Hyper doesn't provide any built in validation framework, but it makes it quite easy for you to do the job by providing simple data type Hyper.Form.Form which represent incomming GET or POST data. There is also some plumbing implemented for parsing incomming urlencoded data into Form value.
Let's look at simple example in which we are going to do some simple validation of incoming data.
We first declare our data types, and some instance which we will need later.
.. literalinclude:: FormSerialization.purs :language: haskell :start-after: start snippet datatypes :end-before: end snippet datatypes
In this example we use really simple approach to validation which only reports first encountered error:
.. literalinclude:: FormSerialization.purs :language: haskell :start-after: start snippet parsing :end-before: end snippet parsing
Now we are ready to write our handler. We use parseOrder to get a
value of type Either String Order from Either String Form,
where the String explains parsing errors. By pattern matching using
record field puns, we extract the beers and meal values, and respond
based on those values.
.. literalinclude:: FormSerialization.purs :language: haskell :start-after: start snippet onPost :end-before: end snippet onPost
Let's try this server out at the command line.
$ curl -X POST -d 'beers=6' http://localhost:3000
Missing field: meal
$ curl -X POST -d 'meal=Vegan&beers=foo' http://localhost:3000
Invalid number: foo
$ curl -X POST -d 'meal=Omnivore&beers=6' http://localhost:3000
Sorry, we do not serve meat here.
$ curl -X POST -d 'meal=Vegetarian&beers=6' http://localhost:3000
One Vegetarian meal and 6 beers coming up!