Simple .NET/ASP.NET PDF document editor web control SDK

Sequences are frequently used to represent the process of streaming data from an external source, such as from a database query or from a computer s file system. For example, the following recursive function constructs a seq<string> that represents the process of recursively reading the names of all the files under a given path. The return types of Directory. GetFiles and Directory.GetDirectories are string[], and as noted earlier, this type is always compatible with seq<string>. open System.IO let rec allFiles dir = Seq.append (dir |> Directory.GetFiles) (dir |> Directory.GetDirectories |> Seq.map allFiles |> Seq.concat) This gives the following type:

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function checksum(p_owner in varchar2, p_tname in varchar2, p_rowid in rowid) return number;

Here is an example of the function being used on one of our machines:

This chapter is on Web Services in the .NET Framework. We ll take a look at why you would want to use Web Services, we ll examine them from a vendor-neutral perspective to see how they provide for excellent cross-platform interoperability, and then we ll delve into some of the new features for Web Services that are built into version 2.0 of the .NET Framework. We ll wrap this chapter up with a quick look at Web Service Enhancements, an add-on package of functionality available from Microsoft.

It cannot be used for optimistic locking when being invoked by our JDBC program, since it needs to lock the row in order to calculate the checksum.

> allFiles @"c:\WINDOWS\system32";; val it : seq<string> = = seq ["c:\\WINDOWS\\system32\\$winnt$.inf"; "c:\\WINDOWS\\system32\\12520437.cpx"; "c:\\WINDOWS\\system32\\12520850.cpx"; "c:\\WINDOWS\\system32\\6to4svc.dll"; ...] The allFiles function is interesting partly because it shows many aspects of F# working seamlessly together: Functions are values: The function allFiles is recursive and is used as a first-class function value within its own definition. Pipelining: The pipelining operator |> provides a natural way to present the transformations applied to each subdirectory name. Type inference: Type inference computes all types in the obvious way, without any type annotations. NET interoperability: The System.IO.Directory operations provide intuitive primitives, which can then be incorporated in powerful ways using succinct F# programs. Laziness where needed: The function Seq.map applies the argument function lazily (on demand), which means subdirectories will not be read until really required. One subtlety with programming with on-demand or lazy values such as sequences is that side effects such as reading and writing from an external store should not in general happen until the lazy sequence value is actually consumed. For example, the previous allFiles function reads the top-level directory C:\ as soon as allFiles is applied to its argument. This may not be appropriate if the contents of C:\ are changing. You can delay the computation of the sequence by using the library function Seq.delay or by using a sequence expression, covered in the next section, where delays are inserted automatically by the F# compiler.

Let s look at an example. Consider the following package, opt_lock_chksum_demo: scott@ORA10G> create or replace package opt_lock_chksum_demo 2 as 3 procedure get_emp_details( p_empno in number, 4 p_ename in out varchar2, p_sal in out number, 5 p_row_checksum in out number ); 6 procedure update_emp_info( p_empno in number, 7 p_new_sal in number, p_new_ename in varchar2, 8 p_checksum in number, p_num_of_rows_updated in out number ); 9 function calc_checksum( p_empno in number, 10 p_ename in varchar2, p_sal in number ) return number; 11 end; 12 / The two methods in the package, get_emp_details and update_emp_info, perform the same functionality as the methods with same names in the previous sections. The third method, calc_checksum, calculates the checksum based on the column names that are being modified and the primary key column. Let s look at their definitions: scott@ORA10G> create or replace package body opt_lock_chksum_demo 2 as The following get_emp_details procedure performs a select to get the employee information that can be changed by the user (the ename and sal columns of the emp table). In the same select, it invokes the calc_checksum method to calculate a unique value based on the values of the two columns that can be changed and the primary key column empno. 3 4 5 6 7 8 9 10 11 12 procedure get_emp_details( p_empno in number, p_ename in out varchar2, p_sal in out number, p_row_checksum in out number ) is begin select ename, sal, calc_checksum( empno, ename, sal ) into p_ename, p_sal, p_row_checksum from emp where empno = p_empno; end;

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