--- title: Expression Parser in PHP (tokens → AST → execution) description: A walkthrough of building a mathematical expression parser in PHP covering three stages: tokenization (splitting a string into numbers and operators), AST... canonical: https://daily.dev/posts/y2waydu0p twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Expression Parser in PHP (tokens → AST → execution) | daily.dev og:description: A walkthrough of building a mathematical expression parser in PHP covering three stages: tokenization (splitting a string into numbers and operators), AST... og:url: https://daily.dev/posts/y2waydu0p og:image: https://api.daily.dev/og/posts/Y2WaYDU0p.png og:image:alt: Post cover image 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. # Expression Parser in PHP (tokens → AST → execution) **[PHP Dev](https://daily.dev/sources/phpdev)** · [@danielpetrica](https://daily.dev/danielpetrica) · 1 upvotes · 0 comments ## Summary A walkthrough of building a mathematical expression parser in PHP covering three stages: tokenization (splitting a string into numbers and operators), AST construction (building a nested tree that respects operator precedence via a two-pass collapse approach), and recursive execution of the resulting tree. Includes handling of unary minus, complete PHP code for each step, and a working CLI example producing correct results like `2 + 3 * -4 = -10`. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Parsing: How Ruby Understands Your Code](https://daily.dev/posts/parsing-how-ruby-understands-your-code-flstsejne) · RUBYLAND · 0 upvotes · 0 comments - [The Code Started Writing Itself After Thinking Like a Program Instead of a Human](https://daily.dev/posts/the-code-started-writing-itself-after-thinking-like-a-program-instead-of-a-human-5vxqsapej) · Medium · 0 upvotes · 0 comments - [Let's make a programming language. Parser](https://daily.dev/posts/let-s-make-a-programming-language-parser-ddrko7v9u) · C\+\+ · 0 upvotes · 0 comments - [Inverse parentheses](https://daily.dev/posts/inverse-parentheses-bythjpogi) · Lobsters · 0 upvotes · 0 comments - [Let’s make a programming language. AST — Key points](https://daily.dev/posts/let-s-make-a-programming-language-ast-key-points-r0hhj9ndy) · Medium · 0 upvotes · 0 comments --- Tags: [#nlp](https://daily.dev/tags/nlp), [#php](https://daily.dev/tags/php) [View this post on daily.dev](https://daily.dev/posts/y2waydu0p) ```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":"DiscussionForumPosting","mainEntityOfPage":"https://daily.dev/posts/y2waydu0p","headline":"Expression Parser in PHP (tokens → AST → execution)","text":"Shared: Expression Parser in PHP (tokens → AST → execution)","url":"https://daily.dev/posts/y2waydu0p","datePublished":"2026-03-18T09:36:57.783Z","dateModified":"2026-03-18T09:36:57.793Z","author":{"@type":"Person","name":"Daniel, Petrica Andrei-Daniel","url":"https://daily.dev/danielpetrica","image":"https://avatars.githubusercontent.com/u/4850686?v=4","description":"Featured Laravel Artisan, DevOps & New Relic Consultant | Building Scalable Systems with Precision \n","interactionStatistic":{"@type":"InteractionCounter","interactionType":{"@type":"EndorseAction"},"userInteractionCount":2020}},"image":"https://media.daily.dev/image/upload/s--OHB84bZF--/f_auto/v1722860399/public/Placeholder%2010","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":1},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"sharedContent":{"@type":"WebPage","url":"https://api.daily.dev/r/ZPd1waXBs"},"isPartOf":{"@type":"WebPage","url":"https://daily.dev/squads/phpdev","name":"PHP Dev"}} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"PHP Dev","item":"https://daily.dev/squads/phpdev"},{"@type":"ListItem","position":3,"name":"Expression Parser in PHP (tokens → AST → execution)"}]} ```