root / src / Ganeti / BasicTypes.hs @ 4651c69f
History | View | Annotate | Download (7.8 kB)
1 |
{-# LANGUAGE FlexibleInstances #-} |
---|---|
2 |
|
3 |
{- |
4 |
|
5 |
Copyright (C) 2009, 2010, 2011, 2012 Google Inc. |
6 |
|
7 |
This program is free software; you can redistribute it and/or modify |
8 |
it under the terms of the GNU General Public License as published by |
9 |
the Free Software Foundation; either version 2 of the License, or |
10 |
(at your option) any later version. |
11 |
|
12 |
This program is distributed in the hope that it will be useful, but |
13 |
WITHOUT ANY WARRANTY; without even the implied warranty of |
14 |
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
15 |
General Public License for more details. |
16 |
|
17 |
You should have received a copy of the GNU General Public License |
18 |
along with this program; if not, write to the Free Software |
19 |
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
20 |
02110-1301, USA. |
21 |
|
22 |
-} |
23 |
|
24 |
module Ganeti.BasicTypes |
25 |
( GenericResult(..) |
26 |
, genericResult |
27 |
, Result |
28 |
, ResultT(..) |
29 |
, resultT |
30 |
, FromString(..) |
31 |
, isOk |
32 |
, isBad |
33 |
, eitherToResult |
34 |
, annotateResult |
35 |
, iterateOk |
36 |
, select |
37 |
, LookupResult(..) |
38 |
, MatchPriority(..) |
39 |
, lookupName |
40 |
, goodLookupResult |
41 |
, goodMatchPriority |
42 |
, prefixMatch |
43 |
, compareNameComponent |
44 |
, ListSet(..) |
45 |
, emptyListSet |
46 |
) where |
47 |
|
48 |
import Control.Applicative |
49 |
import Control.Monad |
50 |
import Control.Monad.Trans |
51 |
import Data.Function |
52 |
import Data.List |
53 |
import Data.Set (Set) |
54 |
import qualified Data.Set as Set (empty) |
55 |
import Text.JSON (JSON) |
56 |
import qualified Text.JSON as JSON (readJSON, showJSON) |
57 |
|
58 |
-- | Generic monad for our error handling mechanisms. |
59 |
data GenericResult a b |
60 |
= Bad a |
61 |
| Ok b |
62 |
deriving (Show, Eq) |
63 |
|
64 |
-- | Sum type structure of GenericResult. |
65 |
genericResult :: (a -> c) -> (b -> c) -> GenericResult a b -> c |
66 |
genericResult f _ (Bad a) = f a |
67 |
genericResult _ g (Ok b) = g b |
68 |
|
69 |
-- | Type alias for a string Result. |
70 |
type Result = GenericResult String |
71 |
|
72 |
-- | Type class for things that can be built from strings. |
73 |
class FromString a where |
74 |
mkFromString :: String -> a |
75 |
|
76 |
-- | Trivial 'String' instance; requires FlexibleInstances extension |
77 |
-- though. |
78 |
instance FromString [Char] where |
79 |
mkFromString = id |
80 |
|
81 |
-- | 'Monad' instance for 'GenericResult'. |
82 |
instance (FromString a) => Monad (GenericResult a) where |
83 |
(>>=) (Bad x) _ = Bad x |
84 |
(>>=) (Ok x) fn = fn x |
85 |
return = Ok |
86 |
fail = Bad . mkFromString |
87 |
|
88 |
instance Functor (GenericResult a) where |
89 |
fmap _ (Bad msg) = Bad msg |
90 |
fmap fn (Ok val) = Ok (fn val) |
91 |
|
92 |
instance MonadPlus (GenericResult String) where |
93 |
mzero = Bad "zero Result when used as MonadPlus" |
94 |
-- for mplus, when we 'add' two Bad values, we concatenate their |
95 |
-- error descriptions |
96 |
(Bad x) `mplus` (Bad y) = Bad (x ++ "; " ++ y) |
97 |
(Bad _) `mplus` x = x |
98 |
x@(Ok _) `mplus` _ = x |
99 |
|
100 |
instance Applicative (GenericResult a) where |
101 |
pure = Ok |
102 |
(Bad f) <*> _ = Bad f |
103 |
_ <*> (Bad x) = Bad x |
104 |
(Ok f) <*> (Ok x) = Ok $ f x |
105 |
|
106 |
-- | This is a monad transformation for Result. It's implementation is |
107 |
-- based on the implementations of MaybeT and ErrorT. |
108 |
newtype ResultT a m b = ResultT {runResultT :: m (GenericResult a b)} |
109 |
|
110 |
instance (Monad m, FromString a) => Monad (ResultT a m) where |
111 |
fail err = ResultT (return . Bad $ mkFromString err) |
112 |
return = lift . return |
113 |
x >>= f = ResultT $ do |
114 |
a <- runResultT x |
115 |
case a of |
116 |
Ok val -> runResultT $ f val |
117 |
Bad err -> return $ Bad err |
118 |
|
119 |
instance MonadTrans (ResultT a) where |
120 |
lift x = ResultT (liftM Ok x) |
121 |
|
122 |
instance (MonadIO m, FromString a) => MonadIO (ResultT a m) where |
123 |
liftIO = lift . liftIO |
124 |
|
125 |
-- | Lift a `Result` value to a `ResultT`. |
126 |
resultT :: Monad m => GenericResult a b -> ResultT a m b |
127 |
resultT = ResultT . return |
128 |
|
129 |
-- | Simple checker for whether a 'GenericResult' is OK. |
130 |
isOk :: GenericResult a b -> Bool |
131 |
isOk (Ok _) = True |
132 |
isOk _ = False |
133 |
|
134 |
-- | Simple checker for whether a 'GenericResult' is a failure. |
135 |
isBad :: GenericResult a b -> Bool |
136 |
isBad = not . isOk |
137 |
|
138 |
-- | Converter from Either to 'GenericResult'. |
139 |
eitherToResult :: Either a b -> GenericResult a b |
140 |
eitherToResult (Left s) = Bad s |
141 |
eitherToResult (Right v) = Ok v |
142 |
|
143 |
-- | Annotate a Result with an ownership information. |
144 |
annotateResult :: String -> Result a -> Result a |
145 |
annotateResult owner (Bad s) = Bad $ owner ++ ": " ++ s |
146 |
annotateResult _ v = v |
147 |
|
148 |
-- | Iterate while Ok. |
149 |
iterateOk :: (a -> GenericResult b a) -> a -> [a] |
150 |
iterateOk f a = genericResult (const []) ((:) a . iterateOk f) (f a) |
151 |
|
152 |
-- * Misc functionality |
153 |
|
154 |
-- | Return the first result with a True condition, or the default otherwise. |
155 |
select :: a -- ^ default result |
156 |
-> [(Bool, a)] -- ^ list of \"condition, result\" |
157 |
-> a -- ^ first result which has a True condition, or default |
158 |
select def = maybe def snd . find fst |
159 |
|
160 |
-- * Lookup of partial names functionality |
161 |
|
162 |
-- | The priority of a match in a lookup result. |
163 |
data MatchPriority = ExactMatch |
164 |
| MultipleMatch |
165 |
| PartialMatch |
166 |
| FailMatch |
167 |
deriving (Show, Enum, Eq, Ord) |
168 |
|
169 |
-- | The result of a name lookup in a list. |
170 |
data LookupResult = LookupResult |
171 |
{ lrMatchPriority :: MatchPriority -- ^ The result type |
172 |
-- | Matching value (for ExactMatch, PartialMatch), Lookup string otherwise |
173 |
, lrContent :: String |
174 |
} deriving (Show) |
175 |
|
176 |
-- | Lookup results have an absolute preference ordering. |
177 |
instance Eq LookupResult where |
178 |
(==) = (==) `on` lrMatchPriority |
179 |
|
180 |
instance Ord LookupResult where |
181 |
compare = compare `on` lrMatchPriority |
182 |
|
183 |
-- | Check for prefix matches in names. |
184 |
-- Implemented in Ganeti core utils.text.MatchNameComponent |
185 |
-- as the regexp r"^%s(\..*)?$" % re.escape(key) |
186 |
prefixMatch :: String -- ^ Lookup |
187 |
-> String -- ^ Full name |
188 |
-> Bool -- ^ Whether there is a prefix match |
189 |
prefixMatch = isPrefixOf . (++ ".") |
190 |
|
191 |
-- | Is the lookup priority a "good" one? |
192 |
goodMatchPriority :: MatchPriority -> Bool |
193 |
goodMatchPriority ExactMatch = True |
194 |
goodMatchPriority PartialMatch = True |
195 |
goodMatchPriority _ = False |
196 |
|
197 |
-- | Is the lookup result an actual match? |
198 |
goodLookupResult :: LookupResult -> Bool |
199 |
goodLookupResult = goodMatchPriority . lrMatchPriority |
200 |
|
201 |
-- | Compares a canonical name and a lookup string. |
202 |
compareNameComponent :: String -- ^ Canonical (target) name |
203 |
-> String -- ^ Partial (lookup) name |
204 |
-> LookupResult -- ^ Result of the lookup |
205 |
compareNameComponent cnl lkp = |
206 |
select (LookupResult FailMatch lkp) |
207 |
[ (cnl == lkp , LookupResult ExactMatch cnl) |
208 |
, (prefixMatch lkp cnl , LookupResult PartialMatch cnl) |
209 |
] |
210 |
|
211 |
-- | Lookup a string and choose the best result. |
212 |
chooseLookupResult :: String -- ^ Lookup key |
213 |
-> String -- ^ String to compare to the lookup key |
214 |
-> LookupResult -- ^ Previous result |
215 |
-> LookupResult -- ^ New result |
216 |
chooseLookupResult lkp cstr old = |
217 |
-- default: use class order to pick the minimum result |
218 |
select (min new old) |
219 |
-- special cases: |
220 |
-- short circuit if the new result is an exact match |
221 |
[ (lrMatchPriority new == ExactMatch, new) |
222 |
-- if both are partial matches generate a multiple match |
223 |
, (partial2, LookupResult MultipleMatch lkp) |
224 |
] where new = compareNameComponent cstr lkp |
225 |
partial2 = all ((PartialMatch==) . lrMatchPriority) [old, new] |
226 |
|
227 |
-- | Find the canonical name for a lookup string in a list of names. |
228 |
lookupName :: [String] -- ^ List of keys |
229 |
-> String -- ^ Lookup string |
230 |
-> LookupResult -- ^ Result of the lookup |
231 |
lookupName l s = foldr (chooseLookupResult s) |
232 |
(LookupResult FailMatch s) l |
233 |
|
234 |
-- | Wrapper for a Haskell 'Set' |
235 |
-- |
236 |
-- This type wraps a 'Set' and it is used in the Haskell to Python |
237 |
-- opcode generation to transform a Haskell 'Set' into a Python 'list' |
238 |
-- without duplicate elements. |
239 |
newtype ListSet a = ListSet { unListSet :: Set a } |
240 |
deriving (Eq, Show) |
241 |
|
242 |
instance (Ord a, JSON a) => JSON (ListSet a) where |
243 |
showJSON = JSON.showJSON . unListSet |
244 |
readJSON = liftM ListSet . JSON.readJSON |
245 |
|
246 |
emptyListSet :: ListSet a |
247 |
emptyListSet = ListSet Set.empty |