Haskell thrift codegen and runtime library, working in progress.
Following're some rules for IDL compiler:
- Haskell module name will be camelized and capitalized path/filename relative to
CWD, for example:
...
├── IDL
│ ├── rockstable.thrift
│ └── rockstable_master.thrift
...
If you run thrift-haskell-compiler -o data ./IDL, you will get your compiled files in:
├── Data
│ └── Idl
│ ├── Rockstable.hs
│ └── RockstableMaster.hs
├── IDL
│ ├── rockstable.thrift
│ └── rockstable_master.thrift
-
Identifier will be camelized (and capitalized if needed).
-
Type definitions will be compiled into
typedeclarations.
typedef list<Tweet> TweetList
will be compiled to:
type TweetList = [Tweet]
-
Senum and Slist are deprecated, thus unsupportted.
-
Enum is very straightforward, except that hex numeric literals are not supportted(which follows the thrift spec AFAICT).
enum TweetType {
TWEET,
RETWEET = 2,
DM = 0xa, // this field's behavior is undefined
REPLY
}
will compiled to:
data TweetType = Tweet
| Retweet
| Dm
| Reply
deriving (Eq, Ord, Show, Thrift.Data, Thrift.Typeable,
Thrift.Generic, Thrift.Hashable)
instance Enum TweetType where
fromEnum Tweet = 0
fromEnum Retweet = 2
fromEnum Dm = 4
fromEnum Reply = 5
toEnum 0 = Tweet
toEnum 2 = Retweet
toEnum 4 = Dm
toEnum 5 = Reply
instance Thrift.Thrift TweetType where
typeCode = Thrift.TypeCode Thrift.tcInt32
defaultValue = Tweet
toTValue Tweet = Thrift.TInt32 0
toTValue Retweet = Thrift.TInt32 2
toTValue Dm = Thrift.TInt32 4
toTValue Reply = Thrift.TInt32 5
fromTValue (Thrift.TInt32 0) = Tweet
fromTValue (Thrift.TInt32 2) = Retweet
fromTValue (Thrift.TInt32 4) = Dm
fromTValue (Thrift.TInt32 5) = Reply
fromTValue _ = error "bad enum value"- Struct field will be prepend with struct name to eliminate name collision, Every field must have a unique, positive integer identifier:
struct Tweet {
1: required i32 userId;
2: required string userName;
3: required string text;
4: optional Location loc;
5: optional TweetType tweetType = TweetType.TWEET;
16: optional string language = "english";
}
will compiled to:
data Tweet = Tweet{tweetUserId :: Thrift.Int32,
tweetUserName :: Thrift.Text, tweetText :: Thrift.Text,
tweetLoc :: Maybe Location, tweetTweetType :: Maybe TweetType,
tweetLanguage :: Maybe Thrift.Text}
deriving (Eq, Show, Thrift.Data, Thrift.Typeable, Thrift.Generic,
Thrift.Hashable)
instance Thrift.Thrift Tweet where
typeCode = Thrift.TypeCode Thrift.tcStruct
defaultValue
= let tweetUserId = Thrift.defaultValue
tweetUserName = Thrift.defaultValue
tweetText = Thrift.defaultValue
tweetLoc = Nothing
tweetTweetType = Just Tweet
tweetLanguage = Just "english"
in Tweet{..}
toTValue Tweet{..}
= Thrift.TStruct
(Thrift.catMaybes
[Just (1, Thrift.toTValue tweetUserId),
Just (2, Thrift.toTValue tweetUserName),
Just (3, Thrift.toTValue tweetText),
case tweetLoc of
Just x -> Just (4, Thrift.toTValue x)
_ -> Nothing,
case tweetTweetType of
Just x -> Just (5, Thrift.toTValue x)
_ -> Nothing,
case tweetLanguage of
Just x -> Just (16, Thrift.toTValue x)
_ -> Nothing])
fromTValue (Thrift.TStruct x)
= let m = Thrift.fromList x
tweetUserId = Thrift.lookupRequired (fromIntegral 1) m
tweetUserName = Thrift.lookupRequired (fromIntegral 2) m
tweetText = Thrift.lookupRequired (fromIntegral 3) m
tweetLoc = Thrift.lookupOptional Nothing (fromIntegral 4) m
tweetTweetType
= Thrift.lookupOptional (Just Tweet) (fromIntegral 5) m
tweetLanguage
= Thrift.lookupOptional (Just "english") (fromIntegral 16) m
in Tweet{..}
fromTValue _ = error "bad struct value"Please notice that there exists a so called default field type, it's treated like required field in data declarations, eg. without Maybe. Because haskell really don't have a undefined/nil notation, every field must be present as long as it is not optional. During deserialization, if peer doesn't send a default field, a defaultValue will be used, for basic types those are:
bool: false
i8, i16, i32, i64, double : 0
string: ""
binary: ""
MapType: []
SetType: []
ListType: []
This may seemed arbitrary, but you will set these default field anyway so the choice of defaults are not important here, and you can supply a default value using thift's syntax. Following is a table describe every possible scenario:
| field requireness | data type | serialize | deserialize | deserialize when user supply a default value x |
|---|---|---|---|---|
| required | a | always | must present, otherwise error | ignore user supply value x |
| optional | Maybe a | if Just | not present == Nothing | not present == Just x |
| default(function return) | a | always | not present == Thrift.def | not present == x |
The term present here means a field can be find by its identifier AND the type conversion is successful, if a field with same identifier but different type exists, we will simply call error. Note we won't do any implicit conversion, that means a Int32 field x is NOT present even there is an IntX field x.
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