{"id":605223,"date":"2019-08-23T03:00:08","date_gmt":"2019-08-23T10:00:08","guid":{"rendered":"https:\/\/www.microsoft.com\/en-us\/research\/?post_type=msr-research-item&#038;p=605223"},"modified":"2021-09-14T03:29:02","modified_gmt":"2021-09-14T10:29:02","slug":"type-inference-as-constraint-solving-how-ghcs-type-inference-engine-actually-works","status":"publish","type":"msr-research-item","link":"https:\/\/www.microsoft.com\/en-us\/research\/publication\/type-inference-as-constraint-solving-how-ghcs-type-inference-engine-actually-works\/","title":{"rendered":"Type inference as constraint solving: how GHC&#8217;s type inference engine actually works"},"content":{"rendered":"<p>The Haskell compiler GHC includes a type inference engine for a rather sophisticated type system.\u00a0 You might worry that a complicated type system leads to a very complicated type inference engine. \u00a0 You&#8217;d be right, but we have learned a lot about how to structure type inference so that the complexity does not get out of control.<\/p>\n<p>In this talk, given at <a class=\"msr-external-link glyph-append glyph-append-open-in-new-tab glyph-append-xsmall\" rel=\"noopener noreferrer\" target=\"_blank\" href=\"https:\/\/zfoh.ch\/zurihac2019\/\">Zurihac 2019<span class=\"sr-only\"> (opens in new tab)<\/span><\/a>, I explain how GHC&#8217;s type inference engine actually works <span style=\"float: none;background-color: #ffffff;color: #333333;cursor: text;font-family: Georgia,'Times New Roman','Bitstream Charter',Times,serif;font-size: 16px;font-style: normal;font-variant: normal;font-weight: 400;letter-spacing: normal;text-align: left;text-decoration: none;text-indent: 0px;text-transform: none\">by first <\/span><em>generating<\/em><span style=\"float: none;background-color: #ffffff;color: #333333;cursor: text;font-family: Georgia,'Times New Roman','Bitstream Charter',Times,serif;font-size: 16px;font-style: normal;font-variant: normal;font-weight: 400;letter-spacing: normal;text-align: left;text-decoration: none;text-indent: 0px;text-transform: none\"> constraints and then <\/span><em>solving<\/em><span style=\"float: none;background-color: #ffffff;color: #333333;cursor: text;font-family: Georgia,'Times New Roman','Bitstream Charter',Times,serif;font-size: 16px;font-style: normal;font-variant: normal;font-weight: 400;letter-spacing: normal;text-align: left;text-decoration: none;text-indent: 0px;text-transform: none\"> them.<\/span><\/p>\n<p>Here are<\/p>\n<ul>\n<li><a class=\"msr-external-link glyph-append glyph-append-open-in-new-tab glyph-append-xsmall\" rel=\"noopener noreferrer\" target=\"_blank\" href=\"https:\/\/www.youtube.com\/watch?v=x3evzO8O9e8\">Video of my talk at ZuriHac 2019<span class=\"sr-only\"> (opens in new tab)<\/span><\/a>, sadly missing the end part of the talk<\/li>\n<li><a class=\"msr-external-link glyph-append glyph-append-open-in-new-tab glyph-append-xsmall\" rel=\"noopener noreferrer\" target=\"_blank\" href=\"https:\/\/www.youtube.com\/watch?v=-TJGhGa04F8\">Video of the same talk at Lambdale 2019<span class=\"sr-only\"> (opens in new tab)<\/span><\/a> (in a pub!)<\/li>\n<li><a href=\"https:\/\/www.microsoft.com\/en-us\/research\/wp-content\/uploads\/2019\/08\/Type-inference-as-constraint-solving-Jun-19.pptx\">Slides from the talk<\/a><\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The Haskell compiler GHC includes a type inference engine for a rather sophisticated type system.\u00a0 You might worry that a complicated type system leads to a very complicated type inference engine. \u00a0 You&#8217;d be right, but we have learned a lot about how to structure type inference so that the complexity does not get out 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