ASP.NET PDF Viewer using C#, VB/NET

Aggregate operators are a powerful way of working with seq<type> values. However, F# also provides a convenient and compact syntax called sequence expressions for specifying sequence values that could be built using operations such as choose, map, filter, and concat. Sequence expressions can also be used to specify the shapes of lists and arrays. It is valuable to learn how to use sequence expressions: They are a compact way of specifying interesting data and generative processes. They are used to specify database queries when using data access layers such as Microsoft s Language Integrated Queries (LINQ). See 15 for examples of using sequence expressions in this way. They are one particular use of workflows, a more general concept that has several uses in F# programming. We discuss workflows in 9, and we show how to use them for asynchronous and parallel programming in 13.

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The procedure update_emp_info gets as parameters the checksum calculated previously along with other parameters. We then use an additional check in the where clause of the update statement to compare the checksum for current values in the row with the one we calculated previously. We return the number of rows updated as an out parameter so that the application can detect whether or not its update went through. 14 15 16 17 18 19 20 21 22 23 24 25 26 procedure update_emp_info( p_empno in number, p_new_sal in number, p_new_ename in varchar2, p_checksum in number, p_num_of_rows_updated in out number ) is begin p_num_of_rows_updated := 0; update emp set sal = p_new_sal, ename = p_new_ename where empno = p_empno and p_checksum = calc_checksum( empno, ename, sal ); p_num_of_rows_updated := sql%rowcount; end;

Finally, the function calc_checksum calculates the checksum by simply invoking the owa_opt_pkg.checksum method, passing in the ename, empno, and sal columns of the current row (I will explain the reason for formatting the empno and sal columns in a moment): 27 function calc_checksum( p_empno in number, p_ename in varchar2, 28 p_sal in number ) 29 return number 30 is 31 begin 32 return owa_opt_lock.checksum( to_char(p_empno,'0009') 33 ||'/' || p_ename || '/' || to_char(p_sal, '00009.99')); 34 end; 35 end; 36 / Package body created. The / separators used are required to take care of null values. The formatting we used in the empno and sal columns is required to ensure that the concatenation result is a unique value for any two different rows. Otherwise, we can have a combination where the individual values being concatenated are different, but the concatenated result is the same, eventually resulting in the same checksum. For example, the checksum for two columns whose values are 12 and 34 in one instance but 123 and 4 in another would be the same if we use simple concatenation, as follows: scott@ORA10G> select owa_opt_lock.checksum( 12 || 34) 25702 scott@ORA10G> select owa_opt_lock.checksum( 123 || 4) 25702 from dual; from dual;

The simplest form of a sequence expression is seq { for value in expr .. expr -> expr }. Here -> should be read as yield. This is simply a shorthand way of writing Seq.map over a range expression. For example, you can generate an enumeration of numbers and their squares as follows: > let squares = seq { for i in 0 .. 10 -> (i,i*i) };; val squares : seq<int * int> > squares;; val it : seq<int * int> = [ (0,0); (1,1); (2,4); (3,9); ... ] The more complete form of this construct is seq{ for pattern in seq -> expression }. The pattern allows you to decompose the values yielded by the input enumerable. For example, you can consume the elements of squares using the pattern (i,isquared): > seq { for (i,isquared) in squares -> (i,isquared,i*isquared) };; val it : seq<int * int * int> = [ (0,0,0); (1,1,1); (2,4,8); (3,9,27); ... ] The input seq can be a seq<type> or any type supporting a GetEnumerator method. (The latter is supported because some important types from the .NET libraries support this method without directly supporting the seq interface.) The following is an example where the input is a list of options. If the pattern fails to match the element of the enumerable, it is skipped, and no result is yielded for that element: > seq { for Some(nm) in [ Some("James"); None; Some("John") ] -> nm.Length };; val it : seq<int> = [ 5; 4 ]

This chapter is about COM+. We enumerate its features and look specifically at what steps you must take with .NET types for them to function in the COM+ environment.