--- title: Rewriting the Futhark type checker | daily.dev description: A deep dive into the evolution of Futhark's type checker, from a simple single-pass checker to a four-stage pipeline. The author explains why the original... canonical: https://daily.dev/posts/rewriting-the-futhark-type-checker-xhvkwalfe twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Rewriting the Futhark type checker | daily.dev og:description: A deep dive into the evolution of Futhark's type checker, from a simple single-pass checker to a four-stage pipeline. The author explains why the original... og:url: https://daily.dev/posts/rewriting-the-futhark-type-checker-xhvkwalfe og:image: https://api.daily.dev/og/posts/XhvkwAlfe.png og:image:alt: Rewriting the Futhark type checker og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Rewriting the Futhark type checker **[Lobsters](https://daily.dev/sources/lobsters)** · 12 min read · 0 upvotes · 0 comments ## Summary A deep dive into the evolution of Futhark's type checker, from a simple single-pass checker to a four-stage pipeline. The author explains why the original Algorithm W-based approach broke down as features like size types, uniqueness types, and AUTOMAP were added. The new design separates concerns into: name resolution, ground type inference (constraint-based, unsized), size inference, and in-place update validation. Key benefits include better error messages (each stage has full info from prior stages), easier debugging via explicit constraint sets, and reduced code duplication. The refactoring achieved a slight speedup (~4%) despite adding more passes, through targeted optimizations. The post also discusses the tradeoffs of multi-pass vs. single-pass type checking and hints at future work on bidirectional type checking for size inference. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Full flattening of nested data parallelism](https://daily.dev/posts/full-flattening-of-nested-data-parallelism-f2cwulaod) · Lobsters · 0 upvotes · 0 comments - [Futhark by Example](https://daily.dev/posts/futhark-by-example-vnchxphd7) · Hacker News · 0 upvotes · 0 comments - ["Five-Point Haskell": Total Depravity \(and Defensive Typing\)](https://daily.dev/posts/five-point-haskell-total-depravity-and-defensive-typing--xwwoyitrt) · Planet Haskell · 0 upvotes · 0 comments --- Tags: [#general-programming](https://daily.dev/tags/general-programming), [#compiler](https://daily.dev/tags/compiler) [View this post on daily.dev](https://daily.dev/posts/rewriting-the-futhark-type-checker-xhvkwalfe) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Rewriting the Futhark type checker","url":"https://daily.dev/posts/rewriting-the-futhark-type-checker-xhvkwalfe","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/rewriting-the-futhark-type-checker-xhvkwalfe"},"datePublished":"2026-07-23T07:53:00.906Z","dateModified":"2026-07-23T07:53:20.906Z","description":"A deep dive into the evolution of Futhark's type checker, from a simple single-pass checker to a four-stage pipeline. 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