write-projection-function.md

Write a Projection Function

Let's enrich our HelloWorld application by adding functionality that allows us to read the label we have just created.

To achieve this, we add a special type of function, a projection function. You can think of it as a read function and you can find more details about it under interface.md.

We're adding a new file to accomodate our projection function.

{% code title="~/HelloWorld/" %}

touch GetMessage.juvix

{% endcode %}

We can now specify GetMessage.juvix. It will take an encodedResource parameter of type Nat. As the name suggests, this is an encoded resource object which we will first apply anomaDecode to, then access its label via Resource.label. We finally retrieve the underlying String type by applying another anomaDecode.

{% code title="GetMessage.juvix" %}

module GetMessage;

import Stdlib.Prelude open;
import Applib open;

--- Extract the message from a HelloWorld ;Resource;
main (resource : Resource) : String :=
  resource |> Resource.label |> builtinAnomaDecode;

{% endcode %}

In the following chapter, we will compile and "deploy" our code locally.