gistfile1.txt

return redis.smembersAsync('langs')
.then(function(languages){
   // I need to call `articleExists('foo', language)` for each member of `languages`.
   // `articleExists` returns a promise; if it does, indeed, exist, then the promise resolves to
   //    the result I need (a name.)
   // if the article does *not* exist, then the promise returned by `articleExists` is rejected,
   //    and I need to move on to the next element of `languages`
}

Procedural

var article = Promise.reject(new Promise.RejectionError("not found")); 
languages.forEach(function(lang) { 
    article = article.error(function(e) { return articleExists('foo', lang); }); 
}); 
return article;

Functional

return languages.reduce(function(article, lang) { 
    return article.error(function(e) { return articleExists('foo', lang); }); 
}, Promise.reject(new Promise.RejectionError("not found")));