--- id: video/ADXkUFI_VWI type: video title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" summary: "AL compiler internals and history, from the C/SIDE era to today: Roslyn-based design, partial compilation and LSP for Visual Studio Code, transpiling AL to C#, and the unsupported, undocumented state of the compiler API. Also covers prototype VS Code designers and AL Explorer." tier: official language: en tags: - al compiler - compiler architecture - roslyn - language service protocol - visual studio code - c-side history - symbol references - partial compilation - intellisense - background compilation - transpiler - c# code generation system: development review: state: reviewed by: opus at: "2026-10-07T23:11:35.295Z" flags: [] generated: at: "2026-10-07T23:11:35.349Z" pipeline: 0.2.0 prompts: extract-video: 1 summarize-video: 2 input_hash: e7b937d33358fb9ff1ecdd736cacee4d43affc2be1cb8da21d6ac4a8f108a07c evidence: - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=399s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 399 quote: In 2019, in wave two, we shipped the first AL compiler without the preview mark on it, and then at that time we could - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=466s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 466 quote: they realized that they already have a. They have one compiler for a command line and almost a similar compiler that were used inside - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=490s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 490 quote: the same compiler, the same base part of the compiler that serves the command line compilation is also the one that constantly runs in - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=538s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 538 quote: It's not Roslyn, but we have moved a lot of the concepts out of the Roslyn code base because we are not. - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=563s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 563 quote: we have way more concepts than C# for instance. So in some some sense we are more complicated because we have I mean 7-8 - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=687s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 687 quote: we also realized that we could easily repurpose A compiler to another environment if we had to. But turned out that best decision ever - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=804s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 804 quote: it's textbook to create a compiler that has a perfect source, but but having a source where you are typing something in the middle - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=868s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 868 quote: They actually invented what is called the Language Service Protocol exactly for this - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=941s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 941 quote: One of the reasons is that we we we need a sandbox language. Since we are running third party code on our servers, we - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1008s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 1008 quote: This is a language that's been written for for ERP and for Business Central. Exactly. But the most important part of this was that - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1088s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 1088 quote: We are converting AL to C#. Is that a good idea? Yes, I think for us it is - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1190s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 1190 quote: compiler the code is actually saved in text file like any like many other languages - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1540s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 1540 quote: That's still a prototype. Right, still a prototype. I would love us to prioritize them, but again, we need to prioritize. - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1574s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 1574 quote: They would like to be able to use it to do all sorts of things and some people actually doing it already in a - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1588s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 1588 quote: It's envisioned as a service we haven't officially opened up for. New for for external use means that we haven't documented it - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1611s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 1611 quote: We're not preventing it. We're not just supporting it and we we reserve ourselves the right to change it at any time. - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1635s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 1635 quote: Already incredibly many AL related extensions in the Visual Studio Code Marketplace, which is amazing to see - kind: video url: https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1671s title: "Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler" date: "2024-03-27T12:00:02.000Z" commit: null t: 1671 quote: There's of course our own documentation on Ms. learning, which is both a combination of reference documentation but also getting started documentation. links: learn: [] objects: [] features: [] topics: [] localizations: [] videos: [] posts: [] guidelines: [] video_id: ADXkUFI_VWI channel: yt-microsoft source_name: Microsoft Dynamics 365 Business Central (YouTube) url: https://www.youtube.com/watch?v=ADXkUFI_VWI published_at: "2024-03-27T12:00:02.000Z" duration_s: 1751 captions: full audience: - developer - partner - decision maker chapters: - t: 0 title: "History: C-side and the 2T architecture" - t: 122 title: Challenges with C-side and the modernization vision - t: 233 title: The prototype and symbol reference strategy - t: 363 title: Early previews and the journey to GA - t: 429 title: Roslyn architecture and the compiler design - t: 549 title: AL language concepts and the perfect storm timing - t: 672 title: Visual Studio Code adoption and language service architecture - t: 797 title: Partial compilation, LSP protocol, and extensibility - t: 927 title: Why AL instead of existing languages - t: 1008 title: AL transpiler and code generation to C# - t: 1154 title: Migration from C/SIDE to AL and text-based development - t: 1326 title: Visual Studio Code designers and AL Explorer - t: 1553 title: Compiler API exposure and getting started features: - name: AL compiler status: unclear t: 8 verified: false status_source: video - name: Partial compilation and recovery status: unclear t: 783 verified: false status_source: video - name: Language Service Protocol support status: unclear t: 731 verified: false status_source: video - name: Symbol reference information wrapping status: unclear t: 233 verified: false status_source: video - name: AL transpiler to C# status: unclear t: 1008 verified: false status_source: video - name: Text-based source code storage status: unclear t: 1154 verified: false status_source: video - name: AL Explorer status: unclear t: 1326 verified: false status_source: video - name: AL Home status: unclear t: 1326 verified: false status_source: video - name: Visual Studio Code designers status: unclear t: 1516 verified: false status_source: video - name: Compiler API exposure status: unclear t: 1553 verified: false status_source: video - name: AL extensions in Visual Studio Code marketplace status: unclear t: 1635 verified: false status_source: video objects_mentioned: - codeunit safe post code unit - other AL Explorer - other AL Home - other Visual Studio Code Marketplace quotes: - t: 399 text: In 2019, in wave two, we shipped the first AL compiler without the preview mark on it, and then at that time we could check: exact - t: 466 text: they realized that they already have a. They have one compiler for a command line and almost a similar compiler that were used inside check: exact - t: 490 text: the same compiler, the same base part of the compiler that serves the command line compilation is also the one that constantly runs in check: exact - t: 538 text: It's not Roslyn, but we have moved a lot of the concepts out of the Roslyn code base because we are not. check: exact - t: 563 text: we have way more concepts than C# for instance. So in some some sense we are more complicated because we have I mean 7-8 check: exact - t: 687 text: we also realized that we could easily repurpose A compiler to another environment if we had to. But turned out that best decision ever check: exact - t: 804 text: it's textbook to create a compiler that has a perfect source, but but having a source where you are typing something in the middle check: exact - t: 868 text: They actually invented what is called the Language Service Protocol exactly for this check: exact - t: 941 text: One of the reasons is that we we we need a sandbox language. Since we are running third party code on our servers, we check: exact - t: 1008 text: This is a language that's been written for for ERP and for Business Central. Exactly. But the most important part of this was that check: exact - t: 1088 text: We are converting AL to C#. Is that a good idea? Yes, I think for us it is check: exact - t: 1190 text: compiler the code is actually saved in text file like any like many other languages check: fuzzy - t: 1540 text: That's still a prototype. Right, still a prototype. I would love us to prioritize them, but again, we need to prioritize. check: exact - t: 1574 text: They would like to be able to use it to do all sorts of things and some people actually doing it already in a check: exact - t: 1588 text: It's envisioned as a service we haven't officially opened up for. New for for external use means that we haven't documented it check: exact - t: 1611 text: We're not preventing it. We're not just supporting it and we we reserve ourselves the right to change it at any time. check: exact - t: 1635 text: Already incredibly many AL related extensions in the Visual Studio Code Marketplace, which is amazing to see check: exact - t: 1671 text: There's of course our own documentation on Ms. learning, which is both a combination of reference documentation but also getting started documentation. check: exact --- # Business Central Under the Hood episode 2: The Inner Workings of The AL Compiler > AL compiler internals and history, from the C/SIDE era to today: Roslyn-based design, partial compilation and LSP for Visual Studio Code, transpiling AL to C#, and the unsupported, undocumented state of the compiler API. Also covers prototype VS Code designers and AL Explorer. [Watch on YouTube](https://www.youtube.com/watch?v=ADXkUFI_VWI) · Microsoft Dynamics 365 Business Central (YouTube) · 2024-03-27 · 29:11 · tier official · reviewed (checked by Opus) ## Overview Episode 2 of Business Central Under the Hood (published 2024-03-27, 29 minutes) walks through how the AL compiler came about and how it works. It starts with C/SIDE and its two-tier architecture, the prototype that wrapped the old base app in symbol references, and the years of early previews before the first AL compiler shipped without a preview mark in 2019 wave two. It then covers the design: Roslyn concepts, a compiler-as-a-service that also drives the language server, partial compilation with error recovery, and the Language Service Protocol used with Visual Studio Code. It explains why AL was built instead of reusing an existing language, why AL is transpiled to C#, and what moving to text files meant. It closes with the VS Code designers prototype, AL Explorer, AL Home, and the status of the compiler API. ## Key points - The AL compiler uses Roslyn architecture concepts. The same base compiler serves command-line compilation and the background compilation that runs in the editor. - Partial compilation with error recovery gives intellisense while code is incomplete. Results are reused to keep memory use down and avoid recompiling unchanged code. - The editor and the AL language server communicate through the Language Service Protocol. - AL is transpiled to C#, and the generated C# is compiled with the regular C# compiler. Metadata is stored in XML and the database. - A sandbox language was one stated reason for AL, because third-party code runs on Microsoft's servers. - Moving to text-file source enabled Git, search tools and standard source control. It also fit the cloud, where requiring a direct database connection is a bad idea. The C/SIDE visual designers were lost, and VS Code designers are only a prototype. - The compiler API is not officially supported or documented, and may change at any time. Partners already use it in unsupported ways. ## Chapters - [0:00](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=0s) History: C-side and the 2T architecture - [2:02](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=122s) Challenges with C-side and the modernization vision - [3:53](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=233s) The prototype and symbol reference strategy - [6:03](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=363s) Early previews and the journey to GA - [7:09](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=429s) Roslyn architecture and the compiler design - [9:09](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=549s) AL language concepts and the perfect storm timing - [11:12](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=672s) Visual Studio Code adoption and language service architecture - [13:17](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=797s) Partial compilation, LSP protocol, and extensibility - [15:27](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=927s) Why AL instead of existing languages - [16:48](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1008s) AL transpiler and code generation to C# - [19:14](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1154s) Migration from C/SIDE to AL and text-based development - [22:06](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1326s) Visual Studio Code designers and AL Explorer - [25:53](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1553s) Compiler API exposure and getting started ## Features | Feature | Status | At | |---|---|---| | AL compiler | status not stated | [0:08](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=8s) | | Partial compilation and recovery | status not stated | [13:03](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=783s) | | Language Service Protocol support | status not stated | [12:11](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=731s) | | Symbol reference information wrapping | status not stated | [3:53](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=233s) | | AL transpiler to C# | status not stated | [16:48](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1008s) | | Text-based source code storage | status not stated | [19:14](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1154s) | | AL Explorer | status not stated | [22:06](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1326s) | | AL Home | status not stated | [22:06](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1326s) | | Visual Studio Code designers | status not stated, demoed | [25:16](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1516s) | | Compiler API exposure | status not stated | [25:53](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1553s) | | AL extensions in Visual Studio Code marketplace | status not stated | [27:15](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1635s) | ## AL objects mentioned As heard in the captions. A name that matches one object page by exact type and name links to it; the others stay as named. - codeunit "safe post code unit" at [4:18](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=258s) - other "AL Explorer" at [24:12](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1452s) - other "AL Home" at [24:48](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1488s) - other "Visual Studio Code Marketplace" at [27:15](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1635s) Not found in BC28-30: codeunit "safe post code unit". ## Quotes - [6:39](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=399s) "In 2019, in wave two, we shipped the first AL compiler without the preview mark on it, and then at that time we could" - [7:46](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=466s) "they realized that they already have a. They have one compiler for a command line and almost a similar compiler that were used inside" - [8:10](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=490s) "the same compiler, the same base part of the compiler that serves the command line compilation is also the one that constantly runs in" - [8:58](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=538s) "It's not Roslyn, but we have moved a lot of the concepts out of the Roslyn code base because we are not." - [9:23](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=563s) "we have way more concepts than C# for instance. So in some some sense we are more complicated because we have I mean 7-8" - [11:27](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=687s) "we also realized that we could easily repurpose A compiler to another environment if we had to. But turned out that best decision ever" - [13:24](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=804s) "it's textbook to create a compiler that has a perfect source, but but having a source where you are typing something in the middle" - [14:28](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=868s) "They actually invented what is called the Language Service Protocol exactly for this" - [15:41](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=941s) "One of the reasons is that we we we need a sandbox language. Since we are running third party code on our servers, we" - [16:48](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1008s) "This is a language that's been written for for ERP and for Business Central. Exactly. But the most important part of this was that" - [18:08](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1088s) "We are converting AL to C#. Is that a good idea? Yes, I think for us it is" - [19:50](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1190s) "compiler the code is actually saved in text file like any like many other languages" - [25:40](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1540s) "That's still a prototype. Right, still a prototype. I would love us to prioritize them, but again, we need to prioritize." - [26:14](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1574s) "They would like to be able to use it to do all sorts of things and some people actually doing it already in a" - [26:28](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1588s) "It's envisioned as a service we haven't officially opened up for. New for for external use means that we haven't documented it" - [26:51](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1611s) "We're not preventing it. We're not just supporting it and we we reserve ourselves the right to change it at any time." - [27:15](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1635s) "Already incredibly many AL related extensions in the Visual Studio Code Marketplace, which is amazing to see" - [27:51](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1671s) "There's of course our own documentation on Ms. learning, which is both a combination of reference documentation but also getting started documentation." ## Disclaimers in the video - [6:03](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=363s) preview: early previews of it. And we did that for a couple of years, and the initial one was only we could create simple code units, simple tables, pages. - [25:40](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1540s) preview: That's still a prototype - [25:53](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1553s) preview: It's still the prototype label - [26:28](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1588s) preview: It's envisioned as a service we haven't officially opened up for. New for for external use means that we haven't documented it - [26:51](https://www.youtube.com/watch?v=ADXkUFI_VWI&t=1611s) subject-to-change: We reserve ourselves the right to change it at any time Presenters (as heard): Espen.