This is a really noob question, i'm sorry but my search on the internet can't find the answer. I have the following code:
-- MODEL
type alias Model = Int
model : Model
model =
0
-- UPDATE
type Msg = Increment | Decrement | Reset
update : Msg -> Model -> Model
update msg model =
case msg of
Increment ->
model + 1
Decrement ->
model - 1
Reset ->
model = 0
I am trying to implement the reset that sets the model value to 0. But i'm getting a compilation error:
The = operator is reserved for defining variables. Maybe you want == instead? Or
maybe you are defining a variable, but there is whitespace before it?
Please help!
You only need to write the model's new value there. In this case, that'll be just 0:
Reset ->
0
Related
Im using following code to train my model
trip_model = sm.OLS(x_dependent, y_variables).fit()
and print summary as
trip_model.summary()
I just want to take only the following values out of Summary
F-statistic , coef
how to get it?
The value returned by the fit function is a RegressionResults structure. You can check the documentation to see how to access each particular value:
f_statistic = trip_model.fvalue
coef = trip_model.params
In update I would like to call my Tick Action every time Input is called.
The scenario is that a user enters a value in a text field, on update the model is updated via Input and then Tick is called and more stuff is performed on the model.
In 0.16 I could do something like this :
Input query ->
({ model | query = query }, Effects.tick Tick)
Tick clockTime ->
-- do something with clockTime
I'm not sure how to do this in 0.17.
I'm not sure if this would be a subscription and if it were, how you could go about configuring it to call Input then Action.
Any help is appreciated.
The functionality for retrieving the current time as an effect has been moved into a Task, in the Time module under Time.now.
http://package.elm-lang.org/packages/elm-lang/core/4.0.1/Time#now
You can reproduce your functionality by making the following changes:
1) Make sure there is a NoOp message available in your messages. Time.now returns a Task which we know will never fail, but we still need a failure message to hand to Task.perform
type Msg
= Input String
| Tick Time
| NoOp
2) Replace Effects.tick Tick with Time.now and Task.perform
Input query ->
( { model | query = query }
, Time.now |> Task.perform (\_ -> NoOp) Tick
)
If you don't like the NoOp message, there are other ways around it, such as using Debug.crash or performFailproof from Task.Extra (found here: http://package.elm-lang.org/packages/NoRedInk/elm-task-extra/2.0.0/Task-Extra#performFailproof)
Coming from react, I am learning to understand Elm.
In the Todomvc example code, there is the following code snippet:
-- How we update our Model on a given Msg?
update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
case msg of
NoOp ->
model ! [] <-- What is this?
What I (think I) understand, is that the update function takes in a msg of type Msg and a model of type Model, and returns a tuple of containing a Model and a Cmd Msg.
But how should I read the return statement?
model ! []
What does this statement mean? return a "model [something] empty list"?
Did I miss something in the docs where this is explained? (Googling "elm !" did not get me far :)
Update for Elm 0.19
Elm 0.19 has removed the exclamation point operator. You must now construct the tuple manually, as in (model, Cmd.none).
Original Answer for Elm 0.18
The exclamation point in model ! [] is just a short-hand function for (model, Cmd.batch []), which is the type returned from typical update statements. It is defined here
Note that this syntax is going away in the next version of Elm (0.19) so don't get into the habit of using it ;-)
You can use today, and with 0.19:
update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
case msg of
NoOp ->
(model, Cmd.none)
I want to define the structure of my function input.
This module defines my function (part of it is pseudo code):
-module(my_service).
-export([my_function/2]).
-type my_enum() :: 1 | 2 | 5.
-record(my_record, {id = null :: string(), name = null :: string(), myType = null :: my_enum()}).
-spec my_function(MyValue#my_record) -> Result#my_record.
my_function(ClientRequest, MyValue) when is_record(Entry, my_record) ->
Response = client:request(get, "http://www.example.com/api?value=" + MyValue#my_record.name),
case Response of
{ok, Status, Head, Body} ->
Result = parse_response(Body, my_record);
Error ->
Error
end.
This is how I want to call it:
-module(test1).
-import(io, [format/2]).
main(_) ->
application:start(inets),
MyTestValue = #my_record{name => "test value", myType => 2},
X = my_service:my_function(MyTestValue),
io:format("Response: ~p", [X]).
So, any idea how I can force the type of the function input to be of type my_record?
It's often handy to destructure a record directly in the function argument list, which also forces that argument to have the desired record type. For example, we can slightly modify your my_function/2 like this:
my_function(ClientRequest, #my_record{name=Name}=MyValue) ->
Response = client:request(get, "http://www.example.com/api?value=" ++ Name),
case Response of
{ok, Status, Head, Body} ->
Result = parse_response(Body, MyValue);
Error ->
Error
end.
Note how we're pattern-matching the second parameter MyValue: we're not only asserting that it's a #my_record{} instance, but we're also extracting its name field into the Name variable at the same time. This is handy because we use Name on the first line of the function body. Note that we also keep the parameter name MyValue because we pass it to parse_response/2 within the function body. If we didn't need it, we could instead write the function head like this:
my_function(ClientRequest, #my_record{name=Name}) ->
This would still have the desired effect of forcing the second argument to be of type #my_record{}, and would also still extract Name. If desired, you could extract other fields in a similar manner:
my_function(ClientRequest, #my_record{name=Name, id=Id}) ->
Both Name and Id are then available for use within the function body.
One other thing: don't use the atom null as a default for your record fields. The default for Erlang record fields is the atom undefined, so you should just use that. This is preferable to defining your own concept of null in the language.
I am newbie to neo4j and I really need help.
I have created nodes properties NAME, EMAIL and AGE. These nodes are having relationship: IS_FRIEND_OF with property SINCE with other nodes.
I have given property values in NAME as “A”, “B”, “C”, “D” and so on.
Now when I fire a query in console like: Start n=node(*) where n.NAME=’A’ return n;
It is giving an exception like: EntityNotFoundException: The property 'NAME' does not exist on Node[0]
Now if I add a property NAME = “” on node [0] and then fire the same query, it is providing the correct output. For small data set it can work but for larger ones specifying each property for node [0] doesn’t seems to be the good solution.
Is it the only workaround or something else and better can be applied?
STARTn=node(*) WHERE n.NAME! = "A" RETURN n
The exclamation mark will do the following:
TRUE if n.prop = value, FALSE if n is NULL or n.prop does not exist
Cypher has two special operators: ? and ! to use in this case to handle this exception
Using ? will evaluate to true if n.prop is missing:
START n=node(*) WHERE n.NAME? = "A" RETURN n
And using ! will evaluate to false if n.prop is missing:
START n=node(*) WHERE n.NAME! = "A" RETURN n