Add documentation comments

Oct 13, 2025 by vinooalluri.com 17 views

Introduction

Understanding Haddock Warnings

Haddock is a tool used to generate documentation for Haskell libraries. When running cabal haddock, it generates a report of warnings and errors that need to be addressed. These warnings can be categorized into several types, including missing documentation, ambiguous identifiers, and out-of-scope identifiers. In this article, we will explore the common types of Haddock warnings, their causes, and how to fix them.

Missing Documentation

What are Missing Documentation Warnings?

Missing documentation warnings occur when Haddock is unable to find documentation for a particular identifier, such as a type or function. This can happen when the documentation is missing or incomplete.

Causes of Missing Documentation Warnings

There are several reasons why Haddock may not be able to find documentation for an identifier. Some common causes include:

Missing documentation comments: Documentation comments are essential for Haddock to generate documentation. If a documentation comment is missing, Haddock will not be able to find documentation for the identifier.
Incomplete documentation comments: Even if a documentation comment is present, it may not be complete. Haddock will not be able to generate documentation if the comment is incomplete.
Incorrect documentation comments: If the documentation comment is incorrect or misleading, Haddock may not be able to generate documentation.

Fixing Missing Documentation Warnings

To fix missing documentation warnings, you need to add documentation comments for the missing identifiers. Here are some steps to follow:

Add documentation comments: Add documentation comments for the missing identifiers. Use the -- | syntax to start a documentation comment.
Complete documentation comments: Make sure the documentation comments are complete and accurate.
Check documentation comments: Check the documentation comments to ensure they are correct and not misleading.

Example

Suppose we have a function traverseF that is missing documentation. We can add a documentation comment as follows:

-- | Traverse a functor over a parameterized type.
traverseF :: FunctorF f => (a -> b) -> f a -> f b
traverseF = fmapF

In this example, we added a documentation comment for the traverseF function using the -- | syntax.

Ambiguous Identifiers

What are Ambiguous Identifiers?

Ambiguous identifiers occur when Haddock is unable to determine which identifier to use due to multiple definitions with the same name.

Causes of Ambiguous Identifiers

There are several reasons why Haddock may not be able to determine which identifier to use. Some common causes include:

Multiple definitions with the same name: If multiple identifiers have the same name, Haddock may not be able to determine which one to use.
Incorrect imports: If the imports are incorrect or incomplete, Haddock may not be able to determine which identifier to use.

Fixing Ambiguous Identifiers

To fix ambiguous identifiers, you need to disambiguate the identifiers. Here are some steps to follow:

Qualify identifiers: Qualify the identifiers by using the module name or the type/value namespace explicitly.
Specify the type/value namespace: Specify the type/value namespace explicitly to disambiguate the identifiers.
Check imports: Check the imports to ensure they are correct and complete.

Example

Suppose we have two identifiers Some defined in different modules. We can disambiguate the identifiers as follows:

-- Import the first Some module
import Data.Parameterized.Some1 (Some)

-- Import the second Some module
import Data.Parameterized.Some2 (Some)

-- Use the qualified identifier
qualified Some = Some1.Some

In this example, we qualified the Some identifier by using the module name Some1 and Some2.

Out-of-Scope Identifiers

What are Out-of-Scope Identifiers?

Out-of-scope identifiers occur when Haddock is unable to find an identifier because it is not in scope.

Causes of Out-of-Scope Identifiers

There are several reasons why Haddock may not be able to find an identifier. Some common causes include:

Missing imports: If the imports are missing or incomplete, Haddock may not be able to find the identifier.
Incorrect imports: If the imports are incorrect or incomplete, Haddock may not be able to find the identifier.

Fixing Out-of-Scope Identifiers

To fix out-of-scope identifiers, you need to add the missing imports or correct the incorrect imports. Here are some steps to follow:

Add missing imports: Add the missing imports to ensure the identifier is in scope.
Correct incorrect imports: Correct the incorrect imports to ensure the identifier is in scope.

Example

Suppose we have an identifier fmapF that is out of scope. We can add the missing import as follows:

-- Import the fmapF function
import Data.Parameterized.TraversableFC (fmapF)

-- Use the fmapF function
fmapF :: FunctorF f => (a -> b) -> f a -> f b

In this example, we added the missing import for the fmapF function.

Conclusion

In this article, we explored the common types of Haddock warnings, their causes, and how to fix them. We discussed missing documentation warnings, ambiguous identifiers, and out-of-scope identifiers. We provided examples and steps to follow to fix these warnings. By following these steps, you can ensure your Haskell code is well-documented and free of Haddock warnings.

Additional Resources

Step-by-Step Guide

Step 1: Run `cabal haddock`

Run cabal haddock to generate the Haddock report.

Step 2: Review the Haddock report

Review the Haddock report to identify the warnings.

Step 3: Fix the warnings

Fix the warnings by following the steps outlined in this article.

Step 4: Run `cabal haddock` again

Run cabal haddock again to verify that the warnings are fixed.

Step 5: Commit the changes

Commit the changes to your code repository.

Step 6: Push the changes

Push the changes to your code repository.

Step 7: Verify the changes

Verify the changes by running cabal haddock again.

By following these steps, you can ensure your Haskell code is well-documented and free of Haddock warnings.

Introduction

Understanding Haddock Warnings

Haddock is a tool used to generate documentation for Haskell libraries. When running cabal haddock, it generates a report of warnings and errors that need to be addressed. These warnings can be categorized into several types, including missing documentation, ambiguous identifiers, and out-of-scope identifiers. In this article, we will answer some frequently asked questions about Haddock warnings and how to fix them.

Q&A

Q: What are Haddock warnings?

A: Haddock warnings are messages generated by the Haddock tool when it encounters issues with the documentation of a Haskell library. These warnings can be categorized into several types, including missing documentation, ambiguous identifiers, and out-of-scope identifiers.

Q: Why do I get Haddock warnings?

A: You get Haddock warnings because the Haddock tool is unable to find documentation for certain identifiers, or because the documentation is incomplete or incorrect. This can happen due to missing documentation comments, incorrect documentation comments, or incorrect imports.

Q: How do I fix Haddock warnings?

A: To fix Haddock warnings, you need to add documentation comments for the missing identifiers, complete the documentation comments, and correct the incorrect imports. You can also use the -- | syntax to start a documentation comment.

Q: What is the difference between a missing documentation warning and an ambiguous identifier warning?

A: A missing documentation warning occurs when Haddock is unable to find documentation for a particular identifier. An ambiguous identifier warning occurs when Haddock is unable to determine which identifier to use due to multiple definitions with the same name.

Q: How do I disambiguate an ambiguous identifier?

A: To disambiguate an ambiguous identifier, you need to qualify the identifier by using the module name or the type/value namespace explicitly. You can also specify the type/value namespace explicitly to disambiguate the identifiers.

Q: What is the difference between an out-of-scope identifier warning and an ambiguous identifier warning?

A: An out-of-scope identifier warning occurs when Haddock is unable to find an identifier because it is not in scope. An ambiguous identifier warning occurs when Haddock is unable to determine which identifier to use due to multiple definitions with the same name.

Q: How do I fix an out-of-scope identifier warning?

A: To fix an out-of-scope identifier warning, you need to add the missing imports or correct the incorrect imports. You can also use the import statement to import the necessary modules.

Q: Can I ignore Haddock warnings?

A: No, you should not ignore Haddock warnings. Haddock warnings indicate issues with the documentation of your Haskell library, and ignoring them can lead to poor documentation and confusion for users.

Q: How do I enable more strict form of checking for Haddock warnings?

A: To enable more strict form of checking for Haddock warnings, you can use the --strict flag when running cabal haddock. This will enable more strict form of checking for Haddock warnings.

Q: Can I customize the Haddock report?

A: Yes, you can customize the Haddock report by using the --output flag when running cabal haddock. This will allow you to specify the output file for the Haddock report.

Q: How do I verify that the Haddock warnings are fixed?

A: To verify that the Haddock warnings are fixed, you can run cabal haddock again and check the Haddock report to ensure that the warnings are no longer present.

Conclusion

In this article, we answered some frequently asked questions about Haddock warnings and how to fix them. We discussed missing documentation warnings, ambiguous identifiers, and out-of-scope identifiers, and provided examples and steps to follow to fix these warnings. By following these steps, you can ensure your Haskell code is well-documented and free of Haddock warnings.

Additional Resources

Step-by-Step Guide

Step 1: Run `cabal haddock`

Run cabal haddock to generate the Haddock report.

Step 2: Review the Haddock report

Review the Haddock report to identify the warnings.

Step 3: Fix the warnings

Fix the warnings by following the steps outlined in this article.

Step 4: Run `cabal haddock` again

Run cabal haddock again to verify that the warnings are fixed.

Step 5: Commit the changes

Commit the changes to your code repository.

Step 6: Push the changes

Push the changes to your code repository.

Step 7: Verify the changes

Verify the changes by running cabal haddock again.

By following these steps, you can ensure your Haskell code is well-documented and free of Haddock warnings.