[Lift] Re: Newbie: zero parameter functions, bind call-by-name function curiosity
On Oct 27, 8:52 am, Strom strommo...@gmail.com wrote:
I'm not sure if this is a scala or a lift related question, but when I
try to bind a submit button, I'm having some confusion on using zero
parameter functions as the () - Any parameter in the submit
signature.
The signature for the method in question is
SHtml.submit(value : String, func : () = Any, attrs : (String, String)
*)
1. My first question is about the following method definitions
def processForm () : Unit = {...}
vs
def processForm = {...} //no parentheses after method declaration
Why can I call processForm as well as processForm() for the first
example, but only processForm for the second example. If there is
scala/lift documentation on this simple question?
Because compiler already knows that processForm is a zero argument
function and accepts processForm call. In the second example you just
can't call a call-by-name using () as it would contradict its very
definition.
2. Why do I get a compiler error when I use the following code:
bind( ...
submit - SHtml.submit( Process Form, processForm() ) /*type
mismatch error*/
)
vs
bind( ...
submit - SHtml.submit( Process Form, processForm ) /*compiles
successfully*/
)
processForm() is a value not a function. It is the value returned by
processForm function while processForm is the function itself.
It's my impression that the above bind calls are equivalent given the
way the scala compiler behaves when I call processForm or
processForm().
Also, I wasn't even sure the method itself would allow the code to
compile. I thought I'd have to do () - processForm or () -
processForm().
The error I was getting was this:
error type mismatch
found : Unit
required : () - Any
Can someone please clarify? Thanks so much.
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[Lift] Re: Newbie: zero parameter functions, bind call-by-name function curiosity
Did you mean () = processForm by chance? () - processForm is a pair
of () and processForm's result.
-Ross
On Oct 27, 2009, at 2:52 AM, Strom wrote:
I'm not sure if this is a scala or a lift related question, but when I
try to bind a submit button, I'm having some confusion on using zero
parameter functions as the () - Any parameter in the submit
signature.
The signature for the method in question is
SHtml.submit(value : String, func : () = Any, attrs : (String,
String)
*)
1. My first question is about the following method definitions
def processForm () : Unit = {...}
vs
def processForm = {...} //no parentheses after method declaration
Why can I call processForm as well as processForm() for the first
example, but only processForm for the second example. If there is
scala/lift documentation on this simple question?
2. Why do I get a compiler error when I use the following code:
bind( ...
submit - SHtml.submit( Process Form, processForm() ) /*type
mismatch error*/
)
vs
bind( ...
submit - SHtml.submit( Process Form, processForm ) /*compiles
successfully*/
)
It's my impression that the above bind calls are equivalent given the
way the scala compiler behaves when I call processForm or
processForm().
Also, I wasn't even sure the method itself would allow the code to
compile. I thought I'd have to do () - processForm or () -
processForm().
The error I was getting was this:
error type mismatch
found : Unit
required : () - Any
Can someone please clarify? Thanks so much.
--~--~-~--~~~---~--~~
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Lift group.
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[Lift] Re: Newbie: zero parameter functions, bind call-by-name function curiosity
Yes Ross, I did mean () = processForm. Thanks for the clarification.
The one thing in moving from Java to Scala is that there are a lot of
things that look similar that aren't, as you've pointed out. Newbie
error caught ;)
Thanks Marius, I made that assumption, but it still bugs me that the
scala interpreter evaluates both the value and the function when I
use:
scala def testFunc() : Int = 3
scala testFunc
Int = 3
scalatestFunc()
Int = 3
Strom
On Oct 27, 7:19 am, Ross Mellgren dri...@gmail.com wrote:
Did you mean () = processForm by chance? () - processForm is a pair
of () and processForm's result.
-Ross
On Oct 27, 2009, at 2:52 AM, Strom wrote:
I'm not sure if this is a scala or a lift related question, but when I
try to bind a submit button, I'm having some confusion on using zero
parameter functions as the () - Any parameter in the submit
signature.
The signature for the method in question is
SHtml.submit(value : String, func : () = Any, attrs : (String,
String)
*)
1. My first question is about the following method definitions
def processForm () : Unit = {...}
vs
def processForm = {...} //no parentheses after method declaration
Why can I call processForm as well as processForm() for the first
example, but only processForm for the second example. If there is
scala/lift documentation on this simple question?
2. Why do I get a compiler error when I use the following code:
bind( ...
submit - SHtml.submit( Process Form, processForm() ) /*type
mismatch error*/
)
vs
bind( ...
submit - SHtml.submit( Process Form, processForm ) /*compiles
successfully*/
)
It's my impression that the above bind calls are equivalent given the
way the scala compiler behaves when I call processForm or
processForm().
Also, I wasn't even sure the method itself would allow the code to
compile. I thought I'd have to do () - processForm or () -
processForm().
The error I was getting was this:
error type mismatch
found : Unit
required : () - Any
Can someone please clarify? Thanks so much.
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[Lift] Re: Newbie: zero parameter functions, bind call-by-name function curiosity
On Oct 27, 8:50 pm, Strom strommo...@gmail.com wrote:
Yes Ross, I did mean () = processForm. Thanks for the clarification.
The one thing in moving from Java to Scala is that there are a lot of
things that look similar that aren't, as you've pointed out. Newbie
error caught ;)
Thanks Marius, I made that assumption, but it still bugs me that the
scala interpreter evaluates both the value and the function when I
use:
scala def testFunc() : Int = 3
scala testFunc
Int = 3
scalatestFunc()
Int = 3
Right ... and this is correct. Because there is no context the
interpreter (and compiler) assume that you mean a function-
application. But try this:
scala testFunc _
res5: () = Int = function
the _ here means eta expansion. A method is converted into a function.
SLS 6.25.5
But context matters:
scala def testFunc(): Int = 3
testFunc: ()Int
scala def other(f: () = Int) = f()
other: (() = Int)Int
scala other(testFunc)
res0: Int = 3
scala other(testFunc())
console:7: error: type mismatch;
found : Int
required: () = Int
other(testFunc())
^
In the above example textFunc and testFunc() means two different
things
Strom
On Oct 27, 7:19 am, Ross Mellgren dri...@gmail.com wrote:
Did you mean () = processForm by chance? () - processForm is a pair
of () and processForm's result.
-Ross
On Oct 27, 2009, at 2:52 AM, Strom wrote:
I'm not sure if this is a scala or a lift related question, but when I
try to bind a submit button, I'm having some confusion on using zero
parameter functions as the () - Any parameter in the submit
signature.
The signature for the method in question is
SHtml.submit(value : String, func : () = Any, attrs : (String,
String)
*)
1. My first question is about the following method definitions
def processForm () : Unit = {...}
vs
def processForm = {...} //no parentheses after method declaration
Why can I call processForm as well as processForm() for the first
example, but only processForm for the second example. If there is
scala/lift documentation on this simple question?
2. Why do I get a compiler error when I use the following code:
bind( ...
submit - SHtml.submit( Process Form, processForm() ) /*type
mismatch error*/
)
vs
bind( ...
submit - SHtml.submit( Process Form, processForm ) /*compiles
successfully*/
)
It's my impression that the above bind calls are equivalent given the
way the scala compiler behaves when I call processForm or
processForm().
Also, I wasn't even sure the method itself would allow the code to
compile. I thought I'd have to do () - processForm or () -
processForm().
The error I was getting was this:
error type mismatch
found : Unit
required : () - Any
Can someone please clarify? Thanks so much.
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