Sas® Macro Design Patterns


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The qualities which SAS® macros share with object-oriented languages account for the power of macro
programming. This paper illustrates some examples of specific design patterns which can be partially or fully
implemented with the SAS macro language. The material is intermediate to advanced, and assumes knowledge of
macros and macro variables. The goal is to illustrate best practices for SAS macro programming.

Published in: Technology

Sas® Macro Design Patterns

  1. 1. SAS® Macro Design g Patterns Mark Tabladillo Ph D Ph.D. Software Developer, MarkTab Consulting Associate Faculty, University of Phoenix Atlanta, GA ,
  2. 2. Introduction Experienced SAS programmers use macros regularly The Macro Facility has two components The macro processor (engine or mechanism) The macro language (syntax)
  3. 3. Power of SAS Macros Power Source Definition Examples Function The SAS System has added specific • %LENGTH macro functions. • %EVAL • %SYSFUNC See SAS Institute (2005) Implementation The SAS System defines specific ways • Global versus local macro that macro variables and macros variables resolve. • %DO inside macros See SAS Institute (2005) Structure The SAS Macro language has some To some extent: characteristics of object-oriented object- • Encapsulation languages. • Polymorphism • Inheritance See Tabladillo (2005)
  4. 4. SAS Macro Design Patterns Focus: Focus: structural power Approach: A h Approach: provide examples on how id l h macros can implement some aspects of object- i object-oriented d i patterns bj d design Mission: Mission: to provide specific design ideas for structuring macros in the most powerful way possible
  5. 5. Outline First: First: Illustrate three specific ways to trick the SAS macro language to emulate some properties of object-oriented languages. object- Second: Second: Answer what a design pattern is and why design patterns are useful. Third: List seven specific design patterns and provide SAS macro language examples. Finally: Provide some general application advice.
  6. 6. Overview How to trick the SAS Macro Language Why design patterns are useful Six specific design patterns General application development advice pp p
  7. 7. How to Trick the SAS Macro Language Trick One – emulate inheritance by cutting and pasting text There is no %INHERIT
  8. 8. How to Trick the SAS Macro Language Trick Two – emulate all types of variables with macro variables Macro variables are inherently character
  9. 9. How to Trick the SAS Macro Language %macro interface(char, num, array, macro); ( , , y, ); %local major; %macro breakarray(m, n, p, q); data _null_; call symput('major',&m); run; %put &m &n &p &q; %mend breakarray; %macro submacro(a, b); %put &a &b; %mend submacro; %put &char &num &array &macro; * Break up the array; %breakarray&array.; %put &major; * Call the named macro; %&macro.; %mend interface; %interface (char=character, num=2005, array=(1,2,3,4), macro=submacro(a=5,b=c));
  10. 10. How to Trick the SAS Macro Language Trick Three – emulate public functions (or methods) by applying nested macros Macros do not expose internal functions However, developers can write nested macros
  11. 11. Overview How to trick the SAS Macro Language Wh d i patterns are useful Why design f l Six specific design patterns General application development advice
  12. 12. Design Pattern Fundamentals Pattern – a solution to a problem in context Patterns provide a way to solve commonly recurring problems with two l i bl ih goals: Reuse Solutions Establish Common Terminology
  13. 13. Overview How to trick the SAS Macro Language Wh d i patterns are useful Why design f l Six specific design patterns General application development advice
  14. 14. FACADE: SIMPLIFY A COMPLEX SYSTEM Façade Pattern Key Features Intent You want to simplify how to use an existing system. You need to define your own interface interface. Problem You need to use only a subset of a complex system. Or you need to interact with the system in a particular way. Solution The Facade presents a new interface for the client of the existing system to use. Consequences The Façade simplifies the use of the required subsystem. However, since the Façade is not complete, certain functionality may be unavailable to the client. il bl h li
  15. 15. FACADE: SIMPLIFY A COMPLEX SYSTEM FULLY IMPLEMENTED EXAMPLE %macro facade(dataset); proc freq data=&dataset.; tables year*sales/list missing; run; proc means data=&dataset.; var annualSales totalEmployees sumTurnover; run; %mend facade; %facade(dataset=sales.ca200503); %facade(dataset=sales.ca200510); %facade(dataset=sales.ca200511); %facade(dataset=sales ca200511);
  16. 16. STRATEGY: USE DIFFERENT BUSINESS RULES DEPENDING ON CONTEXT Strategy Pattern Key Features Intent Allows you to use different business rules or algorithms depending on the context in which they occur. Problem The selection of an algorithm that needs to be applied depends upon the client making the request or the data being acted upon. If you simply have a rule in place that does not change, you do not need a Strategy pattern. Solution Separates the selection of the algorithm from the implementation of the algorithm. Allows for the selection to be made based upon context. Consequences • The Strategy pattern defines a family of algorithms. • Switches and/or conditionals can be eliminated. • You must invoke all algorithms in the same way (they must all have the same interface). interface)
  17. 17. STRATEGY: USE DIFFERENT BUSINESS RULES DEPENDING ON CONTEXT FULLY IMPLEMENTED EXAMPLE data work.taxExample; length grossAmount totalTax 8; grossAmount = 34000; run; %macro calculateTaxes(dataset,county); %macro taxStrategy(county); % ( ) %macro DeKalb; totalTax = grossAmount * 0.06; %mend deKalb; %macro Fulton; totalTax = grossAmount * 0 075; 0.075; %mend Fulton; %macro Gwinnett; totalTax = grossAmount * 0.06; %mend Gwinnett; %if &county. = DeKalb or &county. = Fulton or &county. = Gwinnett %then %&county.; %mend taxStrategy; data &dataset.; set &dataset.; %taxStrategy(&county.); run; proc print d t i t data=&dataset.; d t t run; %mend calculateTaxes; %calculateTaxes(dataset=work.taxExample, county=Fulton);
  18. 18. SINGLETON: HAVE ONLY ONE OBJECT AVAILABLE Decorator Pattern Key Features Intent You want to have only one of an object but there is no global object that controls the instantiation of the object. Problem Several different client objects need to refer to the same thing and you want to ensure that you do not have more than one of them. Solution Guarantees one instance. Consequences Clients need not concern themselves whether an instance of the singleton object exists. g j
  19. 19. SINGLETON: HAVE ONLY ONE OBJECT AVAIABLE Fully Implemented Singleton Pattern: Only one SAS Macro is allowed Only one SAS local named variable Only one SAS global named variable Only one instance of a base SAS session y
  20. 20. DECORATOR: ATTACH ADDITIONAL RESPONSIBILITIES DYNAMICALLY Decorator Pattern Key Features Intent Attach additional responsibilities to an object dynamically. Problem The object that you want to use does the basic functions you require. However, you may need to add some additional functionality to the object occurring before or after the object’s base functionality. y Solution Allows for extending the functionality of an object without resorting to subclassing. Consequences Functionality that is to be added resides in small objects. The advantage is the ability to dynamically add this function before or after the core functionality.
  21. 21. DECORATOR: ATTACH ADDITIONAL RESPONSIBILITIES DYNAMICALLY PARTIALLY IMPLEMENTED DECORATOR PATTERN %macro messyMacro(num,char); * Messy Macro; %put MessyMacro &num. &char.; %mend messyMacro; %macro decoratorBefore(parameters); %put Before; %messyMacro&parameters.; %mend decoratorBefore; % %macro d t B f decoratorBeforeAndAfter(parameters); A dAft ( t ) %put Before; %messyMacro&parameters.; %put After; %mend decoratorBeforeAndAfter; %macro decoratorAfter(parameters); %messyMacro&parameters.; %put After; %mend decoratorAfter; %decoratorBeforeAndAfter(parameters=(num=1,char=SAS));
  22. 22. TEMPLATE METHOD: APPLY DISCIPLINE TO THE FUNCTIONS AVAILABLE INSIDE MACROS Template Method Pattern Key Features Intent Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Redefine the steps in an algorithm without changing the algorithm’s structure Problem There is a procedure or set of steps to follow that is consistent at one level of detail, but individual steps may have different implementations at a lower level of detail. Solution Allows for definition of substeps that vary while maintaining a consistent basic process. Consequences Templates provide a good platform for code reuse. They are also helpful in ensuring the required steps are implemented.
  23. 23. TEMPLATE METHOD: APPLY DISCIPLINE TO THE FUNCTIONS AVAILABLE INSIDE MACROS %macro accessSAS(connectParameters,selectRecordParameters); %macro accessSQLServer(connectParameters,selectRecordParameters); %macro connectDB(num,char); %macro connectDB(num,char); %put SAS ConnectDB; %put SQL Server ConnectDB; %mend connectDB; %mend connectDB; %macro selectRecords(num,char); %macro selectRecords(num,char); %put SAS Record Selection; %put SQL Server Record Selection; %mend selectRecords; %mend selectRecords; %macro doQuery; %macro doQuery; * doQuery is the same for all macros; * doQuery is the same for all macros; %connectDB&connectparameters.; %connectDB&connectparameters.; %selectRecords&selectRecordParameters.; %selectRecords&selectRecordParameters.; %mend doQuery; %mend doQuery; %doQuery; %doQuery; %mend accessSAS; %mend accessSQLServer; PARTIALLY IMPLEMENTED TEMPLATE METHOD: Two different macros, same nested macros %accessSAS(connectParameters=(num=1,char=SAS), selectRecordParameters=(num=2,char=SAS)); %accessSQLServer(connectParameters=(num=1,char=SQLServer), selectRecordParameters=(num=2,char=SQLServer));
  24. 24. ANALYSIS MATRIX: HIGH- HIGH- VOLUME MACRO PROCESSING Analysis Matrix Method Pattern Key Features Intent Provide a systematic way to surface varying dimensions of change. Problem Variations in the system need to be made explicit so that applying design patterns becomes easier. Solution Create a matrix which documents the concepts which are varying. p y g Matrix creation can help the developer discover the concepts that are varying, find points of commonality, and uncover missing requirements. Consequences The final design is optimized for the surfaced dimensions, and dimensions refactoring may be required if dimensions are added or removed.
  25. 25. ANALYSIS MATRIX: HIGH- HIGH- VOLUME MACRO PROCESSING U.S. Sales Canadian Sales German Sales Calculate freight Combination Combination Combination Verify address Combination Combination Combination Calculate tax Combination Combination Combination Money Combination Combination Combination Dates Combination Combination Combination Maximum Combination Combination Combination weight Analysis Matrix Example (Shalloway and Trott, 2005, p. 286)
  26. 26. Overview How to trick the SAS Macro Language Why design Wh d i patterns are useful f l Six specific design patterns General application development advice
  27. 27. General Application Advice The Th examples ill l illustrate conceptual design ld i patterns The examples could be used as is, or combined with one another Consider upgrading to SAS/AF Most optionally licensed products represent procedures which extend base SAS
  28. 28. Conclusion This presentation: p Provided tricks for object-oriented emulation object- Defined and defended design patterns Demonstrated fully or partially implemented design patterns Provided application advice Read more (books or web) on design patterns to deepen your topical understanding
  29. 29. References Fowler, Martin (1999), Refactoring: Improving the Design of Existing Code, Code, Reading, MA: Addison Wesley Longman, Inc. Gamma, E., Helm, R., Johnson, R., Vlissides, J. (1995), Design Patterns: Elements of Reusable Object-Oriented Software, Reading MA: Object- Software, Reading, Addison Wesley Longman, Inc. SAS Institute Inc. (2005), SAS OnlineDoc® 9.1.3, Cary, NC: SAS 9.1.3, Institute, Inc. Shalloway, A., and Trott, J. (2005), Design Patterns Explained: a New Perspective on Object-Oriented Design (Second Edition), Boston MA: Object- Edition), Boston, Addison- Addison-Wesley, Inc. Tabladillo, M. (2005), “Macro Architecture in Pictures”, SUGI ( Proceedings, Proceedings, 2005.
  30. 30. Contact Information Mark Tabladillo Software Developer, MarkTab C S f D l M kT b Consulting li