Please feel free to open an issue for any questions, suggestions, issues or bugs in the library. In case you are reporting a bug we will appreciate if you provide as much detail as possible to reproduce or understand the problem, but nevertheless you are encouraged to open an issue for any problem that you may encounter.
Beginners are encouraged to pick up issues that are marked help wanted. It is
a good idea to update the issue expressing your intent so that others do not
duplicate the effort and people with a background on the issue can help.
Some common commands:
$ cabal repl
$ cabal build
$ cabal build --disable-optimization --flags -opt
$ bin/test.sh --quick
$ bin/bench.sh --quick # For nix use "--use-nix"
$ bin/run-ci --targets help # Only supported with nix
$ cabal haddock
$ cabal-docspec --timeout 60 --check-properties --property-variables xs
The bin/test.sh and bin/bench.sh are custom scripts to perform test
and benchmarking tasks conveniently. They support running a group of
tests or benchmarks, coverage, using correct optimization flags for
benchmarking, benchmark comparison reports etc. Use the --help option
to see how to use these. See benchmark/README.md
and test/README.md for more details.
You can also run tests or benchmarks directly for example:
$ cabal test --disable-optimization --flags -opt --test-show-details=streaming --test-option=--color streamly-tests
To view haddock docs open the link printed at the end of the haddock command, in your browser.
Nix users: There is a default.nix available which can be used to start
a nix-shell and then use the above commands as usual. nix-shell started
by default.nix creates a .cabal.nix for cabal configuration and sets
CABAL_DIR environment variable to point to that. Therefore, ~/.cabal
would not be used.
If the feature makes significant changes to design, we encourage you to open an issue as early as possible so that you do not have to redo much work because of changes in design decisions. However, if you are confident, you can still go ahead and take that risk as the maintainers are supposed to be reasonable people.
Please feel free to send a pull request (PR) whether it is a single letter typo fix or a complex change. We will accept any PR that makes a net positive change to the package. We encourage you to provide a complete, consistent change with test, documentation and benchmarks. You can contact the maintainers for any help or collaboration needed in that regard. However, if due to lack of time you are not able to complete the PR, you are still welcome to submit it, maintainers will try their best to actively contribute and pick up your change as long as the change is approved.
Here is a quick checklist for a PR, for details please see the next section:
- PR contains one logical changeset
- Each commit in the PR consists of a logical change
- Commits are rebased/squashed/fixup/reordered as needed
- Stylistic changes to irrelevant parts of the code are separated in independent commits.
- Code is formatted as per the style of the file or that of other files
- Compiler warnings are fixed
- Reasonable hlint suggestions are accepted
- Tests are added to cover the changed parts
- All tests pass
- Performance benchmarks are added, where applicable
- No significant regressions are reported by performance benchmarks
- Haddock documentation is added to user visible APIs and data types
- Docs are updated if necessary.
- Changelog is updated if needed
- The code conforms to the license, it is not stolen, credit is given, copyright notices are retained, original license is included if needed.
Lean PR: Please keep the reviewer in mind when sending pull requests. Use one PR for each logical changeset. A lean and thin PR with one independent logical change is more likely to be reviewed and merged quickly than a big monolithic PR with several unrelated changes.
PR Dependencies: If your change depends on an earlier PR you can create a branch from the old PR's branch, and raise a new PR targeting to merge into the old PR branch. Do not push the commits to the same PR just because the commit depends on that PR.
Commits: You are encouraged to group a logically related set of changes into a single commit. When the overall changeset is largish you can divide it into multiple smaller commits, with each commit having a logically grouped changeset and the title summarizing the logical grouping. Always keep in mind a logical division helps reviewers understand and review your code quickly, easier history tracking and when required clean reversal changes.
Functional Changes: Keep the reviewer in mind when making changes. Please resist the temptation to make style related changes to surrounding code unless you are changing that code anyway . Whenever possible, try to separate unrelated refactoring changes which do not affect functionality in separate commits so that it is easier for the reviewer to verify functional changes.
Style Changes: Make sure that your IDE/Editor is not automatically making sweeping style changes to all the files you are editing. That makes separating the signal from the noise very difficult and makes everything harder. If you would like to make style related changes then please send a separate PR with just those changes and no other functionality changes.
Rebasing: If your commits reflect how you fixed intermediate
problems during testing or made random changes at different times you
may have to squash your changes (git rebase -i) into a single commit
or logically related set of commits.
If during the course of development or before you send the PR you find that
your changes are conflicting with the master branch then use git rebase master to rebase your changes on top of master. DO NOT MERGE MASTER INTO YOUR
BRANCH.
It is a good idea to include tests for the changes where applicable. See the existing tests in the test directory. Also see the test/README.md for more details on how to run the tests.
For user visible APIs, it is a good idea to provide haddock documentation that is easily understood by the end programmer and does not sound highfalutin, and preferably with examples. If your change affects the tutorial or needs to be mentioned in the tutorial then please update the tutorial. Check if the additional guides are affected or need to updated.
It is a good idea to run performance benchmarks to see if your change affects any of the existing performance benchmarks. If you introduced something new then you may want to add benchmarks to check if it performs as well as expected by the programmers to deem it usable.
See the README file in the benchmark directory for more
details on how to run the benchmarks.
The first level of check is the regression in "allocations", this is the most stable measure of regression. "bytesCopied" is another stable measure, it gives an idea of the amount of long lived data being copied across generations of GC.
The next measure to look at is "cpuTime" this may have some variance from run to run because of factors like cpu frequency scaling, load on the system or the number of context switches etc. However, the variance would usually be within 5-10%, anything more than that is likely to be a red flag.
Quite often an increase in "cpuTime" would correspond to an increase in "allocations". Increase in "allocations" indicates an inefficiency in computing due to too much GC activity e.g. due to lack of fusion. However, it is also possible for the cpu time to go up without the allocations going up, this indicates an inefficiency in processing in general or more CPU being used for the same task. It could be because of inefficient code generation, branch mis-predictions or lack of cache locality etc.
For concurrent benchmarks we can compare "cpuTime" and "time" to check the degree of concurrency and total efficiency.
Any new changes that affect the user of the library in some way must be
documented under Unreleased section at the top of the Changelog. The
changes in the changelog must be organized in the following categories, in that
order:
- Breaking Changes
- Enhancements
- Bug Fixes
- Deprecations
If there are very few changes then you can just prefix a bullet with these annotations. If there are many changes make sections to group them. A section can be absent if there is nothing to add in it.
If you make changes that are incompatible with the released versions
of the library please indicate that in the Changelog as Breaking Changes
and also write short notes regarding what the programmers need to do to adapt
their existing code to the new change.
If you have copied code from elsewhere you need to conform to the licensing terms of the original code. Usually you would need to add a copyright notice in the source header, and include the license of the original code as per the terms of the license. If the code you are copying does not have an associated license please do not use it.
- Use https://streamly.composewell.com/ for searching in reference docs
- Build haddock docs for latest reference docs
- See the dev directory for design guidelines and dev documents.
Please see the Haskell coding style guide.
Ordering of variables in forall may be important in type applications. In
streams, we usually declare them in this order t m a.
Use the same order in constraints as well
Example,
func :: forall m a. (MonadIO m, Storable a) => ...
Some conventions that we follow in the StreamD code are illustrated by the following example:
mapM f (Stream step1 state1) = Stream step state
where
step gst st = do
r <- step1 (adaptState gst) st
case r of
Yield x s -> f x >>= \a -> return $ Yield a s
Skip s -> return $ Skip s
Stop -> return Stop
- For the input streams use numbering for
stepandstatee.g. step1/state1. For the output stream usestepandstate. - For state argument of
step, usest. - For result of executing a
stepuserorres - For the yielded element use
x - For the yielded state use
s
In general, the rule is - the shorter the scope of a variable the shorter its
name can be. For example, s has the shortest scope in the above code, st
has a bigger scope and state has the biggest scope.