hphp/hack/test/typecheck/reduce_lambda.php

   1 <?hh // strict
   2 // Copyright 2004-present Facebook. All Rights Reserved.
   3
   4 function reduce<Tv, Ta>(
   5   Traversable<Tv> $traversable,
   6   (function(Ta, Tv): Ta) $accumulator,
   7   Ta $initial,
   8 ): Ta {
   9   return $initial;
  10 }
  11 function testit(varray<shape('page_id' => string, 'page_name' => string)> $v):void {
  12   // So: Tv appears in a covariant position in a lambda parameter type
  13   // Ta appears in a covariant position in the result
  14   // And we have varray<shape(...) <: Traversable<Tv>
  15   // So shape(...) <: Tv
  16   // Also vec<nothing> <: Ta
  17   // But
  18   $pages_document = reduce<_,_>($v, ($pages_document, $res) ==> {
  19       //hh_show_env();
  20       $pages_document[] = Map {
  21         "uid" => (string)$res['page_id'],
  22         "text" => $res['page_name'],
  23       };
  24       //hh_show_env();
  25       return $pages_document;
  26     }, vec[]);
  27 }