khibino/haskell-relational-record
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Kazu Yamamoto 2014-12-20 15:07:08 +09:00
parent 256efd86c9
commit e0971d57b5
1 changed files with 30 additions and 26 deletions
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quickstart.md
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@ -22,14 +22,16 @@ To install the Haskell "relational-record" library, type as follows:
Let's define our first relation. Copy the following to "hello.hs":
import Data.Int (Int32)
import Database.Relational.Query
hello :: Relation () (Int32, String)
hello = relation $ return (value 0 >< value "Hello")
main :: IO ()
main = putStrLn $ show hello ++ ";"
{% highlight haskell %}
import Data.Int (Int32)
import Database.Relational.Query
hello :: Relation () (Int32, String)
hello = relation $ return (value 0 >< value "Hello")
main :: IO ()
main = putStrLn $ show hello ++ ";"
{% endhighlight %}
`hello` defines the fist relation. This "SELECT"s a constant tuple value (0,"Hello") from the (virtual) empty table. In other words, this relation just returns (0,"Hello").
@ -49,24 +51,26 @@ We got "0\|Hello"! Note that "dummy.db" is really a dummy file.
Next, let's compose relations. Copy the following to "helloworld.hs":
import Data.Int (Int32)
import Database.Relational.Query
hello :: Relation () (Int32, String)
hello = relation $ return (value 0 >< value "Hello")
world :: Relation () (Int32, String)
world = relation $ return (value 0 >< value "World!")
helloWorld :: Relation () (Int32, (String, String))
helloWorld = relation $ do
h <- query hello
w <- query world
on $ h ! fst' .=. w ! fst'
return $ h ! fst' >< (h ! snd' >< w ! snd')
main :: IO ()
main = putStrLn $ show helloWorld ++ ";"
{% highlight haskell %}
import Data.Int (Int32)
import Database.Relational.Query
hello :: Relation () (Int32, String)
hello = relation $ return (value 0 >< value "Hello")
world :: Relation () (Int32, String)
world = relation $ return (value 0 >< value "World!")
helloWorld :: Relation () (Int32, (String, String))
helloWorld = relation $ do
h <- query hello
w <- query world
on $ h ! fst' .=. w ! fst'
return $ h ! fst' >< (h ! snd' >< w ! snd')
main :: IO ()
main = putStrLn $ show helloWorld ++ ";"
{% endhighlight %}
This code defines queries called `hello` and `world`. And `helloworld` composes them by joining them on the first element of the tuples.