--- title: For my admin panel I developed an expression... description: A step-by-step guide to building an expression parser in PHP that converts mathematical strings into executable code. The tutorial covers three core phases:... canonical: https://daily.dev/posts/for-my-admin-panel-i-developed-an-expression-parser-before-presenting-it-as-a-library-i-wrote-thi-xigmfjmj8 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: For my admin panel I developed an expression parser. Before presenting it as a library, I wrote this article to explain the fundamentals of how a parser is built: tokenization, Abstract Syntax Tree construction, and finally the parsing process itself. It’s a tutorial for anyone who wants to understand the algorithms behind these concepts. | daily.dev og:description: A step-by-step guide to building an expression parser in PHP that converts mathematical strings into executable code. The tutorial covers three core phases:... og:url: https://daily.dev/posts/for-my-admin-panel-i-developed-an-expression-parser-before-presenting-it-as-a-library-i-wrote-thi-xigmfjmj8 og:image: https://api.daily.dev/og/posts/XiGmFjMj8.png og:image:alt: For my admin panel I developed an expression parser. Before presenting it as a library, I wrote this article to explain the fundamentals of how a parser is built: tokenization, Abstract Syntax Tree construction, and finally the parsing process itself. It’s a tutorial for anyone who wants to understand the algorithms behind these concepts. 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. # For my admin panel I developed an expression parser. Before presenting it as a library, I wrote this article to explain the fundamentals of how a parser is built: tokenization, Abstract Syntax Tree construction, and finally the parsing process itself. It’s a tutorial for anyone who wants to understand the algorithms behind these concepts. **[PHP Dev](https://daily.dev/sources/phpdev)** · [@giuliopandolfelli](https://daily.dev/giuliopandolfelli) · 1 upvotes · 0 comments ## Summary A step-by-step guide to building an expression parser in PHP that converts mathematical strings into executable code. The tutorial covers three core phases: tokenization (splitting strings into numbers and operators while handling unary minus), AST construction (building an Abstract Syntax Tree using a two-pass collapse algorithm to respect operator precedence), and recursive evaluation (executing the tree from leaves to root). Includes complete working code examples demonstrating how to parse and evaluate expressions like "2 + 3 * -4" correctly. ## 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 - [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: [#php](https://daily.dev/tags/php), [#algorithms](https://daily.dev/tags/algorithms), [#compiler](https://daily.dev/tags/compiler), [#recursion](https://daily.dev/tags/recursion) [View this post on daily.dev](https://daily.dev/posts/for-my-admin-panel-i-developed-an-expression-parser-before-presenting-it-as-a-library-i-wrote-thi-xigmfjmj8) ```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/for-my-admin-panel-i-developed-an-expression-parser-before-presenting-it-as-a-library-i-wrote-thi-xigmfjmj8","headline":"For my admin panel I developed an expression parser.\n\nBefore presenting it as a library, I wrote this article\nto explain the fundamentals of how a parser is built:\ntokenization, Abstract Syntax Tree construction,\nand finally the parsing process itself.\n\nIt’s a tutorial for anyone who wants to understand\nthe algorithms behind these concepts.","text":"Shared: Expression Parser in PHP (token → AST → execution)","url":"https://daily.dev/posts/for-my-admin-panel-i-developed-an-expression-parser-before-presenting-it-as-a-library-i-wrote-thi-xigmfjmj8","datePublished":"2026-02-04T16:31:06.015Z","dateModified":"2026-02-04T16:32:10.327Z","author":{"@type":"Person","name":"Giulio Pandolfelli","url":"https://daily.dev/giuliopandolfelli","image":"https://lh3.googleusercontent.com/a/ACg8ocINrVVyLn1LD36mppOFxBNQ0juOOd32sUTWNv9cYZV6kiFxE0or=s96-c","interactionStatistic":{"@type":"InteractionCounter","interactionType":{"@type":"EndorseAction"},"userInteractionCount":340}},"image":"https://media.daily.dev/image/upload/s--1KxV4ohY--/f_auto/v1722860400/public/Placeholder%2007","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":1},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"sharedContent":{"@type":"WebPage","url":"https://api.daily.dev/r/8nvyROtj6"},"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":"For my admin panel I developed an expression parser.\n\nBefore presenting it as a library, I wrote this article\nto explain the fundamentals of how a parser is built:\ntokenization, Abstract Syntax Tree construction,\nand finally the parsing process itself.\n\nIt’s a tutorial for anyone who wants to understand\nthe algorithms behind these concepts."}]} ```