| Copyright | (c) 2000 Andy Gill, (c) 2010 University of Kansas, (c) 2013-2015 Maarten Faddegon |
|---|---|
| License | BSD3 |
| Maintainer | hoed@maartenfaddegon.nl |
| Stability | experimental |
| Portability | POSIX |
| Safe Haskell | None |
| Language | Haskell2010 |
Debug.Hoed.Pure
Contents
Description
Hoed is a tracer and debugger for the programming language Haskell.
Hoed.Pure is recommended over Hoed.Stk: in contrast to Hoed.Stk you can optimize your program and do not need to enable profiling when using Hoed.Pure.
To locate a defect with Hoed.Pure you annotate suspected functions and compile as usual. Then you run your program, information about the annotated functions is collected. Finally you connect to a debugging session using a webbrowser.
Let us consider the following program, a defective implementation of a parity function with a test property.
import Test.QuickCheck isOdd :: Int -> Bool isOdd n = isEven (plusOne n) isEven :: Int -> Bool isEven n = mod2 n == 0 plusOne :: Int -> Int plusOne n = n + 1 mod2 :: Int -> Int mod2 n = div n 2 prop_isOdd :: Int -> Bool prop_isOdd x = isOdd (2*x+1) main :: IO () main = printO (prop_isOdd 1) main :: IO () main = quickcheck prop_isOdd
Using the property-based test tool QuickCheck we find the counter example `1` for our property.
./MyProgram *** Failed! Falsifiable (after 1 test): 1
Hoed can help us determine which function is defective. We annotate the functions isOdd, isEven, plusOne and mod2 as follows:
import Debug.Hoed.Pure isOdd :: Int -> Bool isOdd = observe "isOdd" isOdd' isOdd' n = isEven (plusOne n) isEven :: Int -> Bool isEven = observe "isEven" isEven' isEven' n = mod2 n == 0 plusOne :: Int -> Int plusOne = observe "plusOne" plusOne' plusOne' n = n + 1 mod2 :: Int -> Int mod2 = observe "mod2" mod2' mod2' n = div n 2 prop_isOdd :: Int -> Bool prop_isOdd x = isOdd (2*x+1) main :: IO () main = printO (prop_isOdd 1)
After running the program a computation tree is constructed and displayed in a web browser.
./MyProgram False Listening on http://127.0.0.1:10000/
After running the program a computation tree is constructed and displayed in a
web browser. You can freely browse this tree to get a better understanding of
your program. If your program misbehaves, you can judge the computation
statements in the tree as right or wrong according to your intention. When
enough statements are judged the debugger tells you the location of the fault
in your code.
Read more about Hoed on its project homepage https://wiki.haskell.org/Hoed.
Papers on the theory behind Hoed can be obtained via http://maartenfaddegon.nl/#pub.
I am keen to hear about your experience with Hoed: where did you find it useful and where would you like to see improvement? You can send me an e-mail at hoed@maartenfaddegon.nl, or use the github issue tracker https://github.com/MaartenFaddegon/hoed/issues.
- observe :: Observable a => String -> a -> a
- runO :: IO a -> IO ()
- testO :: Show a => (a -> Bool) -> a -> IO ()
- printO :: Show a => a -> IO ()
- logO :: FilePath -> IO a -> IO ()
- runOwp :: [Propositions] -> IO a -> IO ()
- testOwp :: Show a => [Propositions] -> (a -> Bool) -> a -> IO ()
- logOwp :: PropVarGen String -> FilePath -> [Propositions] -> IO a -> IO ()
- data Propositions = Propositions {
- propositions :: [Proposition]
- propType :: PropType
- funName :: String
- extraModules :: [Module]
- data PropType
- type Proposition = (PropositionType, Module, String, [Int])
- data PropositionType
- data Module = Module {
- moduleName :: String
- searchPath :: String
- propVarError :: PropVarGen String
- propVarFresh :: PropVarGen String
- traceOnly :: IO a -> IO ()
- observeTempl :: String -> Q Exp
- observedTypes :: String -> [Q Type] -> Q [Dec]
- observeCC :: Observable a => String -> a -> a
- class ParEq a where
- newtype Observer = O (forall a. Observable a => String -> a -> a)
- class Observable a where
- observer :: a -> Parent -> a
- (<<) :: Observable a => ObserverM (a -> b) -> a -> ObserverM b
- thunk :: (a -> Parent -> a) -> a -> ObserverM a
- nothunk :: a -> ObserverM a
- send :: String -> ObserverM a -> Parent -> a
- observeBase :: Show a => a -> Parent -> a
- observeOpaque :: String -> a -> Parent -> a
- debugO :: IO a -> IO Trace
- data CDS
- class Generic a
Basic annotations
observe :: Observable a => String -> a -> a Source
Functions which you suspect of misbehaving are annotated with observe and should have a cost centre set. The name of the function, the label of the cost centre and the label given to observe need to be the same.
Consider the following function:
triple x = x + x
This function is annotated as follows:
triple y = (observe "triple" (\x -> {# SCC "triple" #} x + x)) yTo produce computation statements like:
triple 3 = 6
To observe a value its type needs to be of class Observable. We provided instances for many types already. If you have defined your own type, and want to observe a function that takes a value of this type as argument or returns a value of this type, an Observable instance can be derived as follows:
data MyType = MyNumber Int | MyName String deriving Generic instance Observable MyType
The main entry point; run some IO code, and debug inside it.
After the IO action is completed, an algorithmic debugging session is started at
http://localhost:10000/ to which you can connect with your webbrowser.
For example:
main = runO $ do print (triple 3)
print (triple 2)
logO :: FilePath -> IO a -> IO () Source
Trace and write computation tree to file. Useful for regression testing.
Property-based judging
runOwp :: [Propositions] -> IO a -> IO () Source
Use property based judging.
testOwp :: Show a => [Propositions] -> (a -> Bool) -> a -> IO () Source
Repeat and trace a failing testcase
logOwp :: PropVarGen String -> FilePath -> [Propositions] -> IO a -> IO () Source
As logO, but with property-based judging.
data Propositions Source
Constructors
| Propositions | |
Fields
| |
type Proposition = (PropositionType, Module, String, [Int]) Source
Constructors
| Module | |
Fields
| |
propVarError :: PropVarGen String Source
propVarFresh :: PropVarGen String Source
Experimental annotations
observeTempl :: String -> Q Exp Source
observeCC :: Observable a => String -> a -> a Source
Parallel equality
Minimal complete definition
Nothing
The Observable class
Constructors
| O (forall a. Observable a => String -> a -> a) |
class Observable a where Source
Minimal complete definition
Nothing
Instances
| Observable Bool Source | |
| Observable Char Source | |
| Observable Double Source | |
| Observable Float Source | |
| Observable Int Source | |
| Observable Integer Source | |
| Observable () Source | |
| Observable Dynamic Source | |
| Observable SomeException Source | |
| Observable a => Observable [a] Source | |
| Observable a => Observable (IO a) Source | |
| Observable a => Observable (Maybe a) Source | |
| (Observable a, Observable b) => Observable (a -> b) Source | |
| (Observable a, Observable b) => Observable (Either a b) Source | |
| (Observable a, Observable b) => Observable (a, b) Source | |
| (Ix a, Observable a, Observable b) => Observable (Array a b) Source | |
| (Observable a, Observable b, Observable c) => Observable (a, b, c) Source | |
| (Observable a, Observable b, Observable c, Observable d) => Observable (a, b, c, d) Source | |
| (Observable a, Observable b, Observable c, Observable d, Observable e) => Observable (a, b, c, d, e) Source |
(<<) :: Observable a => ObserverM (a -> b) -> a -> ObserverM b infixl 9 Source
observeBase :: Show a => a -> Parent -> a Source
observeOpaque :: String -> a -> Parent -> a Source
class Generic a
Representable types of kind *. This class is derivable in GHC with the DeriveGeneric flag on.
Instances