{"action":"created","comment":{"url":"https://api.github.com/repos/JuliaLang/julia/pulls/comments/52775444","id":52775444,"diff_hunk":"@@ -213,6 +213,37 @@ that the result is of type ``Float64`` by writing::\n \n     Float64[ 0.25*x[i-1] + 0.5*x[i] + 0.25*x[i+1] for i=2:length(x)-1 ]\n \n+.. _man-generator-expressions:\n+\n+Generator Expressions\n+---------------------\n+\n+Comprehensions can also be written without the enclosing square brackets, producing\n+an object known as a generator. This object can be iterated to produce values on\n+demand, instead of allocating an array and storing them in advance\n+(see :ref:`_man-interfaces-iteration`).\n+For example, the following expression sums a series without allocating memory::\n+\n+    julia> sum(1/n^2 for n=1:1000)\n+    1.6439345666815615\n+\n+When writing a generator expression with multiple dimensions, it needs to be\n+enclosed in parentheses to avoid ambiguity::\n+\n+    julia> collect(1/(i+j) for i=1:2, j=1:2)\n+    ERROR: function collect does not accept keyword arguments","path":"doc/manual/arrays.rst","position":22,"original_position":22,"commit_id":"b937ae73c5b29bea6a23f369bc32fafaeea40887","original_commit_id":"b937ae73c5b29bea6a23f369bc32fafaeea40887","user":{"login":"nalimilan","id":1120448,"avatar_url":"https://avatars.githubusercontent.com/u/1120448?v=3","gravatar_id":"","url":"https://api.github.com/users/nalimilan","html_url":"https://github.com/nalimilan","followers_url":"https://api.github.com/users/nalimilan/followers","following_url":"https://api.github.com/users/nalimilan/following{/other_user}","gists_url":"https://api.github.com/users/nalimilan/gists{/gist_id}","starred_url":"https://api.github.com/users/nalimilan/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/nalimilan/subscriptions","organizations_url":"https://api.github.com/users/nalimilan/orgs","repos_url":"https://api.github.com/users/nalimilan/repos","events_url":"https://api.github.com/users/nalimilan/events{/privacy}","received_events_url":"https://api.github.com/users/nalimilan/received_events","type":"User","site_admin":false},"body":"I think the presence of the `for` makes this quite unambigous in the programmer's mind. You wouldn't write a generator and then a keyword argument without adding parentheses around the former.\r\n\r\nIt's ambiguous for the parser, but as @StefanKarpinski noted `;` can be used to pass keyword arguments.","created_at":"2016-02-12T18:02:32Z","updated_at":"2016-02-12T18:02:32Z","html_url":"https://github.com/JuliaLang/julia/pull/14848#discussion_r52775444","pull_request_url":"https://api.github.com/repos/JuliaLang/julia/pulls/14848","_links":{"self":{"href":"https://api.github.com/repos/JuliaLang/julia/pulls/comments/52775444"},"html":{"href":"https://github.com/JuliaLang/julia/pull/14848#discussion_r52775444"},"pull_request":{"href":"https://api.github.com/repos/JuliaLang/julia/pulls/14848"}}},"pull_request":{"url":"https://api.github.com/repos/JuliaLang/julia/pulls/14848","id":57610361,"html_url":"https://github.com/JuliaLang/julia/pull/14848","diff_url":"https://github.com/JuliaLang/julia/pull/14848.diff","patch_url":"https://github.com/JuliaLang/julia/pull/14848.patch","issue_url":"https://api.github.com/repos/JuliaLang/julia/issues/14848","number":14848,"state":"open","locked":false,"title":"RFC: generator expressions","user":{"login":"JeffBezanson","id":744556,"avatar_url":"https://avatars.githubusercontent.com/u/744556?v=3","gravatar_id":"","url":"https://api.github.com/users/JeffBezanson","html_url":"https://github.com/JeffBezanson","followers_url":"https://api.github.com/users/JeffBezanson/followers","following_url":"https://api.github.com/users/JeffBezanson/following{/other_user}","gists_url":"https://api.github.com/users/JeffBezanson/gists{/gist_id}","starred_url":"https://api.github.com/users/JeffBezanson/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/JeffBezanson/subscriptions","organizations_url":"https://api.github.com/users/JeffBezanson/orgs","repos_url":"https://api.github.com/users/JeffBezanson/repos","events_url":"https://api.github.com/users/JeffBezanson/events{/privacy}","received_events_url":"https://api.github.com/users/JeffBezanson/received_events","type":"User","site_admin":false},"body":"I realized a good approach to comprehensions would be to add the generalized syntax (#4470) first, and once we are happy with how it works then use it to implement comprehensions.\r\n\r\nExample:\r\n\r\n```\r\njulia> sqrt(6sum(1/i^2 for i=1:1000000))\r\n3.1415916986605086\r\n```\r\n","created_at":"2016-01-29T06:16:33Z","updated_at":"2016-02-12T18:02:32Z","closed_at":null,"merged_at":null,"merge_commit_sha":"0a46dca5fe9a81bfff5ea5008dbb4bce2b2ebb4e","assignee":null,"milestone":null,"commits_url":"https://api.github.com/repos/JuliaLang/julia/pulls/14848/commits","review_comments_url":"https://api.github.com/repos/JuliaLang/julia/pulls/14848/comments","review_comment_url":"https://api.github.com/repos/JuliaLang/julia/pulls/comments{/number}","comments_url":"https://api.github.com/repos/JuliaLang/julia/issues/14848/comments","statuses_url":"https://api.github.com/repos/JuliaLang/julia/statuses/b937ae73c5b29bea6a23f369bc32fafaeea40887","head":{"label":"JuliaLang:jb/generators","ref":"jb/generators","sha":"b937ae73c5b29bea6a23f369bc32fafaeea40887","user":{"login":"JuliaLang","id":743164,"avatar_url":"https://avatars.githubusercontent.com/u/743164?v=3","gravatar_id":"","url":"https://api.github.com/users/JuliaLang","html_url":"https://github.com/JuliaLang","followers_url":"https://api.github.com/users/JuliaLang/followers","following_url":"https://api.github.com/users/JuliaLang/following{/other_user}","gists_url":"https://api.github.com/users/JuliaLang/gists{/gist_id}","starred_url":"https://api.github.com/users/JuliaLang/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/JuliaLang/subscriptions","organizations_url":"https://api.github.com/users/JuliaLang/orgs","repos_url":"https://api.github.com/users/JuliaLang/repos","events_url":"https://api.github.com/users/JuliaLang/events{/privacy}","received_events_url":"https://api.github.com/users/JuliaLang/received_events","type":"Organization","site_admin":false},"repo":{"id":1644196,"name":"julia","full_name":"JuliaLang/julia","owner":{"login":"JuliaLang","id":743164,"avatar_url":"https://avatars.githubusercontent.com/u/743164?v=3","gravatar_id":"","url":"https://api.github.com/users/JuliaLang","html_url":"https://github.com/JuliaLang","followers_url":"https://api.github.com/users/JuliaLang/followers","following_url":"https://api.github.com/users/JuliaLang/following{/other_user}","gists_url":"https://api.github.com/users/JuliaLang/gists{/gist_id}","starred_url":"https://api.github.com/users/JuliaLang/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/JuliaLang/subscriptions","organizations_url":"https://api.github.com/users/JuliaLang/orgs","repos_url":"https://api.github.com/users/JuliaLang/repos","events_url":"https://api.github.com/users/JuliaLang/events{/privacy}","received_events_url":"https://api.github.com/users/JuliaLang/received_events","type":"Organization","site_admin":false},"private":false,"html_url":"https://github.com/JuliaLang/julia","description":"The 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