Hello World for Eve

hello.eve

# Hello World

Eve is based on the concept of a single data store that you can search in and
commit to. Let's start by committing a record:

~~~
commit
  [#greeting message: "hello world"]
~~~

Here we're committing a record with the tag `greeting` and a field `message`
containing the string `hello world`. Tags are used to specify groups of related
records.

We can search for records. Let's search for this record and display it on the
screen:

~~~
search
  [#greeting message]

bind
  [#ui/text text: message]
~~~

Here we've created a new record. It's tagged with `#ui/text`. The Eve runtime
will search for records of this type and display them on the screen.

A search might return multiple records. We'll add a new record and see it
displayed:

~~~
commit
  [#greeting message: "howdy world"]
~~~

Eve blocks react to changes in the data store automatically. Let's take
advantage of this to add a clock:

~~~
commit
  [#time #system/timer resolution: 1000]
~~~

Here we're committing a new record tagged with `time`. It uses `#system/timer`
to create a timer that updates each second. Let's display it on the screen:

~~~
search
  [#time second]

bind
  [#ui/text text: second]
~~~

This time we're just binding a record. This is different than committing them,
as this record won't persist until explicitly removed.

We can add a `ui/button` record to draw a button on the screen.

~~~
commit
  [#ui/button #increment text: "+1"]
~~~

Now this button will be an element of type `increment` containing the text `+1`.
We will search for click events on this element and commit each click event to
the store:

~~~
search
  event = [#html/event/click element: [#increment]]

commit
  [#clicked event]
~~~

Here, we're finding all clicks on our `increment` elements, and committing a
record for each click.

Now our store contains a `clicked` record for each instance of us clicking on
the button. We can count these with the `gather/count` function, then bind a
text element that displays the result:

~~~
search
  how-many = gather/count[for: [#clicked]]

bind
  [#ui/text text: "The button has been clicked {{how-many}} times"]
~~~