sweet.js: transforming occurrences of a repeated token -

i want define sweet macro transforms

{ a, b } # o 

into

{ o.a, o.b } 

my current attempt is

macro (#) {     case infix { { $prop:ident (,) ... } | _ $o } => {     return #{ { $prop: $o.$prop (,) ... } }   } } 

however, give me

syntaxerror: [patterns] ellipses level not match in template 

i suspect don't understand how ... works, , may need somehow loop on values of $prop , build syntax objects each , somehow concatenate them, i'm @ loss how that.

the problem syntax expander thinks you're trying expand $o.$prop instead of $prop: $o.$prop. here's solution:

macro (#) {     rule infix { { $prop:ident (,) ... } | $o:ident } => {     { $($prop: $o.$prop) (,) ... }   } } 

notice placed unit of code in $() block of own disambiguate ellipse expansion.

example: var x = { a, b } # o; becomes var x = { a: o.a, b: o.b };.