LambdaCat Style Guide
=====================
This style guide is based on Johan Tibell's Haskell Style Guide at
<https://github.com/tibbe/haskell-style-guide/blob/master/haskell-style.md>.
This is a short document describing the preferred coding style for
this project. We've tried to cover the major areas of formatting and
naming. When something isn't covered by this guide you should stay
consistent with the code in the other modules.
Table of Contents
-----------------
1. Formatting
2. Imports
3. Comments
4. Naming
5. Misc
1. Formatting
-------------
### Line Length
Maximum line length is *78 characters*.
### Indentation
Tabs are illegal. Use spaces for indenting. Indent your code blocks
with *4 spaces*. Indent the `where` keyword two spaces to set it
apart from the rest of the code and indent the definitions in a
`where` clause 2 spaces. Some examples:
sayHello :: IO ()
sayHello = do
name <- getLine
putStrLn $ greeting name
where
greeting name = "Hello, " ++ name ++ "!"
filter :: (a -> Bool) -> [a] -> [a]
filter _ [] = []
filter p (x:xs)
| p x = x : filter p xs
| otherwise = filter p xs
### Blank Lines
One blank line between top-level definitions. No blank lines between
type signatures and function definitions. Add one blank line between
functions in a type class instance declaration if the functions bodies
are large. Use your judgement.
### Whitespace
Surround binary operators with a single space on either side. Don't
insert a space after a lambda.
### Data Declarations
Align the constructors in a data type definition. Indent deriving
declarations with two spaces. Example:
data Tree a = Branch a (Tree a) (Tree a)
| Leaf
deriving (Eq, Show)
For long type names the following formatting is also acceptable:
data HttpException
= InvalidStatusCode Int
| MissingContentHeader
deriving (Eq, Show)
Format records as follows:
data Person = Person
{ firstName :: String -- ^ First name
, lastName :: String -- ^ Last name
, age :: Int -- ^ Age
}
deriving (Eq, Show)
### List Declarations
Align the elements in the list. Example:
exceptions =
[ InvalidStatusCode
, MissingContentHeader
, InternalServerError
]
Optionally, you can skip the first newline. Use your judgement.
directions = [ North
, East
, South
, West
]
### Pragmas
For language extensions use the LANGUAGE pragma. Keep the
extensions in alphabetical order. Align the extensions. Indent
the closing bracket with two spaces. Example:
{-# LANGUAGE ExistentialQuantification
, FunctionalDependencies
, MultiParamTypeClasses
#-}
If you only have one extension put the closing bracket on the
same line:
{-# LANGUAGE ExistentialQuantification #-}
If you need to specify compiler options per file (e.g. you need
to disable certain warnings) align the options and keep them in
alphabetical order if reasonable. Example:
{-# OPTIONS_GHC -fno-warn-orphans
-fno-warn-unused-binds
#-}
Again if there is only one option put the closing bracket on the
same line.
Put pragmas immediately following the function they apply to.
Example:
id :: a -> a
id x = x
{-# INLINE id #-}
In the case of data type definitions you must put the pragma before
the type it applies to. Example:
data Array e = Array
{-# UNPACK #-} !Int
!ByteArray
### Hanging Lambdas
You may or may not indent the code following a "hanging" lambda. Use
your judgement. Some examples:
bar :: IO ()
bar = forM_ [1, 2, 3] $ \n -> do
putStrLn "Here comes a number!"
print n
foo :: IO ()
foo = alloca 10 $ \a ->
alloca 20 $ \b ->
cFunction a b
### Export Lists
Format export lists as follows:
module Data.Set
(
-- * The @Set@ type
Set
, empty
, singleton
-- * Querying
, member
)
where
2. Imports
----------
Imports should be grouped in the following order:
1. standard library imports
2. related third party imports
3. local application/library specific imports
Put a blank line between each group of imports. The imports in each
group should be sorted alphabetically, by module name.
It is recommended to use explicit import lists or `qualified` imports
for standard and third party libraries. This makes the code more
robust against changes in these libraries. Exception: The Prelude.
Use your judgement.
Format the imports as follows:
import Prelude hiding
( lookup
, null
)
import qualified Data.Map as Map
import Data.Maybe
( fromJust
)
import GHC.Exts ()
3. Comments
-----------
### Punctuation
Write proper sentences; start with a capital letter and use proper
punctuation.
### Top-Level Definitions
Comment every top level function (particularly exported functions),
and provide a type signature; use Haddock syntax in the comments.
Comment every exported data type. Some examples:
-- | Send a message on a socket. The socket must be in a connected
-- state. Returns the number of bytes sent. Applications are
-- responsible for ensuring that all data has been sent.
send :: Socket -- ^ Connected socket
-> ByteString -- ^ Data to send
-> IO Int -- ^ Bytes sent
-- | Bla bla bla.
data Person = Person
{ age :: Int -- ^ Age
, name :: String -- ^ First name
}
For functions the documentation should give enough information to
apply the function without looking at the function's definition.
### End-of-Line Comments
Separate end-of-line comments from the code using 2 spaces. Align
comments for data type definitions. Some examples:
data Parser = Parser
Int -- Current position
ByteString -- Remaining input
foo :: Int -> Int
foo n = salt * 32 + 9
where
salt = 453645243 -- Magic hash salt.
### Links
Use in-line links economically. You are encouraged to add links for
API names. It is not necessary to add links for all API names in a
Haddock comment. We therefore recommend adding a link to an API name
if:
* The user might actually want to click on it for more information (in
your judgment), and
* Only for the first occurrence of each API name in the comment (don't
bother repeating a link)
4. Naming
---------
For readability reasons, don't capitalize all letters when using an
abbreviation. For example, write `HttpServer` instead of
`HTTPServer`. Exception: Two letter abbreviations, e.g. `IO`.
5. Misc
-------
### Warnings ###
Code should be compilable with `-Wall -Werror`. There should be no
warnings.