Extending programming language semantics while maintaining standard syntax through aliasing
A method is provided for allowing programmers to specify program execution control semantics using standard programming language syntax even when the standard language does not provide a language construct for specifying execution control. In a similar manner, the approach provides programmers the ability to extend the expressiveness of a language by introducing statements expressed in the syntax of a target programming language. A program written in a first programming language may be translated into statements of a second programming language, where the target programming language is more expressive than the first. This language-based approach preserves the standard syntax of the first programming language, allowing a program written with semantic extensions to be compiled and run according to the standard on any standards-compliant system.
1. A method comprising:
a code processor pre-processing a set of statements that conform to a computer programming language standard, said set of statements including a first aliasing directive and a second aliasing directive, both of which conform to a syntax defined by the computer programming language standard;
wherein said syntax specifies that an aliasing directive includes an alias expression and a substitute expression;
wherein the first aliasing directive includes a first alias expression and a first substitute expression and the second aliasing directive includes a second alias expression and a second substitute expression;
wherein a semantic specified by said computer programming language standard for an aliasing directive is that instances of an alias expression in the set of statements are replaced with a substitute expression corresponding to the aliasing directive during pre-processing of the set of statements;
wherein the second substitute expression specifies a processing directive having a semantic different than any semantic specified by said computer programming language standard for a substitute expression of an aliasing directive;
wherein said set of statements does not refer to the second alias expression outside of the second aliasing directive;
wherein said code processor pre-processing the set of statements includes:
replacing the first alias expression with the first substitute expression;
pre-processing the second aliasing directive by generating code to carry out the processing directive specified in the second substitute expression.
2. The method of claim 1 , wherein
the second aliasing directive contains a pragma for controlling query execution; and
in response to interpreting said pragma, the code processor executing said set of statements further comprises performing one of:
a) setting a timeout for a query;
b) controlling a number of parallel execution threads to execute a query; or
c) providing hints to a query optimizer for optimizing a query execution plan.
3. The method of claim 1 , wherein
said computer programming language standard defines a first programming language;
the substitute expression of said second aliasing directive contains program source code for a second programming language, wherein the program source code for the second programming language is not syntactically correct in said first programming language.
4. The method of claim 3 , wherein the code processor translates said set of statements in said first programming language into said second programming language.
5. The method of claim 1 , wherein the code processor is comprised of a programming language compiler.
6. The method of claim 1 , wherein the code processor is comprised of a programming language interpreter.
7. The method of claim 1 , wherein the second aliasing directive defines a namespace prefix.
8. The method of claim 1 , wherein the second aliasing directive defines a macro.
9. The method of claim 7 , wherein a substitute expression for the namespace prefix is a URI.
10. The method of claim 7 , wherein a substitute expression for the namespace prefix is a URL.
11. The method of claim 10 , wherein content retrieved at a location of the URL includes query execution control directives.
12. The method of claim 10 , wherein content retrieved at the URL includes one or more expressions coded in a second programming language.
13. A non-transitory computer-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors cause:
a code processor pre-processing a set of statements that conform to a computer programming language standard, said set of statements including a first aliasing directive and a second aliasing directive, both of which conform to a syntax defined by the computer programming language standard;
wherein said syntax specifies that an aliasing directive includes an alias expression and a substitute expression;
wherein the first aliasing directive includes a first alias expression and a first substitute expression and the second aliasing directive includes a second alias expression and a second substitute expression;
wherein a semantic specified by said computer programming language standard for an aliasing directive is that instances of an alias expression in the set of statements are replaced with a substitute expression corresponding to the aliasing directive during pre-processing of the set of statements;
wherein the second substitute expression specifies a processing directive having a semantic different than any semantic specified by said computer programming language standard for a substitute expression of an aliasing directive;
wherein said set of statements does not refer to the second alias expression outside of the second aliasing directive;
wherein said code processor pre-processing the set of statements includes:
replacing the first alias expression with the first substitute expression;
pre-processing the second aliasing directive by generating code to carry out the processing directive specified in the second substitute expression.
14. The non-transitory computer-readable storage medium of claim 13 , wherein
the second aliasing directive contains a pragma for controlling query execution; and
in response to interpreting said pragma, the code processor executing said set of statements further comprises performing one of:
a) setting a timeout for a query;
b) controlling a number of parallel execution threads to execute a query; or
c) providing hints to a query optimizer for optimizing a query execution plan.
15. The non-transitory computer-readable storage medium of claim 13 , wherein
said computer programming language standard defines a first programming language;
the substitute expression of said second aliasing directive contains program source code for a second programming language, wherein the program source code for the second programming language is not syntactically correct in said first programming language.
16. The non-transitory computer-readable storage medium of claim 15 , wherein the code processor translates said set of statements in said first programming language into said second programming language.
17. The non-transitory computer-readable storage medium of claim 13 , wherein the code processor is comprised of a programming language compiler.
18. The non-transitory computer-readable storage medium of claim 13 , wherein the code processor is comprised of a programming language interpreter.
19. The non-transitory computer-readable storage medium of claim 13 , wherein the second aliasing directive defines a namespace prefix.
20. The non-transitory computer-readable storage medium of claim 13 , wherein the second aliasing directive defines a macro.
21. The non-transitory computer-readable storage medium of claim 19 , wherein a substitute expression for the namespace prefix is a URI.
22. The non-transitory computer-readable storage medium of claim 19 , wherein a substitute expression for the namespace prefix is a URL.
23. The non-transitory computer-readable storage medium of claim 22 , wherein content retrieved at a location of the URL includes query execution control directives.
24. The non-transitory computer-readable storage medium of claim 22 , wherein content retrieved at the URL includes one or more expressions coded in a second programming language.