| name | new-module |
| description | Scaffold a new Haskell module in mtg-pure that conforms to the strict house style (Safe header, HLINT-ignore block, mandatory export list, `import safe`, GADT-syntax data decls, InstanceSigs). Use when adding any new .hs module under src/, or when an existing module's header/imports need to be brought in line with the project conventions. |
New module in mtg-pure
The project builds with -Wall -Werror -Wmissing-export-lists and treats the
header shape as house style. A new module that doesn't follow this won't compile
or won't blend in. Full rationale is in
CODING_STYLE.md; this is the actionable recipe.
Do not run the build to check — see memory mtg-pure-no-builds. Match the
conventions by hand and let the user compile.
Header template
{-# LANGUAGE Safe #-}
{-# OPTIONS_GHC -Wno-unrecognised-pragmas #-}
{-# HLINT ignore "Avoid lambda" #-}
{-# HLINT ignore "Use const" #-}
{-# HLINT ignore "Use if" #-}
module MtgPure.Model.Foo (
Foo (..),
HasFoo (..),
) where
Order is fixed:
{-# LANGUAGE Safe #-} first — mandatory for model/engine modules. Only
UI/interop modules that must touch unsafe libraries use {-# LANGUAGE Unsafe #-}
or omit it.{-# OPTIONS_GHC -Wno-unrecognised-pragmas #-} so the HLINT pragmas below
don't trip -Werror.- Alphabetized block of
{-# HLINT ignore ... #-} — copy the subset that
applies from a neighboring module. This codebase keeps explicit lambdas and
case/if; the pragmas suppress HLINT's point-free suggestions. Common set:
"Avoid lambda", "Avoid lambda using \infix`", "Use const", "Use if", "Use camelCase", "Replace case with fromMaybe", "Replace case with maybe", "Redundant pure"`.
- Any module-local
{-# LANGUAGE ... #-} (e.g. ExtendedDefaultRules) sits
next to Safe. Project-wide extensions are already on via the cabal
default-extensions — don't re-declare those per file.
- Explicit export list is mandatory. Use
(..) to export a type with all
its constructors/fields.
Imports
- Use
import safe (and import safe qualified) for every import to preserve
the Safe guarantee.
- Alphabetize; leading commas on multi-line explicit lists.
- Reuse the conventional qualified aliases:
M (Control.Monad / .Trans),
List, NonEmpty, Map (Data.Map.Strict), Set, Stream, Char, GHC
(GHC.TypeLits).
- Import orphan-instance modules for effect with an empty list:
import safe MtgPure.Engine.Orphans ().
Body conventions
-
GADT syntax for data declarations, even simple records; deriving (Typeable).
-
Underscore-prefixed, per-type record fields (foo_bar), so names never
collide across record types.
-
InstanceSigs: repeat the method signature inside every instance, e.g.
instance Show Foo where
show :: Foo -> String
show = show . unFoo
-
Prefer \case, explicit lambdas, and spelled-out case/if over point-free.
-
newtype accessors use the un prefix (unFoo). Fields are strict by
default (StrictData) — no manual !.
-
Unimplemented paths: undefined (not error "..."), ideally with a
-- TODO: [reason]. Truly-impossible states: an InternalLogicError
constructor (see Prompt.hs), not a
bare undefined.
-
Engine functions start with logCall 'funcName do ... (TemplateHaskellQuotes
name quoting).
Register the module
Add the module name to exposed-modules in
mtg-pure.cabal, keeping that list alphabetized. GHC
won't see the file otherwise. LoadAllModules.hs is generated
(via Script.GenerateLoadAllModules) — don't hand-edit it.
Checklist
