descriptive
=====
Self-describing consumers/parsers
[Documentation](http://chrisdone.github.io/descriptive/)
There are a variety of Haskell libraries which are implementable
through a common interface: self-describing parsers:
* A formlet is a self-describing parser.
* A regular old text parser can be self-describing.
* A command-line options parser is a self-describing parser.
* A MUD command set is a self-describing parser.
* A JSON API can be a self-describing parser.
Consumption is done in this data type:
``` haskell
data Consumer s d a
```
### Making descriptive consumers
To make a consumer, this combinator is used:
``` haskell
consumer :: (StateT s m (Description d))
-- ^ Produce description based on the state.
-> (StateT s m (Result (Description d) a))
-- ^ Parse the state and maybe transform it if desired.
-> Consumer s d m a
```
The first argument generates a description based on some state. The
state is determined by whatever use-case you have. The second argument
parses from the state, which could be a stream of bytes, a list of
strings, a Map, a Vector, etc. You may or may not decide to modify the
state during generation of the description and during parsing.
### Running descriptive consumers
To use a consumer or describe what it does, these are used:
``` haskell
consume :: Consumer s d Identity a -- ^ The consumer to run.
-> s -- ^ Initial state.
-> Result (Description d) a
describe :: Consumer s d Identity a -- ^ The consumer to run.
-> s -- ^ Initial state. Can be \"empty\" if you don't use it for
-- generating descriptions.
-> Description d -- ^ A description and resultant state.
```
Alternatively the parser/printer can be run in a monad of your choice:
``` haskell
runConsumer :: Monad m
=> Consumer s d m a -- ^ The consumer to run.
-> StateT s m (Result (Description d) a)
runDescription :: Monad m
=> Consumer s d m a -- ^ The consumer to run.
-> StateT s m (Description d) -- ^ A description and resultant state.
```
### Descriptions
A description is like this:
``` haskell
data Description a
= Unit !a
| Bounded !Integer !Bound !(Description a)
| And !(Description a) !(Description a)
| Or !(Description a) !(Description a)
| Sequence ![Description a]
| Wrap a !(Description a)
| None
```
You configure the `a` for your use-case, but the rest is generatable
by the library. Afterwards, you can make your own pretty printing
function, which may be to generate an HTML form, to generate a
commandline `--help` screen, a man page, API docs for your JSON
parser, a text parsing grammar, etc. For example:
``` haskell
describeParser :: Description Text -> Text
describeForm :: Description (Html ()) -> Html ()
describeArgs :: Description CmdArgs -> Text
```
### Wrapping
One can wrap up a consumer to alter either the description or the
parser or both, this can be used for wrapping labels, or adding
validation, things of that nature:
``` haskell
wrap :: (StateT t m (Description d) -> StateT s m (Description d))
-- ^ Transform the description.
-> (StateT t m (Description d) -> StateT t m (Result (Description d) a) -> StateT s m (Result (Description d) b))
-- ^ Transform the parser. Can re-run the parser as many times as desired.
-> Consumer t d m a
-> Consumer s d m b
```
There is also a handy function written in terms of `wrap` which will
validate a consumer.
``` haskell
validate :: Monad m
=> d -- ^ Description of what it expects.
-> (a -> StateT s m (Maybe b)) -- ^ Attempt to parse the value.
-> Consumer s d m a -- ^ Consumer to add validation to.
-> Consumer s d m b -- ^ A new validating consumer.
```
See below for some examples of this library.
## Parsing characters
See `Descriptive.Char`.
``` haskell
λ> describe (many (char 'k') <> string "abc") mempty
And (Bounded 0 UnlimitedBound (Unit "k"))
(Sequence [Unit "a",Unit "b",Unit "c",None])
λ> consume (many (char 'k') <> string "abc") "kkkabc"
(Succeeded "kkkabc")
λ> consume (many (char 'k') <> string "abc") "kkkab"
(Failed (Unit "a character"))
λ> consume (many (char 'k') <> string "abc") "kkkabj"
(Failed (Unit "c"))
```
## Validating forms with named inputs
See `Descriptive.Form`.
``` haskell
λ> describe ((,) <$> input "username" <*> input "password") mempty
And (Unit (Input "username")) (Unit (Input "password"))
λ> consume ((,) <$>
input "username" <*>
input "password")
(M.fromList [("username","chrisdone"),("password","god")])
Succeeded ("chrisdone","god")
```
Conditions on two inputs:
``` haskell
login =
validate "confirmed password (entered the same twice)"
(\(x,y) ->
if x == y
then Just y
else Nothing)
((,) <$>
input "password" <*>
input "password2") <|>
input "token"
```
``` haskell
λ> consume login (M.fromList [("password2","gob"),("password","gob")])
Succeeded "gob"
λ> consume login (M.fromList [("password2","gob"),("password","go")])
Continued (And (Wrap (Constraint "confirmed password (entered the same twice)")
(And (Unit (Input "password"))
(Unit (Input "password2"))))
(Unit (Input "token")))
λ> consume login (M.fromList [("password2","gob"),("password","go"),("token","woot")])
Succeeded "woot"
```
## Validating forms with auto-generated input indexes
See `Descriptive.Formlet`.
``` haskell
λ> describe ((,) <$> indexed <*> indexed)
(FormletState mempty 0)
And (Unit (Index 0)) (Unit (Index 1))
λ> consume ((,) <$> indexed <*> indexed)
(FormletState (M.fromList [(0,"chrisdone"),(1,"god")]) 0)
Succeeded ("chrisdone","god")
λ> consume ((,) <$> indexed <*> indexed)
(FormletState (M.fromList [(0,"chrisdone")]) 0)
Failed (Unit (Index 1))
```
## Parsing command-line options
See `Descriptive.Options`.
``` haskell
server =
((,,,) <$>
constant "start" "cmd" () <*>
anyString "SERVER_NAME" <*>
switch "dev" "Enable dev mode?" <*>
arg "port" "Port to listen on")
((,,,) <$>
```
``` haskell
λ> describe server []
And (And (And (Unit (Constant "start"))
(Unit (AnyString "SERVER_NAME")))
(Unit (Flag "dev" "Enable dev mode?")))
(Unit (Arg "port" "Port to listen on"))
λ> consume server ["start","any","--port","1234","--dev"]
Succeeded ("start","any",True,"1234")
λ> consume server ["start","any","--port","1234"]
Succeeded ("start","any",False,"1234")
λ>
```
``` haskell
λ> textDescription (describe server [])
"start SERVER_NAME [--dev] --port <...>"
```
## Self-documenting JSON parser
See `Descriptive.JSON`.
``` haskell
-- | Submit a URL to reddit.
data Submission =
Submission {submissionToken :: !Integer
,submissionTitle :: !Text
,submissionComment :: !Text
,submissionSubreddit :: !Integer}
deriving (Show)
submission :: Monad m => Consumer Value Doc m Submission
submission =
object "Submission"
(Submission
<$> key "token" (integer "Submission token; see the API docs")
<*> key "title" (string "Submission title")
<*> key "comment" (string "Submission comment")
<*> key "subreddit" (integer "The ID of the subreddit"))
sample :: Value
sample =
toJSON (object
["token" .= 123
,"title" .= "Some title"
,"comment" .= "This is good"
,"subreddit" .= 234214])
badsample :: Value
badsample =
toJSON (object
["token" .= 123
,"title" .= "Some title"
,"comment" .= 123
,"subreddit" .= 234214])
```
``` haskell
λ> describe submission (toJSON ())
Wrap (Struct "Submission")
(And (And (And (Wrap (Key "token")
(Unit (Integer "Submission token; see the API docs")))
(Wrap (Key "title")
(Unit (Text "Submission title"))))
(Wrap (Key "comment")
(Unit (Text "Submission comment"))))
(Wrap (Key "subreddit")
(Unit (Integer "The ID of the subreddit"))))
λ> consume submission sample
Succeeded (Submission {submissionToken = 123
,submissionTitle = "Some title"
,submissionComment = "This is good"
,submissionSubreddit = 234214})
λ> consume submission badsample
Failed (Wrap (Struct "Submission")
(Wrap (Key "comment")
(Unit (Text "Submission comment"))))
```
The bad sample yields an informative message that:
* The error is in the Submission object.
* The key "comment".
* The type of that key should be a String and it should be a
Submission comment (or whatever invariants you'd like to mention).
## Parsing Attempto Controlled English for MUD commands
TBA. Will use
[this package](http://chrisdone.com/posts/attempto-controlled-english).
With ACE you can parse into:
``` haskell
parsed complV "<distrans-verb> a <noun> <prep> a <noun>" ==
Succeeded (ComplVDisV (DistransitiveV "<distrans-verb>")
(ComplNP (NPCoordUnmarked (UnmarkedNPCoord anoun Nothing)))
(ComplPP (PP (Preposition "<prep>")
(NPCoordUnmarked (UnmarkedNPCoord anoun Nothing)))))
```
Which I can then further parse with `descriptive` to yield
descriptions like:
<verb-phrase> [<noun-phrase> ..]
Or similar. Which would be handy for a MUD so that a user can write:
> Put the sword on the table.
## Producing questions and consuming the answers in Haskell
TBA. Will be a generalization of
[this type](https://github.com/chrisdone/exercise/blob/master/src/Exercise/Types.hs#L20).
It is a library which I am working on in parallel which will ask the
user questions and then validate the answers. Current output is like
this:
``` haskell
λ> describe (greaterThan 4 (integerExpr (parse id expr exercise)))
an integer greater than 4
λ> eval (greaterThan 4 (integerExpr (parse id expr exercise))) $(someHaskell "x = 1")
Left expected an expression, but got a declaration
λ> eval (greaterThan 4 (integerExpr (parse id expr exercise))) $(someHaskell "x")
Left expected an integer, but got an expression
λ> eval (greaterThan 4 (integerExpr (parse id expr exercise))) $(someHaskell "3")
Left expected an integer greater than 4
λ> eval (greaterThan 4 (integerExpr (parse id expr exercise))) $(someHaskell "5")
Right 5
```
This is also couples description with validation, but I will probably
rewrite it with this `descriptive` library.