How does Atlas handle F# file order for stack traces?

Atlas explicitly reads your F# .fsproj file to understand the correct compilation and file order. This ensures that when it processes a stack trace, it interprets the context of each line within the F# codebase accurately, which is crucial for F# projects.

Can Atlas use my local Ollama embeddings for F# code?

Yes, Atlas can build its code index with local Ollama embeddings. This capability allows F# developers to keep their proprietary code off third-party servers, ensuring privacy while still benefiting from Atlas's hybrid semantic and keyword retrieval for F# code.

What F# testing frameworks does Atlas support?

Atlas integrates directly with the dotnet test runner, specifically supporting F# testing frameworks like Expecto. It can add new Expecto tests to your test project and run them behind a permission prompt to verify bug fixes.

How does Atlas ensure safety when modifying F# code?

Atlas employs multiple safety layers. Every tool call, including edit for F# files, is permission-gated. It drafts plans in a read-only agent, asks for approval before executing, and computes a unified diff for every file edit, which you must approve before writing to disk.

Does Atlas integrate with F# formatting tools like Fantomas?

Yes, Atlas integrates with fantomas. After making changes to F# source files, you can instruct Atlas to run fantomas over the modified .fs files, ensuring that your codebase maintains consistent formatting standards automatically.

Can Atlas help me refactor F# code, like replacing null checks?

Absolutely. Atlas can assist with F# refactoring tasks. For instance, you can ask Atlas to replace a null check with an F# Option pipeline, leveraging its understanding of F# idioms and AST declarations to propose idiomatic and safer code.

How does Atlas handle F# discriminated unions and computation expressions?

Atlas indexes code by AST declarations using tree-sitter, giving it a deep understanding of F# constructs like discriminated unions, modules, and computation expressions. This allows its lsp tool to accurately find references and understand code context within complex F# patterns.

What if my F# stack trace is from an older build?

Atlas's read tool validates line offsets against the current file. If it detects an 'Offset is out of range' error for an F# file, it will loudly report that the trace is from a different build, advising you to re-read the file from the top before trusting any line numbers.

Trace a runtime bug from a stack trace in F# with Atlas in 2026

In 2026, F# developers can leverage Atlas to efficiently trace a runtime bug from a production stack trace to its root cause and implement a fix, all without the need for an attached debugger. Atlas direct integrates with the F# toolchain, understanding .fsproj file order, discriminated unions, and interacting directly with dotnet test (Expecto) for regression testing and fantomas for code formatting.

How does Atlas trace F# runtime bugs from stack traces?

Atlas traces F# runtime bugs by consuming a raw stack trace, which is a list of file:line pairs, and using its read tool to examine each frame at its reported offset. This process, available in 2026, respects the crucial file order defined in your F# .fsproj file, ensuring accurate context for every line of code.

When an F# application throws an exception in production, the resulting stack trace provides file paths and line numbers. Atlas's read tool is designed to consume this information directly. For each frame in the stack trace, Atlas reads the specified F# source file (.fs or .fsi) at the reported line offset. Unlike generic text editors, Atlas builds its code index using tree-sitter, understanding F# AST declarations like modules, functions, and discriminated unions. This deep understanding, combined with reading the .fsproj file to respect F#’s compilation order, allows Atlas to accurately interpret the context of the failing line. If the stack trace omits callers, Atlas can use grep to find them, reconstructing the full execution path leading to the bug. This initial read operation is the foundation for all subsequent debugging steps, providing a precise starting point within your F# codebase.

How does Atlas validate F# stack traces for build consistency?

Atlas rigorously validates F# stack trace offsets against the current file content, a critical step in 2026 to prevent misdiagnosis from outdated builds. If the read tool reports 'Offset <n> is out of range for this file,' it immediately signals that the trace originated from a different build, prompting a re-read from the top.

A common pitfall when debugging production issues is using a stack trace generated from an older or different build than the codebase currently being examined. Atlas addresses this directly by validating every reported line offset. When Atlas's read tool attempts to access a specific line in an F# source file, it first checks if that offset is within the current file's bounds. If the read tool reports 'Offset <n> is out of range for this file,' it's a clear, loud failure indicating a mismatch. In such a scenario, Atlas advises the F# developer to re-read the file from the top before trusting any line number from the potentially stale trace. This robust validation mechanism ensures that any subsequent analysis, such as finding references or applying fixes, is based on the correct, current version of the F# code, preventing wasted effort and incorrect assumptions.

How does Atlas find the root cause in F# using grep and lsp?

After validating the stack trace, Atlas employs its grep tool to locate the error message string, often revealing where the error is constructed, which is more informative than the top frame. Subsequently, in 2026, the lsp tool's findReferences operation is used on the failing F# function, respecting discriminated unions and modules, to identify callers that might supply bad input.

Once Atlas has accurately located the initial failing line in an F# file, the next step is to pinpoint the true root cause. The grep tool is invaluable here; by searching for the exact error message string from the stack trace, Atlas can often find the location where the error message is constructed. This is frequently more insightful than just the top frame, as it reveals the conditions under which the error is generated. Following this, Atlas leverages its lsp (Language Server Protocol) tool, which understands F# semantics. The findReferences operation is executed on the identified failing F# function or member. Because Atlas indexes code by AST declarations using tree-sitter, it can accurately find all callers, even those involving complex F# constructs like discriminated unions or computation expressions. This allows the F# developer to trace back through the call chain, identifying which inputs or states lead to the erroneous behavior, without needing to manually work through the codebase.

How does Atlas fix F# bugs and add regression tests?

Atlas facilitates fixing F# bugs using its edit tool, allowing developers to draft changes directly. After applying a fix, Atlas can add a regression test to the F# test project, typically using Expecto with dotnet test, ensuring the bug cannot recur silently. This process, available in 2026, includes reviewing a unified diff before committing.

With the root cause identified, Atlas assists in applying the fix. The edit tool allows the F# developer to draft the necessary code changes. Atlas computes a unified diff for every file edit, surfacing it for approval before writing, ensuring transparency and control. A crucial part of any bug fix is preventing its recurrence. Atlas can then be instructed to add a regression test. For F# projects, this typically involves adding new tests to the test project, often leveraging the Expecto test runner. Atlas can run dotnet test behind a permission prompt, executing the newly added tests to verify the fix. Furthermore, Atlas can be asked to replace a null check with an F# Option pipeline, or to ensure that fantomas is run over the changed .fs files to maintain code style consistency. This comprehensive approach ensures not only that the bug is fixed, but also that the F# codebase remains robust and well-tested.

What are Atlas's safety and review mechanisms for F# code changes?

Atlas incorporates robust safety and review mechanisms for F# code changes, ensuring developer control in 2026. Every Atlas tool call, including edit or dotnet test, is permission-gated against allow, ask, and deny rules. Atlas drafts a plan in a read-only agent and computes a unified diff for every file edit, which is surfaced for approval before writing.

Atlas is designed with developer control and safety as paramount concerns, especially when modifying critical F# codebases. Before any tool call, such as edit to modify an .fs file or running dotnet test (Expecto), Atlas checks against permission-gated allow, ask, and deny rules. This means an F# developer always has the final say on what actions Atlas takes. Furthermore, Atlas operates with a clear separation of concerns: it first drafts a plan in a read-only plan agent, presenting its proposed steps. Only after explicit approval does it switch to a build agent to execute changes. For every file modification, Atlas computes a unified diff, which is then presented to the user for approval. This allows F# developers to review exactly what changes Atlas proposes before they are written to disk. Atlas also reads git branches, status, and diffs, and can stage and create commits on your behalf, even snapshotting file changes as git patches for easy rollback, providing multiple layers of safety and review for F# development.

Step by step

01Paste the F# stack trace into Atlas: Begin by pasting the full production stack trace into the Atlas terminal. Atlas's read tool will automatically parse the file:line pairs.
02Review read output for F# offset validation: Observe Atlas's read tool output. If it reports 'Offset <n> is out of range for this file' for an F# source file, the trace is from an older build. Re-read the file from the top before proceeding.
03grep for the error message in F# files: Instruct Atlas to grep for the specific error message string from the stack trace across your F# codebase. This often reveals where the error is constructed, providing more context than just the top frame.
04Use lsp findReferences on the failing F# function: Once a likely failing F# function is identified, use Atlas's lsp tool with the findReferences operation on that function. Atlas will leverage its understanding of F# AST declarations, including discriminated unions, to show all callers that could lead to the bad input.
05Draft a fix with Atlas's edit tool: Collaborate with Atlas using its edit tool to draft the necessary changes in the F# source file. For example, you might ask Atlas to replace a null check with an F# Option pipeline.
06Approve the edit and run dotnet test (Expecto): Review the unified diff presented by Atlas for the proposed F# code changes. After approval, instruct Atlas to add a regression test to your F# test project and run dotnet test (Expecto) to verify the fix.
07Review the unified diff and approve the commit: Atlas will present a unified diff of all changes, including the new F# test. Review these changes carefully. Once satisfied, approve the commit, and Atlas will stage and create a git commit on your behalf.
08Have Atlas run fantomas on changed .fs files: Finally, ask Atlas to run fantomas over the changed .fs files to ensure all new or modified F# code adheres to your project's formatting standards.

Frequently asked questions

How does Atlas handle F# file order for stack traces?: Atlas explicitly reads your F# .fsproj file to understand the correct compilation and file order. This ensures that when it processes a stack trace, it interprets the context of each line within the F# codebase accurately, which is crucial for F# projects.
Can Atlas use my local Ollama embeddings for F# code?: Yes, Atlas can build its code index with local Ollama embeddings. This capability allows F# developers to keep their proprietary code off third-party servers, ensuring privacy while still benefiting from Atlas's hybrid semantic and keyword retrieval for F# code.
What F# testing frameworks does Atlas support?: Atlas integrates directly with the dotnet test runner, specifically supporting F# testing frameworks like Expecto. It can add new Expecto tests to your test project and run them behind a permission prompt to verify bug fixes.
How does Atlas ensure safety when modifying F# code?: Atlas employs multiple safety layers. Every tool call, including edit for F# files, is permission-gated. It drafts plans in a read-only agent, asks for approval before executing, and computes a unified diff for every file edit, which you must approve before writing to disk.
Does Atlas integrate with F# formatting tools like Fantomas?: Yes, Atlas integrates with fantomas. After making changes to F# source files, you can instruct Atlas to run fantomas over the modified .fs files, ensuring that your codebase maintains consistent formatting standards automatically.
Can Atlas help me refactor F# code, like replacing null checks?: Absolutely. Atlas can assist with F# refactoring tasks. For instance, you can ask Atlas to replace a null check with an F# Option pipeline, leveraging its understanding of F# idioms and AST declarations to propose idiomatic and safer code.
How does Atlas handle F# discriminated unions and computation expressions?: Atlas indexes code by AST declarations using tree-sitter, giving it a deep understanding of F# constructs like discriminated unions, modules, and computation expressions. This allows its lsp tool to accurately find references and understand code context within complex F# patterns.
What if my F# stack trace is from an older build?: Atlas's read tool validates line offsets against the current file. If it detects an 'Offset <n> is out of range' error for an F# file, it will loudly report that the trace is from a different build, advising you to re-read the file from the top before trusting any line numbers.

Try Atlas in your terminal

The terminal-native AI coding agent. Free core, single binary.

Install Atlas

Related guides

Trace a Runtime Bug from a Stack Trace with Atlas in 2026

How to trace a runtime bug from a stack trace with Atlas in 2026: read each frame at its offset, grep for the error string, and use the lsp tool to find callers.

Atlas for F#: A Terminal-Native AI Coding Agent for .fsproj Solutions in 2026

Atlas is a terminal-native AI coding agent for F# in 2026. It respects .fsproj file order, maps discriminated unions, runs dotnet test behind a prompt, and runs Fantomas.

Document a module with a README in F# with Atlas in 2026

Generate accurate, up-to-date READMEs for your F# modules using Atlas in 2026. Atlas leverages your .fsproj and real code to document public APIs, ensuring documentation reflects current implementation, not outdated

Review a Pull Request in F# with Atlas in 2026

In 2026, F# developers use Atlas to review pull requests, leveraging its deep understanding of .fsproj files, discriminated unions, and dotnet test (Expecto) to catch subtle bugs.

Refactor a legacy F# module with Atlas in 2026

Safely refactor legacy F# modules using Atlas, the terminal-native AI coding agent. Pin behavior with `dotnet test (Expecto)`, apply changes, and ensure F# code quality with `fantomas`.

Upgrade a Dependency and Fix Breakage in F# with Atlas in 2026

Upgrade F# dependencies in 2026 with Atlas. direct bump NuGet packages, fix compile errors, and repair Expecto test failures using dotnet add package and fantomas for a smooth migration.

Run Atlas Headless in CI for F# Projects in 2026

F# developers in 2026 can run Atlas headless in CI pipelines to automate code tasks. Get machine-readable output, integrate with dotnet test (Expecto), NuGet, and fantomas for robust F# development.

Extract a Shared Helper from Duplicated F# Code with Atlas in 2026

Refactor F# code in 2026 by extracting duplicated logic into a shared helper using Atlas. Leverage semantic search, automated refactoring, and F#-specific toolchain integration for clean, tested code.

Browse this resource hub