--- rexxpub: defaults: rony.yaml logo: rexx --- . slide cover # Procedural and Object-oriented Programming 1 . subtitle **Overview, Statements, Comparisons, Branches, Repetition** . cover-art . picture img/010_ooRexx_V18/p01-diagram-7.png # Why REXX and ooRexx? - Human-centered language (simple syntax) - easy syntax and therefore *quick* to learn . click - Powerful object-model - All important concepts of the object-oriented paradigm available . click - Scripting language - Automation ("remote controlling") of applications and operating systems like Linux (D-Bus) or Windows (Windows Scripting Engine) . click - BSF4ooRexx (Java-Bridge) - All of Java immediately available camouflaged as ooRexx . click - Easy entry into other programming languages (e.g.: Java, Python) # Resources . after - Course materials - Slides: [http://wi.wu.ac.at/rgf/wu/lehre/autowin/material/foils](http://wi.wu.ac.at/rgf/wu/lehre/autowin/material/foils) . click - Related seminar, diploma, bachelor and master theses - [https://wi.wu.ac.at/rgf/diplomarbeiten/](https://wi.wu.ac.at/rgf/diplomarbeiten/) . click - Book - Flatscher R.G.: "Introduction to Rexx and ooRexx – From Rexx to Open Object Rexx (ooRexx)", facultas Management Book Service . after - Browser based ooRexx workbench with numerous examples and debugging abilities by Josep Maria Blasco * ooRexx Playground: [https://rexx.epbcn.com/oorexx-wasm/](https://rexx.epbcn.com/oorexx-wasm/) .click - More goodies from Josep Maria Blasco * Josep Maria's GitHub: [https://github.com/JosepMariaBlasco](https://github.com/JosepMariaBlasco) # Getting ooRexx (as of 2025-09-05) - Rexx Language Association (non-profit SIG): [https://www.RexxLA.org](https://www.RexxLA.org) . click - Latest ooRexx (beta versions are usually stable, fully productive) - Installation packages (needs administration rights) - [https://sourceforge.net/projects/oorexx/files/oorexx/](https://sourceforge.net/projects/oorexx/files/oorexx/) - **Considerations:** - **Operating System:** Linux, MacOS or Windows - **Bitness:** 32bit (Linux, Windows) or 64bit (Linux, MacOS, Windows) - **Architecture:** x86, ARM, Apple M1, ... . click - Resources at WU: - Virtual PC labs: [https://labconnect.wu.ac.at/](https://labconnect.wu.ac.at/) - FAQ: [https://learn.wu.ac.at/open/distanzlehre/de/virtuellpc](https://learn.wu.ac.at/open/distanzlehre/de/virtuellpc) # History - 1979 – Mike F. Cowlishaw (IBM-Fellow) . after - **REXX**: Acronym for "**RE**structured e**X**tended e**X**ecutor" . after - Human-centric successor of “EXEC” language on IBM mainframes . after - Interactive (interpreter) . after - Keywords are English, resulting code looks like pseudo-code! . after - No reserved keywords unlike many other programming languages! . click - 1987 – IBM’s System Application Architecture (SAA) - Procedural script language for all IBM platforms - Commercial and open source versions available for all operating systems . click - 1996 – ANSI/INCITS "Programming Language – REXX" (INCITS 274:1996\[S2008\]) # History - Since 1990s – Development of an object-oriented REXX - Fully compatible with classic ("procedural") REXX but still with a simple syntax - Internally fully object-oriented (classic REXX statements are transformed) - Powerful object model (e.g. meta-classes, multiple inheritance) . click - 1996 – Mike F. Cowlishaw development of NetREXX - NetRexx-programs are translated into Java byte code - Simpler programming of the Java VM (\~30% less Code) - IBM handed over source code to RexxLA ([http://www.RexxLA.org/](http://www.RexxLA.org/)) - June, 8th, 2011 opensource released by RexxLA # History - May 2004 – Negotiations about open-sourcing Object Rexx - IBM: Manfred Schweizer, manager of IBM's REXX development team - RexxLA: Pam Taylor (experienced commercial manager, USA), Mark Hessling (maintainer of Regina and author of numerous Rexx libraries, Australia), Rony G. Flatscher (MIS professor, Austria/Europe) - October 2004 – Object REXX → "Open Object REXX" (ooRexx) - April 2005 – RexxLA releases the opensource version of ooRexx - ooRexx 5.2.0 released in May 2026 - BSF4ooRexx850 a bridge between ooRexx and Java is available - ooRexx 5.2.0 released, work on ooRexx 5.3.0 has started - Work on bridges from ooRexx to .NET, Python, Lua, and JavaScript started . slide kicker=Basics reference="Cf. rexxref.pdf (2.26. SAY)" # Minimal REXX-Program - The Hello World program is a tradition that dates back to 1974. ```rexx /* a comment */ SAY "Hello, my beloved world" ``` . click label Output: . after ```output Hello, my beloved world ``` . slide kicker=Basics # Notation of Program Text - Upper or lowercase spelling irrelevant - All characters of a statement will be translated into uppercase and executed . click blanks=all - Exception: Contents of a string remains unchanged - Strings are delimited by apostrophes (`'`) or by quotes (`"`) . click ```rexx "Richard", 'Richard', "\{[]}\gulp!öäüß!{niX }" ``` . click blanks=all - Multiple blank characters between symbols are reduced to one blank, removed around operators . click - Example: . with blanks=all ```rexx saY "\{[]}\gulp!öäüß!{niX }" reverse( Abc ) ``` . click - Becomes: . with blanks=all ```rexx SAY "\{[]}\gulp!öäüß!{niX }" REVERSE(ABC) ``` . slide kicker=Basics reference="Cf. rexxref.pdf (1.10. Structure and General Syntax)" # Characters - Characters outside of strings and comments must be from the following character set - Blank - **a** thru **z** - **A** thru **Z** - **0** thru **9** - Exclamation mark (**!**), backslash (**\\**), question mark (**?**), equal sign (**=**), comma (**,**), minus (**-**), plus (**+**), dot (**.**), Slash (**/**), parentheses (**()**), square brackets (**\[\]**), asterisk (**\***), tilde (**\~**), semicolon (**;**), colon (**:**) and underscore (**\_**) . slide kicker=Basics # Variables - Variables allow storing, changing, and retrieving strings with the help of a discretionary name called an *identifier* . blanks ```rexx A = "Hello, my beloved world" a="Hello, my beloved variable" A = a "- changed again." say a ``` . click label Output: . with blanks ```output Hello, my beloved variable - changed again. ``` . click - Identifiers must begin with a letter, an exclamation mark, a question mark or an underline character, followed by one or more of these characters, digits, and dots. . slide kicker=Basics reference="Cf. rexxref.pdf (3.4. ::CONSTANT)" # Constants - Constants never get their values changed - It is possible to use literals which are string constants appearing verbatim in an expression - If one wishes to name constants, then there are a few possibilities available, e.g. a) [The constant value is assigned to a variable, the value of which never gets changed in the entire program (after all, it is a constant!)]{.fragment} . after ```rexx Pi = 3.14159 ``` b) [In ooRexx use the `::constant name value`{.rexx} directive]{.fragment} . slide kicker=Basics reference="Cf. rexxref.pdf (1.10.3. Comments)" # Comments - Comments may be nested and are allowed to span multiple lines. ```rexx say 3 + /* This /**/ is a /* nested /* aha */ comment */ which spans multiple lines */ 4 ``` . click label Output: . with ```output 7 ``` . click - Line comments: at the end of a statement, comments follow after two consecutive dashes: . with ```rexx say 3 + 4 -- this yields "7" ``` . click label Output: . with ```output 7 ``` . slide kicker=Basics # Statements - Statements consist of all characters up to and including the semi-colon (**;**) . click - There may an arbitrary number of statements on a line . click - If the semi-colon is missing, then the end of a statement is assumed by the end of a line . after ```rexx /* Some comment */ SAY "Hello, my dear world"; ``` . click label Output: . with ```output Hello, my dear world ``` . slide kicker=Basics # Statements - Statements may span multiple lines, but you need to indicate this with the continuation character - A dash (**-**) or comma (**,**) as the very last character on the line . click level=1 ```rexx /* Some comment */ SAY "Hello," - "my beloved world"; ``` . click label level=1 Output: . with level=1 ```output Hello, my beloved world ``` . slide kicker=Basics # Block - A block is a statement, which may comprise an arbitrary number of statements . click - A block starts with the keyword **DO** and ends with **END** . columns 6 6 ruled level=1 . click ```rexx DO; SAY "Hello," ; SAY "world" ; END; ``` . next column . click ```rexx DO SAY "Hello," SAY "world" END ``` . end columns . with label level=1 Output: . click level=1 ```output Hello, world ``` . slide kicker=Basics reference="Cf. rexxref.pdf (1.11.2.3. Comparison)" # Comparisons (`test_expression`) - Two values (constant, variable, results of function calls) can be compared with the following (Infix) operators (Result: **0**=false or **1**=true) . plain steps level=1 | | | |---|---| | `=` | `equal` | | `<>` `\=` | `unequal` | | `<` | `smaller` | | `<=` | `smaller than` | | `>` | `greater` | | `>=` | `greater than` | . click - Negation of Boolean (**0**=false, **1**=true) values . plain steps each=with level=1 | | | |---|---| | **\\** | **Negator** | . slide kicker=Basics reference="Cf. rexxref.pdf (1.11.2.4. Logical (Boolean))" # Comparisons (`test_expression`) - Boolean values can be combined . plain level=1 | | | |---|---| | `&` | `"and" (true: if both arguments are true)` | | `|` | `"or" (true: if either argument is true)` | | `&&` | `"exclusive or" (true: if one argument is true and the other is false)` | . click - Boolean combinations can be evaluated in a specific order if enclosed in parentheses: . with plain tight | | | |---|---| | ` 0 & 1 | 1`{.rexx} | `Result: 1 (= true)`{.output} | | `(0 & 1) | 1`{.rexx} | `Result: 1 (= true)`{.output} | | ` 0 & (1 | 1)`{.rexx} | `Result: 0 (= false)`{.output} | . slide kicker=Basics # Comparisons (`test_expression`) . plain tight steps=cells | | | |---|---| | `a=1`{.rexx} | | | `b=2`{.rexx} | | | `x="Anton"`{.rexx} | | | `y=" Anton "`{.rexx} | | | `If a = 1 then ...`{.rexx} | `Result: 1 (= true)`{.output} | | `If a = a then ...`{.rexx} | `Result: 1 (= true)`{.output} | | `If a >= b then ...`{.rexx} | `Result: 0 (= false)`{.output} | | `If x = y then ...`{.rexx} | `Result: 1 (= true)`{.output} | | `If x == y then ...`{.rexx} | `Result: 0 (= false)`{.output} | | ` a <= b & (a = 1 | b > a)`{.rexx} | `Result: 1 (= true)`{.output} | | `\(a <= b & (a = 1 | b > a))`{.rexx} | `Result: 0 (= false)`{.output} | | `\a`{.rexx} | `Result: 0 (= false)`{.output} | . slide kicker=Basics reference="Cf. rexxref.pdf (2.10. IF)" # Branch - A branch determines which statement (block) should be executed as a result of a comparison (of a Boolean value) - `IF test_expression=.true THEN statement;`{.rexx} . click ```rexx IF age < 19 THEN SAY "Young." ``` . click - A branch can also determine what alternative statement (block) should be executed, in case the Boolean value is false - `IF test_expression=.true THEN statement; ELSE statement;`{.rexx} . click ```rexx IF age < 19 THEN SAY "Young." ELSE SAY "Old." ``` . click ```rexx IF age < 1 THEN DO SAY "Hello," SAY "my beloved world" END ``` . slide kicker=Basics reference="Cf. rexxref.pdf (2.27. SELECT)" # Branch - **Multiple selections (SELECT)** ```rexx SELECT WHEN test_expression THEN statement; WHEN test_expression THEN statement; /* ... additional WHEN-statements */ OTHERWISE statement; END ``` . click label Example: . with ```rexx SELECT WHEN age = 1 THEN SAY "Baby." ; WHEN age = 6 THEN SAY "Elementary school kid." ; WHEN age >= 10 THEN SAY "Big kid." ; OTHERWISE SAY "Unimportant." ; END ``` . slide kicker=Basics reference="Cf. rexxref.pdf (2.4. DO)" # Repetition - A block can be executed repeatedly ```rexx DO 3 SAY "Aua!" SAY "Oh!" END ``` . click label Output: . after numbered steps=0,1-2,3-4,5-6 each=after ```output Aua! Oh! Aua! Oh! Aua! Oh! ``` . slide kicker=Basics reference="Cf. rexxref.pdf (2.4. DO)" # Repetition - Using a variable to control the number of repetitions ```rexx a = 3 ... DO a SAY "Aua!"; SAY "Oh!" END ``` . click label Output: . after numbered steps=0,1-2,3-4,5-6 each=after ```output Aua! Oh! Aua! Oh! Aua! Oh! ``` . slide kicker=Basics reference="Cf. rexxref.pdf (2.4. DO)" # Repetition - Repetition using a loop variable ("**i**" in this example) ```rexx DO i = 1 TO 3 SAY "Aua!"; SAY "Oh!" i END ``` . click label Output: . after numbered steps=0,1-2,3-4,5-6 each=after ```output Aua! Oh! 1 Aua! Oh! 2 Aua! Oh! 3 ``` . slide kicker=Basics reference="Cf. rexxref.pdf (2.4. DO)" # Repetition - Repetition using a loop variable ("**i**" in this example) ```rexx DO i = 1 TO 3 BY 2 SAY "Aua!"; SAY "Oh!" i END ``` . click label Output: . after numbered steps=0,1-2,3-4 each=after ```output Aua! Oh! 1 Aua! Oh! 3 ``` . slide kicker=Basics reference="Cf. rexxref.pdf (2.4. DO)" # Repetition - Repetition using a control variable ("**i**" in this example) ```rexx DO i = 3.1 TO 5.7 BY 2.1 SAY "Aua!"; SAY "Oh!" i END ``` . click label Output: . after numbered steps=0,1-2,3-4 each=after ```output Aua! Oh! 3.1 Aua! Oh! 5.2 ``` . slide kicker=Basics reference="Cf. rexxref.pdf (2.4. DO)" # Repetition - Conditional repetition (evaluated at the beginning of the block) ```rexx i = 2 DO WHILE i < 3 SAY "Aua!";SAY "Oh!" i i = i + 1 END ``` . click label Output: . with ```output Aua! Oh! 2 ``` . slide kicker=Basics reference="Cf. rexxref.pdf (2.4. DO)" # Repetition - Conditional repetition (evaluated at the beginning of the block) ```rexx i = 3 DO WHILE i < 3 SAY "Aua!";SAY "Oh!" i i = i + 1 END ``` . click label Output: [**→** No output, because block is not executed!]{.fragment .afterPrevious} . slide kicker=Basics reference="Cf. rexxref.pdf (2.4. DO)" # Repetition - Exit condition (evaluated at the end of the block) ```rexx i = 3 DO UNTIL i > 1 SAY "Aua!";SAY "Oh!" i i = i + 1 END ``` . click label Output: . with ```output Aua! Oh! 3 ``` . slide kicker=Basics # Execution, 1 . col 2 2 ```rexx /* */ a = 3 b = "4" say a b say a b say a ||b say a ||b + 3 say a + b ``` . click label Output: . numbered steps=0,1,2,3,4,5 ```output 3 4 3 4 34 37 7 ``` . click . next column . blanks=all ```rexx /* */ a = 3 b = "4" say a b say a b say a ||b say a ||b + 3 say a + b ``` . end columns . slide kicker=Basics # Execution (Commands), 2 ```rexx /* */ "del *.*" ``` . with **or:** . click ```rexx /* */ ADDRESS SYSTEM "del *.*" ``` . with **or:** . click ```rexx /* */ a = "del *.*" a ``` . with **or:** . click ```rexx /* */ a = "del *.*" ADDRESS SYSTEM a ``` . slide card logo=none # Contact