--- title: Tail-Call Interpreters in Rust | daily.dev description: A deep dive into implementing four VM dispatch strategies in Rust using the unstable `explicit_tail_calls` feature (`become` keyword): switch dispatch,... canonical: https://daily.dev/posts/tail-call-interpreters-in-rust-botv3otev twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Tail-Call Interpreters in Rust | daily.dev og:description: A deep dive into implementing four VM dispatch strategies in Rust using the unstable `explicit_tail_calls` feature (`become` keyword): switch dispatch,... og:url: https://daily.dev/posts/tail-call-interpreters-in-rust-botv3otev og:image: https://api.daily.dev/og/posts/BOtv3oteV.png og:image:alt: Tail-Call Interpreters in Rust 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. # Tail-Call Interpreters in Rust **[Hacker News](https://daily.dev/sources/hn)** · 19 min read · 0 upvotes · 0 comments ## Summary A deep dive into implementing four VM dispatch strategies in Rust using the unstable `explicit_tail_calls` feature (`become` keyword): switch dispatch, subroutine threading, indirect threading, and direct dispatch. The author benchmarks all four on a simple stack machine and a 16-bit register machine, finding direct dispatch the fastest (24.59 ns vs 79.93 ns for subroutine on the stack machine). Code examples show how each technique maps to Rust idioms, including use of `dyn Fn()` traits and static handler arrays, with discussion of control flow benefits like trap handling and exception-like patterns. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What does Rust's unstable explicit_tail_calls feature and the become keyword do for writing interpreters? The explicit_tail_calls feature lets a function guarantee that a recursive call is compiled as a jump instead of allocating a new stack frame, using the `become` keyword in place of a normal call or return. This makes deeply recursive interpreter dispatch loops safe from stack overflow, since each dispatch call reuses the current frame rather than growing the call stack. _Developers experimenting with unstable Rust features can track compiler changes like this one through daily.dev._ ### Which bytecode dispatch technique is fastest for a Rust interpreter: switch, subroutine threading, indirect threading, or direct dispatch? Direct dispatch, where each instruction handler tail-calls the next handler directly without a central dispatch function, performed best in both a simple stack machine (24.59 ns/iter) and a 16-bit register machine (62.87 ns/iter) benchmark. Switch dispatch and indirect threading trailed behind, while subroutine threading using dynamic Fn() trait objects was consistently the slowest of the four approaches tested. _Engineers weighing interpreter dispatch strategies can compare these trade-offs and benchmarks on daily.dev._ ### How does the wasm3 WebAssembly interpreter architecture relate to tail-call dispatch techniques? The wasm3 virtual machine uses an architecture where each code block calls its own dispatch function under a direct-threading style, which makes the lexical scope of the code align exactly with the runtime execution scope. This property makes it easier to implement control-flow constructs like exceptions on top of the same tail-call dispatch approach used in stack-machine and register-machine Rust interpreters. _Anyone building a wasm-style interpreter can dig into architecture comparisons like this via daily.dev._ ## Community take How the wider developer community reacted, aggregated from 1 discussion across lobsters (as of 2026-09-14). **TL;DR:** The post has minimal community discussion so far, with no substantive comments to draw signal from. **Sentiment:** 50% positive · 50% mixed · 0% skeptical **By community** - lobsters (mixed): No comments have been posted yet, leaving no community signal beyond the single upvote. **Source threads** - [lobsters](https://lobste.rs/s/bp6bmx/tail_call_interpreters_rust) · 1 points · 0 comments ## Similar posts on daily.dev - [A tail-call interpreter in \(nightly\) Rust](https://daily.dev/posts/a-tail-call-interpreter-in-nightly-rust-v5awwh224) · Matt Keeter · 0 upvotes · 0 comments - [Rust should have stable tail calls](https://daily.dev/posts/rust-should-have-stable-tail-calls-6xibbzdnd) · Lobsters · 8 upvotes · 0 comments - [Rust generics: from Static to Dynamic dispatch](https://daily.dev/posts/rust-generics-from-static-to-dynamic-dispatch-p5yv6gqc4) · Sylvain Kerkour · 4 upvotes · 0 comments - [The Cost of Indirection in Rust](https://daily.dev/posts/the-cost-of-indirection-in-rust-qqz41bkaq) · Hacker News · 23 upvotes · 1 comments --- Tags: [#rust](https://daily.dev/tags/rust), [#virtual-machine](https://daily.dev/tags/virtual-machine) [View this post on daily.dev](https://daily.dev/posts/tail-call-interpreters-in-rust-botv3otev) ```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":"Tail-Call Interpreters in Rust","url":"https://daily.dev/posts/tail-call-interpreters-in-rust-botv3otev","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/tail-call-interpreters-in-rust-botv3otev"},"datePublished":"2026-08-10T12:07:36.598Z","dateModified":"2026-09-14T07:53:45.493Z","description":"A deep dive into implementing four VM dispatch strategies in Rust using the unstable `explicit_tail_calls` feature (`become` keyword): switch dispatch,...","image":"https://media.daily.dev/image/upload/s--P4t4XyoV--/f_auto/v1722860399/public/Placeholder%2001","thumbnailUrl":"https://media.daily.dev/image/upload/s--P4t4XyoV--/f_auto/v1722860399/public/Placeholder%2001","isAccessibleForFree":true,"articleSection":"Hacker News","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Hacker News","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/hn","url":"https://daily.dev/sources/hn"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/tail-call-interpreters-in-rust-botv3otev","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"rust,virtual-machine","timeRequired":"PT19M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Hacker News","item":"https://daily.dev/sources/hn"},{"@type":"ListItem","position":3,"name":"Tail-Call Interpreters in Rust"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/tail-call-interpreters-in-rust-botv3otev#faq","mainEntity":[{"@type":"Question","name":"What does Rust's unstable explicit_tail_calls feature and the become keyword do for writing interpreters?","acceptedAnswer":{"@type":"Answer","text":"The explicit_tail_calls feature lets a function guarantee that a recursive call is compiled as a jump instead of allocating a new stack frame, using the `become` keyword in place of a normal call or return. 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