New Effective CAL essay: How do I create an abstract data type in CAL?

How do I create an abstract data type in CAL? An abstract data type is one whose internal representation can be changed without needing to modify the source code of client modules that make use of that type. For software maintainability, it is a good idea to make a type that is subject to change or enhancement into an abstract data type. Another reason to create an abstract data type is to enforce invariants for values of the type that can only be ensured by using constructor functions (i.e. functions that return values of that type). In principle it is simple to create an abstract data type in CAL. For an algebraic data type, make the type constructor public and all data constructors private. For a foreign data type, make the type constructor public and the implementation scope private. If a scope qualifier is omitted, the scope is taken to be private. For example, the Map algebraic data type has the public type constructor Map and the data constructors Tip and Bin are each private, so it is an abstract data type. /** A map from keys (of type {@code k@}) to values (of type {@code a@}). */ data public Map k a = private Tip | private Bin size :: !Int key :: !k value :: a leftMap :: !(Map k a) rightMap :: !(Map k a); There are a number of invariants of this type: the size field represents the number of elements in the map represented by its Bin value. The keys in leftMap are all less than key, which in turn is less than all the keys in rightMap. In particular, non-empty Map values can only be created if the key parameter type is a member of the Ord type class. Values of the Map type can be created outside the Cal.Collections.Map module only by using constructor functions such as insert: insert :: Ord k => k -> a -> Map k a -> Map k a; public insert !key value !map = ... The owner of the Cal.Collections.Map module must ensure that all invariants of the Map type are satisfied, but if this is done, then it will automatically hold for clients using this function. Some examples of foreign abstract data types are Color, StringNoCase and RelativeDate: data foreign unsafe import jvm private "java.awt.Color" public Color; data foreign unsafe import jvm private "java.lang.String" public StringNoCase; data foreign unsafe import jvm private "int" public RelativeDate; The private implementation scope for Color means that a foreign function whose type involves Color can only be declared in the Cal.Graphics.Color module where the Color type is defined. A foreign function declaration involving the Color type relies on the compiler knowing that the Color type corresponds to java.awt.Color to resolve the corresponding Java entity i.e. it must know about the implementation of the Color type. Having a private implementation scope means that the Color type can be changed to correspond to a different Java class, or indeed to be an algebraic type, without the risk of breaking client code. In all these three cases there are useful, and different, design reasons to adopt a private implementation scope: For RelativeDate, the Java implementation type int represents a coded Gregorian date value in the date scheme used by Crystal Reports. Not all int values correspond to valid dates, and the algorithm to map an int to a year/month/day equivalent is fairly complicated, taking into account things like Gregorian calendar reform. Thus, it is desirable to hide the implementation of this type. For StringNoCase, the implementation is more straightforward as a java.lang.String. The reason to adopt a private implementation scope is to ensure that all functions involving StringNoCase preserve the semantics of StringNoCase as representing a case-insensitive string value. Otherwise it is very easy for clients to declare a function such as: foreign unsafe import jvm "method replace" replaceChar :: StringNoCase -> Char -> Char -> StringNoCase; which does not handle case-insensitivity correctly, but is a perfectly valid declaration. This declaration results in a compilation error when it is placed outside the module in which StringNoCase is defined because of the private implementation scope of StringNoCase. For Color, the issue is somewhat more subtle. The java.awt.Color implementation type is semantically the same as the CAL Color type. The problem is that java.awt.Color is mutable (since it can be sub-classed to create a mutable type). It is preferable for a first-class CAL type to not be mutable, so we simply make the implementation scope private to ensure that this will be the case. A somewhat less encapsulated kind of abstract data type can be created using friend modules and protected scope. For example, if an algebraic type is public, and all its data constructors are protected, then the data constructors can be accessed in the friend modules of the module in which the type is defined. Effectively this means that the implementation of the semantics of the type stretches over the module in which the type is defined, and all of its friend modules. These must all be checked if the implementation of the type is modified. Given the merits of abstract data types discussed above, it is perhaps surprising that most of the core types defined in the Prelude module are not abstract data types. For example: Boolean, Char, Int, Double, String, List, Maybe, Either, Ordering, JObject, JList, and all record and tuple types are non-abstract types. There are different reasons for this, depending on the particular type involved. For example, Boolean, List, Maybe, Either and Ordering are all rather canonical algebraic data types with a long history in functional languages, with many standard functions using them. They are thus guaranteed never to change. In addition, their values have no particular design invariants that need to be enforced via constructor functions. Exposing the data constructors gives clients some additional syntactic flexibility in using values of the type. For example, they can pattern match on the values using case expressions or let patterns. Essentially the same explanation holds for record and tuple types. Although non-tuple record types are less canonical, they do correspond to the fundamental notion of an anonymous named-field product type. The "anonymous" here simply means that the programmer can create an entirely new record type simply by creating a value; the type does not have to be declared anywhere prior to use. Char, Int, Double, String, JObject and JList are foreign types where in fact part of the semantics of the type is that we want clients to know that the type is a foreign type. For example, we want clients to know that Prelude.Int is essentially the Java primitive unboxed int type, and has all the semantics you would expect of the Java int type i.e. this is quite different from RelativeDate which is using int as its implementation type in a very tactical way that we may choose to change. One can think of a public foreign type declaration with public implementation scope as simply introducing the Java type into the CAL namespace. One interesting point here is with CAL's naming convention for public foreign types. We prefix a type name by "J" (for "Java") for foreign types with public implementation type such that the underlying Java type is mutable. This is intended as mnemonic that the type is not a pure functional type and thus some caution needs to be taken when using it. For example, Prelude.JObject has public Java implementation type java.lang.Object. In the case where the underlying Java type is not mutable, we do not use the prefix, since even though the type is foreign; it is basically a first class functional type and can be freely used without concern. For example, Prelude.String has public Java implementation type java.lang.String. In the case where the implementation type is private, then the fact that the type is a foreign type, whether mutable or not, is an implementation detail and we do not hint at that detail via the name. Thus Color.Color has as its private Java implementation type the mutable Java type java.awt.Color. When creating abstract data types it is important to not inadvertently supply public API functions that conflict with the desired public semantics of the type. For example, if the type is publicly a pure-functional (i.e. immutable) type such as Color, it is important not to expose functions that mutate the internal Java representation. A more subtle case of inadvertently exposing the implementation of a type can occur with derived instances. For example, deriving the Prelude.Outputable and Prelude.Inputable type classes on a foreign type, whose implementation type is a mutable Java reference type, allows the client to gain access to the underlying Java value and mutate it
(by calling Prelude.output, mutating, and then calling Prelude.input). The solution in this case is to not derive Inputable and Outputable instances, but rather to define a custom Inputable and Outputable instance that copies the underlying values.

Hi Pandra801,
When you create a the external content type, please try to add a filter based on your select statement.
http://arsalkhatri.wordpress.com/2012/01/07/external-list-with-bcs-search-filters-finders/
Or, try to create a stored procedure based on your select statement, then create ECT using the SQL stored procedure.
A step by step guide in designing BCS entities by using a SQL stored procedure
http://blogs.msdn.com/b/sharepointdev/archive/2011/02/10/173-a-step-by-step-guide-in-designing-bcs-entities-by-using-a-sql-stored-procedure.aspx
I hope this helps.
Thanks,
Wendy
Wendy Li
TechNet Community Support

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Re: How do you create and use "common" type classes?

Hi,
You have 2 potential solutions in your case :
1- Sub-class TextNullable class of Framework and add your methods in the
sub-class.
This is the way Domain class work. Only Nullable classes are sub-classable.
This is usefull for Data Dictionary.
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2- Put your add on code on a specific class and instanciate it in your user
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http://perso.club-internet.fr/dnguyen/
Robinson, Richard a écrit:
I'm relatively new to forte and I'd like to know how can you handle utility
type classes that you want to use through out your application? Ideally
what I want is a static class with static methods.
Let's say that I have a StringUtil class that has a bunch of methods for
manipulating strings.
My problem is that we have code that runs on the client and code that runs
on the server. Both areas could use the StringUtil class, but from what I
understand, I have to create StringUtil in a plan and then create a server
object of type StringUtil. The server object will eventually get assigned
to a partition. That's not good since I really want the server object to
physically reside at the server end and at the client end. (Actually, I
don't want a server object, I just want to invoke a static method of a
static class).
Any clues on how to solve this problem would be appreciated.
Also, what is the url at Sage-it that has a summary of all emails that have
been posted to [email protected]? Perhaps this question has been
answered previously.
Thanks in advance
To unsubscribe, email '[email protected]' with
'unsubscribe forte-users' as the body of the message.
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To unsubscribe, email '[email protected]' with
'unsubscribe forte-users' as the body of the message.
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Hi Richard,
Your question about "utility classes" brings up a number of issues, all of
which are important to long-term success with Forte.
There is no such thing as a static method (method that is associated with a
class but without an implicit object reference - this/self/me "pointer") in
TOOL, nor is there such thing as a global method (method not associated
with a class at all). This is in contrast to C++, which has both, and
Java, which has static methods, but not global classes. Frequently, Forte
developers will write code like this:
result, num : double;
// get initial value for num....
tmpDoubleData : DoubleData = new;
tmpDoubleData.DoubleValue = num;
result = tmpDoubleData.Sqrt().DoubleValue;
tmpDoubleData = NIL; // send a hint to the garbage collector
in places where a C++ programmer would write:
double result, num;
// get initial value for num....
result = Math::Sqrt(num);
or a Java programmer would write:
double result, num;
// get initial value for num....
result = Math.sqrt(num);
The result of this is that you end up allocating an extra object now and
then. In practice, this is not a big deal memory-wise. If you have a
server that is getting a lot of hits, or if you are doing some intense
processing, then you could pre-allocate and reuse the data object. Note
that optimization has its own issues, so you should start by allocating
only when you need the object.
If you are looking for a StringUtil class, then you will want to use an
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you could subclass from TextNullable, and add methods. Note that you will
still have to instantiate an object and call methods on that object.
The next issue you raise is where the object resides. As long as you do
not have an anchored object, you will always have a copy of an object on a
partition. If you do not pass the object in a call to another partition,
the object never leaves. If you pass the object to another partition, then
the other partition will have its own copy of the object. This means that
the client and the server will have their own copies, which is the effect
you are looking for.
Some developers new to Forte will try to get around the lack of global
methods in TOOL by creating a user-visible service object and then calling
methods on it. If you have a general utility, like string handling, this
is a bad idea, since a service object can reside only on a single
partition.
Summary:
* You may find everything you want in TextData.
* Unless you anchor the object, the instance will reside where you
intuitively expect it.
* To patch over the lack of static methods in TOOL, simply allocate an
instance when required.
Feel free to email me if you have more questions on this.
At the bottom of each message that goes through the mailing list server,
the address for the list archive is printed:
http://pinehurst.sageit.com/listarchive/.
Good Luck,
CSB
-----Original Message-----
From: Robinson, Richard
Sent: Tuesday, March 02, 1999 5:44 PM
To: '[email protected]'
Subject: How do you create and use "common" type classes?
I'm relatively new to forte and I'd like to know how can you handle utility
type classes that you want to use through out your application? Ideally
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understand, I have to create StringUtil in a plan and then create a server
object of type StringUtil. The server object will eventually get assigned
to a partition. That's not good since I really want the server object to
physically reside at the server end and at the client end. (Actually, I
don't want a server object, I just want to invoke a static method of a
static class).
Any clues on how to solve this problem would be appreciated.
Also, what is the url at Sage-it that has a summary of all emails that have
been posted to [email protected]? Perhaps this question has been
answered previously.
Thanks in advance

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