Struct builders

Question

Struct builders

segeljakt opened this issue 5 years ago · comments

The docs say:

Any struct whose fields are builders can also be used as a builder. This is used to build multiple results at the same time.

But, when I compile:

|source: vec[i32]|
    let final = for(source, {appender[i32], appender[i32]}, |sink, index, element|
        merge(sink, {element, element})
    );
    {result(final.$0), result(final.$1)}

I get:

[info] 15:49:09.591: Started weld_module_compile
[info] 15:49:09.594: Started parsing program
[info] 15:49:09.608: Done parsing program
[info] 15:49:09.608: Started compiling program
[debug] 15:49:09.611: After macro substitution:
|source:vec[i32]|
  (let final:?=(for(
    source:?,
    {appender[i32],appender[i32]},
    |sink:?,index:?,element:?|
      merge(sink:?,{element:?,element:?})
  ));{result(
    final.$0
  ),result(
    final.$1
  )})

[info] 15:49:09.612: Done compiling program
REPL: Compile error: Internal error: Merge called on non-builder
>>>

My expectation was that you could merge structs which only contain builders, and also call result on structs which only contain builders.

Shoumik Palkar · Answer 1 · Fri Jul 19 2019 22:29:27 GMT+0800 (China Standard Time)

Try changing your merge to be {merge(sink.$0, element), merge(sink.$1, element)} (you need to explicitly specify the merge for each builder in the struct).

On Fri, Jul 19, 2019 at 6:50 AM segeljakt ***@***.***> wrote: The docs say: Any struct whose fields are builders can also be used as a builder. This is used to build multiple results at the same time. But, when I compile: |source: vec[i32]| let final = for(source, {appender[i32], appender[i32]}, |sink, index, element| merge(sink, {element, element}) ); {result(final.$0), result(final.$1)} I get: [info] 15:49:09.591: Started weld_module_compile [info] 15:49:09.594: Started parsing program [info] 15:49:09.608: Done parsing program [info] 15:49:09.608: Started compiling program [debug] 15:49:09.611: After macro substitution: |source:vec[i32]| (let final:?=(for( source:?, {appender[i32],appender[i32]}, |sink:?,index:?,element:?| merge(sink:?,{element:?,element:?}) ));{result( final.$0 ),result( final.$1 )}) [info] 15:49:09.612: Done compiling program REPL: Compile error: Internal error: Merge called on non-builder >>> My expectation was that you could merge structs which only contain builders, and also call result on structs which only contain builders. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#464?email_source=notifications&email_token=AAKMEY5UTCAG6ZFX3S6B5U3QAHBDJA5CNFSM4IFGFODKYY3PNVWWK3TUL52HS4DFUVEXG43VMWVGG33NNVSW45C7NFSM4HAIYPGA>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAKMEY7AVMZRA2UALOSFILDQAHBDJANCNFSM4IFGFODA> .

-- Shoumik

Klas Segeljakt · Answer 2 · Fri Jul 19 2019 23:09:44 GMT+0800 (China Standard Time)

Ok, thanks, makes sense :)

I have another question regarding builders. What happens internally in Weld when you swap the field positions of two builders? E.g:

|source: vec[i32]|
    let final = for(source, {appender[i32], appender[i32]}, |sink, index, element|
        {merge(sink.$1, 1), merge(sink.$0, 0)}
    );
    {result(final.$0), result(final.$1)}

Shoumik Palkar · Answer 3 · Fri Jul 19 2019 23:46:34 GMT+0800 (China Standard Time)

That's fine as long as you maintain their linearity property (i.e., each builder should be consumed *exactly* once per control path) and the types of the swapped builders are the same if you're inside a for loop. We don't have a compile time check for this at the moment unfortunately (it's in the works though!)

…

On Fri, Jul 19, 2019 at 8:09 AM segeljakt ***@***.***> wrote: Ok, thanks, makes sense :) I have another question regarding builders. What happens internally in Weld when you swap the field positions of two builders? E.g: |source: vec[i32]| let final = for(source, {appender[i32], appender[i32]}, |sink, index, element| {merge(sink.$1, 1), merge(sink.$0, 0)} ); {result(final.$0), result(final.$1)} — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#464?email_source=notifications&email_token=AAKMEY776IQO2UN2HVRVQHTQAHKLVA5CNFSM4IFGFODKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOD2L5DZQ#issuecomment-513266150>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAKMEY6NPDYUVNSAC2266NTQAHKLVANCNFSM4IFGFODA> .

-- Shoumik

Shoumik Palkar · Answer 4 · Fri Jul 19 2019 23:48:44 GMT+0800 (China Standard Time)

Sorry, realized you asked what happens internally: you can think of the builder as a C struct, so swapping them within a struct will effectively swap the struct values. On Fri, Jul 19, 2019 at 8:46 AM Shoumik Palkar <shoumikpalkar@gmail.com> wrote:

…

That's fine as long as you maintain their linearity property (i.e., each builder should be consumed *exactly* once per control path) and the types of the swapped builders are the same if you're inside a for loop. We don't have a compile time check for this at the moment unfortunately (it's in the works though!) On Fri, Jul 19, 2019 at 8:09 AM segeljakt ***@***.***> wrote: > Ok, thanks, makes sense :) > > I have another question regarding builders. What happens internally in > Weld when you swap the field positions of two builders? E.g: > > |source: vec[i32]| > let final = for(source, {appender[i32], appender[i32]}, |sink, index, element| > {merge(sink.$1, 1), merge(sink.$0, 0)} > ); > {result(final.$0), result(final.$1)} > > — > You are receiving this because you commented. > Reply to this email directly, view it on GitHub > <#464?email_source=notifications&email_token=AAKMEY776IQO2UN2HVRVQHTQAHKLVA5CNFSM4IFGFODKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOD2L5DZQ#issuecomment-513266150>, > or mute the thread > <https://github.com/notifications/unsubscribe-auth/AAKMEY6NPDYUVNSAC2266NTQAHKLVANCNFSM4IFGFODA> > . > -- Shoumik

-- Shoumik