Ast_uncurry_gen (melange.Melange_ppx_lib.Ast_uncurry

let to_uncurry_fn: 
  Melange_compiler_libs.Location.t =>
  Melange_compiler_libs.Ast_mapper.mapper =>
  Asttypes.arg_label =>
  Melange_compiler_libs.Parsetree.pattern =>
  Melange_compiler_libs.Parsetree.expression =>
  Melange_compiler_libs.Parsetree.expression_desc;

function can only take one argument, that is the reason we did not adopt it syntax:

fun [@bs] pat pat1-> body

to_uncurry_fn (fun pat -> (fun pat1 -> ... body))

let to_method_callback: 
  Melange_compiler_libs.Location.t =>
  Melange_compiler_libs.Ast_mapper.mapper =>
  Asttypes.arg_label =>
  Melange_compiler_libs.Parsetree.pattern =>
  Melange_compiler_libs.Parsetree.expression =>
  Melange_compiler_libs.Parsetree.expression_desc;

syntax:

fun [@bs.this] obj pat pat1 -> body