
method !hole(int $i) is raw {
method hole(int $i) is raw is implementation-detail {
nqp::p6scalarfromcertaindesc(
ContainerDescriptor::BindArrayPos.new($!descriptor,$!reified,$i)
)
Expand Down Expand Up @@ -160,7 +172,7 @@ my class Array { # declared in BOOTSTRAP
nqp::while( # doesn't sink
nqp::islt_i($i = nqp::add_i($i,1),$elems),
target.push(
nqp::ifnull(nqp::atpos($!reified,$i),self!hole($i))
nqp::ifnull(nqp::atpos($!reified,$i),self.hole($i))
)
),
($!i = $i),
Expand Down Expand Up @@ -213,11 +225,14 @@ my class Array { # declared in BOOTSTRAP
my \reified := nqp::create(IterationBuffer);
nqp::while(
nqp::islt_i(($i = nqp::add_i($i,1)),$elems),
nqp::bindpos(
reified, $i,
nqp::p6scalarwithvalue(
(BEGIN nqp::getcurhllsym('default_cont_spec')),
nqp::decont(nqp::atpos(params,$i))
nqp::unless(
nqp::isnull(my \value := nqp::decont(nqp::atpos(params,$i)))
|| nqp::eqaddr(value,Nil),
nqp::bindpos(reified,$i,
nqp::p6scalarwithvalue(
(BEGIN nqp::getcurhllsym('default_cont_spec')),
value
)
)
)
);
Expand Down Expand Up @@ -308,10 +323,10 @@ my class Array { # declared in BOOTSTRAP
nqp::p6bindattrinvres(self,List,'$!reified',buffer)
}
multi method STORE(Array:D: Mu \item --> Array:D) {
nqp::push(
(my \buffer = nqp::create(IterationBuffer)),
nqp::p6scalarwithvalue($!descriptor, item)
);
my \buffer = nqp::create(IterationBuffer);
# Make sure we typecheck always
my \cont := nqp::p6scalarwithvalue($!descriptor,item);
nqp::push(buffer,cont) unless nqp::eqaddr(nqp::decont(item),Nil);
nqp::bindattr(self,List,'$!todo',Mu);
nqp::p6bindattrinvres(self,List,'$!reified',buffer)
}
Expand All @@ -324,7 +339,7 @@ my class Array { # declared in BOOTSTRAP

multi method Slip(Array:D: --> Slip:D) {

# A Slip-With-Descripto is a special kind of Slip that also has a
# A Slip-With-Descriptor is a special kind of Slip that also has a
# descriptor to be able to generate containers for null elements that
# have type and default information.
my class Slip-With-Descriptor is Slip {
Expand Down Expand Up @@ -1280,13 +1295,35 @@ my class Array { # declared in BOOTSTRAP
method dynamic() {
nqp::isnull($!descriptor) ?? False !! so $!descriptor.dynamic
}

multi method raku(Array:D \SELF: --> Str:D) {
my role NilHole { method hole(int $ --> Nil) { } }

SELF.rakuseen('Array', {
'$' x nqp::iscont(SELF) # self is always deconted
~ '['
~ self.map({nqp::decont($_).raku}).join(', ')
~ ',' x (self.elems == 1 && nqp::istype(self.AT-POS(0),Iterable))
~ ']'
my $iterator := SELF.iterator but NilHole;

my $parts := nqp::list_s;
nqp::push_s($parts,'$') if nqp::iscont(SELF);
nqp::push_s($parts,'[');
nqp::until(
nqp::eqaddr(
(my \value := nqp::decont($iterator.pull-one)),
IterationEnd
),
nqp::stmts(
nqp::push_s(
$parts,
nqp::if(nqp::isnull(value),'Nil',value.raku)
),
nqp::push_s($parts,', ')
)
);
nqp::pop_s($parts) unless nqp::isle_i(nqp::elems($parts),2);
nqp::push_s($parts,',')
if self.elems == 1 && nqp::istype(self.AT-POS(0),Iterable);
nqp::push_s($parts,']');

nqp::join('',$parts)
})
}
multi method WHICH(Array:D: --> ObjAt:D) { self.Mu::WHICH }
Expand Down
18 changes: 13 additions & 5 deletions src/core.c/Rakudo/Internals.pm6
View file
Expand Up @@ -706,11 +706,19 @@ my class Rakudo::Internals {

method MAYBE-STRING(Mu \thing, Str:D :$method = 'gist' --> Str:D) {
my Mu \decont = nqp::decont(thing);
nqp::can(decont, nqp::decont_s($method))
?? decont."$method"()
!! nqp::can(decont.HOW, 'name')
?? decont.^name
!! '?'
nqp::if(
nqp::isnull(decont),
'Nil',
nqp::if(
nqp::can(decont,nqp::decont_s($method)),
decont."$method"(),
nqp::if(
nqp::can(decont.HOW,'name'),
decont.^name,
'?'
)
)
)
}
method SHORT-STRING(Mu \thing, Str:D :$method = 'gist' --> Str:D) {
my str $str = nqp::unbox_s(self.MAYBE-STRING: thing, :$method);
Expand Down
20 changes: 10 additions & 10 deletions src/core.c/Rakudo/Iterator.pm6
View file
Expand Up @@ -3310,7 +3310,7 @@ class Rakudo::Iterator {
}
method new(\arr, Mu \des) { nqp::create(self)!SET-SELF(arr, des) }

method !hole(int $i) is raw {
method hole(int $i) is raw is implementation-detail {
nqp::p6scalarfromdesc(ContainerDescriptor::BindArrayPos.new(
$!descriptor, $!reified, $i))
}
Expand All @@ -3319,7 +3319,7 @@ class Rakudo::Iterator {
nqp::atpos($!reified,$!i = nqp::add_i($!i,1)),
nqp::if(
nqp::islt_i($!i,nqp::elems($!reified)), # found a hole
self!hole($!i),
self.hole($!i),
IterationEnd
)
)
Expand All @@ -3333,7 +3333,7 @@ class Rakudo::Iterator {
($todo = nqp::sub_i($todo,1))
&& nqp::islt_i(($i = nqp::add_i($i,1)),$elems),
target.push(
nqp::ifnull(nqp::atpos($!reified,$i),self!hole($i))
nqp::ifnull(nqp::atpos($!reified,$i),self.hole($i))
)
);

Expand All @@ -3349,7 +3349,7 @@ class Rakudo::Iterator {
nqp::while( # doesn't sink
nqp::islt_i($i = nqp::add_i($i,1),$elems),
target.push(
nqp::ifnull(nqp::atpos($!reified,$i),self!hole($i))
nqp::ifnull(nqp::atpos($!reified,$i),self.hole($i))
)
);
$!i = $i;
Expand Down Expand Up @@ -3485,7 +3485,7 @@ class Rakudo::Iterator {
}
method new(\list, Mu \des) { nqp::create(self)!SET-SELF(list, des) }

method !hole(int $i) is raw {
method hole(int $i) is raw is implementation-detail {
nqp::isnull($!descriptor)
?? Nil
!! nqp::p6scalarfromdesc(
Expand All @@ -3497,15 +3497,15 @@ class Rakudo::Iterator {

method pull-one() is raw {
nqp::isge_i(($!i = nqp::sub_i($!i,1)),0)
?? nqp::ifnull(nqp::atpos($!reified,$!i),self!hole($!i))
?? nqp::ifnull(nqp::atpos($!reified,$!i),self.hole($!i))
!! IterationEnd
}
method push-all(\target --> IterationEnd) {
my $reified := $!reified; # lexicals are faster than attributes
my int $i = $!i;
nqp::while( # doesn't sink
nqp::isge_i(($i = nqp::sub_i($i,1)),0),
target.push(nqp::ifnull(nqp::atpos($reified,$i),self!hole($i)))
target.push(nqp::ifnull(nqp::atpos($reified,$i),self.hole($i)))
);
$!i = $i;
}
Expand Down Expand Up @@ -3551,7 +3551,7 @@ class Rakudo::Iterator {
nqp::create(self)!SET-SELF(rotate, list, des)
}

method !hole(int $i) is raw {
method hole(int $i) is raw is implementation-detail {
nqp::isnull($!descriptor)
?? Nil
!! nqp::p6scalarfromdesc(
Expand All @@ -3568,7 +3568,7 @@ class Rakudo::Iterator {
$!reified,
($!i = nqp::mod_i(nqp::add_i($!i,1),nqp::elems($!reified)))
),
self!hole($!i)
self.hole($!i)
)
!! IterationEnd
}
Expand All @@ -3586,7 +3586,7 @@ class Rakudo::Iterator {
$reified,
($i = nqp::mod_i(nqp::add_i($i,1),$elems))
),
self!hole($i)
self.hole($i)
)
)
);
Expand Down
28 changes: 16 additions & 12 deletions src/core.c/array_operators.pm6
View file
Expand Up @@ -27,18 +27,22 @@ multi sub circumfix:<[ ]>(Iterable:D \iterable) {
)
}
multi sub circumfix:<[ ]>(Mu \x) { # really only for [$foo]
nqp::p6bindattrinvres(
nqp::create(Array),List,'$!reified',
nqp::stmts(
nqp::bindpos(
(my \reified := nqp::create(IterationBuffer)),
0,
nqp::p6scalarwithvalue(
(BEGIN nqp::getcurhllsym('default_cont_spec')),
nqp::decont(x)
)
),
reified
nqp::if(
nqp::eqaddr(nqp::decont(x),Nil),
Array.new,
nqp::p6bindattrinvres(
nqp::create(Array),List,'$!reified',
nqp::stmts(
nqp::bindpos(
(my \reified := nqp::create(IterationBuffer)),
0,
nqp::p6scalarwithvalue(
(BEGIN nqp::getcurhllsym('default_cont_spec')),
nqp::decont(x)
)
),
reified
)
)
)
}
Expand Down

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