time

time is the Haskell library for clocks, calendars, time zones, local time, and formatting/parsing of time values. It is bundled with GHC and is also maintained as the time package on Hackage.

The package is configured with Cabal and uses a generated C header. When building directly from a git checkout, run autoreconf -i before the first Cabal configure/build step if configure or the autoconf files are missing or stale. The devcontainer build scripts do this for normal builds.

Repository Layout

• lib/: library modules exposed through Data.Time and internal modules.
• test/main/: main Tasty/QuickCheck/HUnit test suite.
• test/template/: Template Haskell test suite.
• test/unix/: Unix-specific tests.
• test/: small standalone test executables.
• benchmark/: Criterion benchmark executable.
• bin/: build helper scripts used by the devcontainer.
• .devcontainer/: full build environment with supported GHC targets.
• time.cabal: package metadata, module lists, test suites, and dependencies.
• cabal.project: local Cabal project file.
• justfile: convenience commands for the devcontainer workflow.

Common Commands

The primary workflow uses the devcontainer:

just shell
just format
just build
just haddock

just build runs bin/build-all in the devcontainer, which exercises the native, expired-native, WebAssembly, JavaScript, and MicroHs build paths configured there.

For focused local work, Cabal commands are useful when a suitable GHC and Cabal are on PATH:

autoreconf -i
cabal test test-main
cabal test test-main --test-options '-p /CalendarDiffTime/'
cabal repl
cabal haddock

If dependencies have not been fetched yet, run:

cabal update

Testing

The main test suite is test-main. Its entrypoint is test/main/Main.hs, and most reusable test support lives under test/main/Test.

Useful focused test patterns:

cabal test test-main --test-options '-p /CalendarDiffDays/'
cabal test test-main --test-options '-p /CalendarDiffTime/'
cabal test test-main --test-options '-p /ISO8601/'

When adding a new test module under test/main/Test, add it to the other-modules list for test-suite test-main in time.cabal.

Formatting And Style

The project uses fourmolu.yaml for formatting configuration. The devcontainer installs Fourmolu and exposes it through:

just format

The Cabal file enables -Wall and -fwarn-tabs; avoid tabs and keep warnings clean.

Supported Compilers

The Cabal metadata currently lists these supported GHC versions:

• GHC 9.8.4
• GHC 9.10.3
• GHC 9.12.4
• GHC 9.14.1

The devcontainer also includes older expired-native targets and cross targets used by the full build.

Links

• Homepage: https://github.com/haskell/time
• Issues: https://github.com/haskell/time/issues
• GHC: https://www.haskell.org/ghc/