DDevelopment & Design

Easy Hoogle usage from bash

What is hoogle?

Hoogle is Google for searching of Haskell functions. You could ask it for function name or its signature. There is available command hoogle, which could be installed using stack:
$ stack install hoogle

Using hoogle from command line {#using-hoogle-from-command-line} To

hoogle a function you could just pass it as parameter:
$ hoogle fmap
Prelude fmap :: Functor f => (a -> b) -> f a -> f b
Data.Functor fmap :: Functor f => (a -> b) -> f a -> f b
Control.Monad fmap :: Functor f => (a -> b) -> f a -> f b
Control.Monad.Instances fmap :: Functor f => (a -> b) -> f a -> f b
Data.Traversable fmapDefault :: Traversable t => (a -> b) -> t a -> t b
Network.Stream fmapE :: (a -> Result b) -> IO (Result a) -> IO (Result b) or pass its signature:

$ hoogle "(a -> b -> c) -> [a] -> [b] -> [c]"
Prelude zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
Data.List zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
Control.Applicative liftA2 :: Applicative f => (a -> b -> c) -> f a -> f b -> f c
Control.Monad liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
Prelude scanl :: (a -> b -> a) -> a -> [b] -> [a]
Data.List scanl :: (a -> b -> a) -> a -> [b] -> [a]
Prelude scanr :: (a -> b -> b) -> b -> [a] -> [b]
Data.List scanr :: (a -> b -> b) -> b -> [a] -> [b]
Data.List deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
Data.List intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
... But it shows only list of the signatures of the functions. Sometimes we want to see more information about function. If you use option

-i, then additional information will be shown:
$ hoogle -i “(a -> b -> c) -> [a] -> [b] -> [c]”
Prelude zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] 

zipWith generalises zip by zipping with the function given as the first argument, instead of a tupling function. For example, zipWith (+) is applied to two lists to produce the list of corresponding sums.

From package base
zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] And again it is not enough, because it shows only documentation of first function from the list. We have to move a counter to see documentation of further functions, e. g. to show information about third item from the list: 

$ hoogle -i -s 3 "(a -> b -> c) -> [a] -> [b] -> [c]"
Control.Applicative liftA2 :: Applicative f => (a -> b -> c) -> f a -> f b -> f c

Lift a binary function to actions.

From package base
liftA2 :: Applicative f => (a -> b -> c) -> f a -> f b -> f c

Easier hoogle usage in bash {#easier-hoogle-usage-in-bash} It is cumbersome to count each time you want to read info about further functions, so I have prepared bash function which makes it easier. To search for function type:

$ hoog "(a->b) -> f a -> f b"
1) Data.Traversable fmapDefault :: Traversable t => (a -> b) -> t a -> t b
2) Prelude fmap :: Functor f => (a -> b) -> f a -> f b
3) Data.Functor fmap :: Functor f => (a -> b) -> f a -> f b
4) Control.Monad fmap :: Functor f => (a -> b) -> f a -> f b
5) Control.Monad.Instances fmap :: Functor f => (a -> b) -> f a -> f b
6) Data.Functor (<$>) :: Functor f => (a -> b) -> f a -> f b
7) Control.Applicative (<$>) :: Functor f => (a -> b) -> f a -> f b Each function will have its counter at the beginning and just add its number at the end of command to show more information about specific function: 

$ hoog "(a->b) -> f a -> f b" 6
Searching for: (a -> b) -> f a -> f b
Data.Functor (<$>) :: Functor f => (a -> b) -> f a -> f b

An infix synonym for fmap.

From package base
(<$>) :: Functor f => (a -> b) -> f a -> f b

How to install hoog command? {#how-to-install-hoog-command} Command is available

here. To use this command just add it to your ~/bashrc file.

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DDevelopment & Design

Thought static method can’t be easy to mock, stub nor track? Wrong!

No matter why, no matter is it a good idea. Sometimes one just wants to check or it's necessary to be done. Mock a static method, woot? Impossibru!

In pure Java world it is still a struggle. But Groovy allows you to do that really simple. Well, not groovy alone, but with a great support of Spock.

Lets move on straight to the example. To catch some context we have an abstract for the example needs. A marketing project with a set of offers. One to many.

import spock.lang.Specification

class OfferFacadeSpec extends Specification {

    OfferFacade facade = new OfferFacade()

    def setup() {
        GroovyMock(Project, global: true)
    }

    def 'delegates an add offer call to the domain with proper params'() {
        given:
            Map params = [projId: projectId, name: offerName]

        when:
            Offer returnedOffer = facade.add(params)

        then:
            1 * Project.addOffer(projectId, _) >> { projId, offer -> offer }
            returnedOffer.name == params.name

        where:
            projectId | offerName
            1         | 'an Offer'
            15        | 'whasup!?'
            123       | 'doskonała oferta - kup teraz!'
    }
}
So we test a facade responsible for handling "add offer to the project" call triggered  somewhere in a GUI.
We want to ensure that static method Project.addOffer(long, Offer) will receive correct params when java.util.Map with user form input comes to the facade.add(params).
This is unit test, so how Project.addOffer() works is out of scope. Thus we want to stub it.

The most important is a GroovyMock(Project, global: true) statement.
What it does is modifing Project class to behave like a Spock's mock. 
GroovyMock() itself is a method inherited from Specification.  The global flag is necessary to enable mocking static methods.
However when one comes to the need of mocking static method, author of Spock Framework advice to consider redesigning of implementation. It's not a bad advice, I must say.

Another important thing are assertions at then: block. First one checks an interaction, if the Project.addOffer() method was called exactly once, with a 1st argument equal to the projectId and some other param (we don't have an object instance yet to assert anything about it).
Right shit operator leads us to the stub which replaces original method implementation by such statement.
As a good stub it does nothing. The original method definition has return type Offer. The stub needs to do the same. So an offer passed as the 2nd argument is just returned.
Thanks to this we can assert about name property if it's equal with the value from params. If no return was designed the name could be checked inside the stub Closure, prefixed with an assert keyword.

Worth of  mentioning is that if you want to track interactions of original static method implementation without replacing it, then you should try using GroovySpy instead of GroovyMock.

Unfortunately static methods declared at Java object can't be treated in such ways. Though regular mocks and whole goodness of Spock can be used to test pure Java code, which is awesome anyway :)No matter why, no matter is it a good idea. Sometimes one just wants to check or it's necessary to be done. Mock a static method, woot? Impossibru!

In pure Java world it is still a struggle. But Groovy allows you to do that really simple. Well, not groovy alone, but with a great support of Spock.

Lets move on straight to the example. To catch some context we have an abstract for the example needs. A marketing project with a set of offers. One to many.

import spock.lang.Specification

class OfferFacadeSpec extends Specification {

    OfferFacade facade = new OfferFacade()

    def setup() {
        GroovyMock(Project, global: true)
    }

    def 'delegates an add offer call to the domain with proper params'() {
        given:
            Map params = [projId: projectId, name: offerName]

        when:
            Offer returnedOffer = facade.add(params)

        then:
            1 * Project.addOffer(projectId, _) >> { projId, offer -> offer }
            returnedOffer.name == params.name

        where:
            projectId | offerName
            1         | 'an Offer'
            15        | 'whasup!?'
            123       | 'doskonała oferta - kup teraz!'
    }
}
So we test a facade responsible for handling "add offer to the project" call triggered  somewhere in a GUI.
We want to ensure that static method Project.addOffer(long, Offer) will receive correct params when java.util.Map with user form input comes to the facade.add(params).
This is unit test, so how Project.addOffer() works is out of scope. Thus we want to stub it.

The most important is a GroovyMock(Project, global: true) statement.
What it does is modifing Project class to behave like a Spock's mock. 
GroovyMock() itself is a method inherited from Specification.  The global flag is necessary to enable mocking static methods.
However when one comes to the need of mocking static method, author of Spock Framework advice to consider redesigning of implementation. It's not a bad advice, I must say.

Another important thing are assertions at then: block. First one checks an interaction, if the Project.addOffer() method was called exactly once, with a 1st argument equal to the projectId and some other param (we don't have an object instance yet to assert anything about it).
Right shit operator leads us to the stub which replaces original method implementation by such statement.
As a good stub it does nothing. The original method definition has return type Offer. The stub needs to do the same. So an offer passed as the 2nd argument is just returned.
Thanks to this we can assert about name property if it's equal with the value from params. If no return was designed the name could be checked inside the stub Closure, prefixed with an assert keyword.

Worth of  mentioning is that if you want to track interactions of original static method implementation without replacing it, then you should try using GroovySpy instead of GroovyMock.

Unfortunately static methods declared at Java object can't be treated in such ways. Though regular mocks and whole goodness of Spock can be used to test pure Java code, which is awesome anyway :)