1 files changed, 56 insertions, 0 deletions
diff --git a/pre_commit/languages/haskell.py b/pre_commit/languages/haskell.py
new file mode 100644
index 0000000..76442eb
--- /dev/null
+++ b/pre_commit/languages/haskell.py
@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+import contextlib
+import os.path
+from typing import Generator
+from typing import Sequence
+
+from pre_commit import lang_base
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import PatchesT
+from pre_commit.envcontext import Var
+from pre_commit.errors import FatalError
+from pre_commit.prefix import Prefix
+
+ENVIRONMENT_DIR = 'hs_env'
+get_default_version = lang_base.basic_get_default_version
+health_check = lang_base.basic_health_check
+run_hook = lang_base.basic_run_hook
+
+
+def get_env_patch(target_dir: str) -> PatchesT:
+    bin_path = os.path.join(target_dir, 'bin')
+    return (('PATH', (bin_path, os.pathsep, Var('PATH'))),)
+
+
+@contextlib.contextmanager
+def in_env(prefix: Prefix, version: str) -> Generator[None, None, None]:
+    envdir = lang_base.environment_dir(prefix, ENVIRONMENT_DIR, version)
+    with envcontext(get_env_patch(envdir)):
+        yield
+
+
+def install_environment(
+    prefix: Prefix,
+    version: str,
+    additional_dependencies: Sequence[str],
+) -> None:
+    lang_base.assert_version_default('haskell', version)
+    envdir = lang_base.environment_dir(prefix, ENVIRONMENT_DIR, version)
+
+    pkgs = [*prefix.star('.cabal'), *additional_dependencies]
+    if not pkgs:
+        raise FatalError('Expected .cabal files or additional_dependencies')
+
+    bindir = os.path.join(envdir, 'bin')
+    os.makedirs(bindir, exist_ok=True)
+    lang_base.setup_cmd(prefix, ('cabal', 'update'))
+    lang_base.setup_cmd(
+        prefix,
+        (
+            'cabal', 'install',
+            '--install-method', 'copy',
+            '--installdir', bindir,
+            *pkgs,
+        ),
+    )