Eiffel Programming Language

1. Eiffel Programming Language By David Riley and Jason Thorpe December 3, 2002

2. Eiffel Overview • Object-oriented • Motivation – designed to avoid some of the pitfalls of older OOP languages • Introduced in 1985 • Created by Bertrand Meyer • Developed by his company Interactive Software Engineering • Named after Gustav Eiffel (designer of Eiffel Tower) • “The Eiffel Tower was completed on time and within budget, which should happen if you use Eiffel for your software projects ”http://www.engin.umd.umich.edu/CIS/course.des/cis400/eiffel/eiffel.html#history

3. Eiffel Milestones • 1985: Bertrand Meyer and Jean Marc Nerson begin development of Eiffel • 1986: 1st Eiffel compiler presented (April), 1st Customer Deliveries (December) • 1987: Eiffel achieves commercial success • 1991: Non-profit International Consortium for Eiffel (NICE) is founded; NICE controls the standardization of the Eiffel language • 1991: Publication of "Eiffel the language" by Bertrand Meyer (Prentice Hall) • 1995: NICE presents Eiffel Library Kernel Standard (ELKS), which sets standards for basic Eiffel classes. • 1997: NICE and the Eiffel Consortium organize Eiffel Struggle `97. Prizes awarded for Eiffel applications and Eiffel libraries. http://www.halstenbach.de/eiffel/eiffel8.htm

4. Supporting Platforms • Eiffel Software's EiffelStudio environment is available for the major industry platforms: Windows, Linux, Unix, and VMS. These implementations are all source-code compatible.

5. Eiffel Compilers • ISE Eiffel v5.2 • free time-limited evaluation version; Windows and Unix • www.eiffel.com • SmartEiffel the GNU Eiffel compiler • Free; All ANSI C machines • http://smarteiffel.loria.fr/ • Iss-base • Commercial – free 90-day trial version; Windows and Unix • NonCommercial – free; Windows and Linux • http://www.halstenbach.com/ • Visual Eiffel • Commercial – free evaluation (limited features); Windows and Linux • http://www.object-tools.com/

6. Distinctive Features • Portable – runs on many platforms • Open System – has a C/C++ interface for code reusability • Melting Ice Technology – combines compilation with byte code interpretation for faster turnaround times after a change has occurred. • Design by Contract – enforced with assertions through invariance, preconditions and postconditions. • Automatic Documentation – documentation produced quickly by single click.

7. Distinctive Features (cont.) • Multiple Inheritance - a class can inherit from multiple parents • Repeated Inheritance - a class inherits from another through two or more parents • Statically Typed – catch errors at compile time; not run time • Dynamically Bound – guarantee of right operation being applied depending on target object

8. Areas of Application • Eiffel is not intended for any specific area but is used in: • Teaching • not stuck within the confines of a single environment • Eiffel allows students to focus on the concepts, not notational details • Educators have remarked that it is easier to teach C++, Smalltalk, or Java once Eiffel techniques are mastered. • Rapid Prototyping • covers analysis, design, and implementation in a single framework • Financial Applications

9. Attributes (Data) last_character:CHARACTER last_integer:INTEGER last_real:REAL last_string:STRING last_boolean :BOOLEAN Output routines put_character(c:CHARACTER) put_integer(i:INTEGER) put_real(r:REAL) put_string(s:STRING) put_boolean(b:BOOLEAN) put_new_line Input routines read_character read_integer read_real read_line -- result stored in last_string read_word -- result stored in last_string read_boolean I/O in Eiffel

10. Basics in Eiffel • I/O example: io.put_string(“Enter an Integer “); io.read_integer; int1 := io.last_integer; • Basic Data Types • INTEGER, CHARACTER, REAL, STRING, BOOLEAN • Comments (--)

11. Looping from--initialization until done -- BOOLEAN condition loop-- executable statements end Example from i := 1 until i = 10 loop io.put_int (i); io.new_line; i := i + 1; end Control Structures

12. Conditional ... if x > 10 then ... statements ... elseif x > 5 then ... elseif statements ... elseif x > 0 then ... more elseif statements ... else ... else statements ... end Example .. if x > 0 thenio.put_string(“x is positive”); elseif x < 0 thenio.put_string(“x is negative”); elseio.put_string(“x is 0”); end Control Structures

13. Multi-Branch inspect input_character; when 'y' then ... statements when 'n' then ... statements else ... if no match is found end Example ... State : INTEGER; State_1, State_2, State_3 : INTEGER is unique; ... inspect State when State_1 then some_action; when State_2 then some_other_action when State_3 then another_action; else no_action; end; Control Structures

14. Arrays in Eiffel • Declaration • scores :ARRAY[INTEGER]; • Creation • !!scores.make(1,100) • Functions • count, lower, upper. • Insertion • scores.put(<value>, <index>); • Access • scores.item(<index>);

15. Design by Contract class COUNTER feature count: INTEGER increment_by (inc: INTEGER) is require inc > 0 do -- Implementation goes here ensure count = old count + inc end end

16. Hello World • class HELLO_WORLD creation make feature make is do print("Hello World!!!! %N") end --make end -- class HELLO_WORLD

17. Hello World (cont.) • Class name - end (required) • Creation Clause – specifies the routines that may be called. • Feature Clauses – describes class features.

18. Type System • Strongly typed • Two categories: reference type, expanded type • Five basic types (expanded): INTEGER, REAL, DOUBLE, CHARACTER and BOOLEAN

19. Sorting Example class ARRAY_EXAMPLEcreation startfeature store:ARRAY[INTEGER]; -- function fill_array fills array with integers entered from keyboard fill_array is local index:INTEGER; do from index = store.lower -1 until index = store.upper loop index := index + 1; io.readint; store.put(io.lastint,index); end -- loop end -- fill_array

20. Sorting Example (cont.) -- function print array will print contents of array print_array is local index:INTEGER; do from index := store.lower-1 until index = store.upper loop index := index + 1; io.putint(store.item(index)); end -- loop end -- print_array

21. Sorting Example (cont.) -- function sort array will sort the elements of the array sort_array is local sorted:BOOLEAN; temp_item: INTEGER index, last :INTEGER; do from last := store.upper; sorted := false; until sorted or else last = store.lower loop from sorted := true index := store.lower -1 last := last-1 until index = last

22. Sorting Example (cont.) loop index := index + 1; if store.item(index) > store.item(index+1) then -- swap element with successor element temp_item := store.item(index+1); store.put(store.item(index),index+1); store.put(temp_item,index); sorted := false; end -- if end – loop end -- loop end -- sort_array

23. Sorting Example (cont.) start is do !!store.make(1,7); fill_array; sort_array; print_array; end -- start end -- ARRAY-EXAMPLE

24. References • http://www.engin.umd.umich.edu/CIS/course.des/cis400/eiffel/eiffel.html#history • http://www.halstenbach.de/eiffel/eiffel8.htm • http://www.faqs.org/faqs/eiffel-faq/ • http://www.pi.informatik.tu-darmstadt.de/inf1/eiff-ref/