Ada is an actively used programming language created in 1980. Ada is a structured, statically typed, imperative, wide-spectrum, and object-oriented high-level computer programming language, extended from Pascal and other languages. It has built-in language support for design-by-contract, extremely strong typing, explicit concurrency, offering tasks, synchronous message passing, protected objects, and non-determinism. Ada improves code safety and maintainability by using the compiler to find errors in favor of runtime errors. Read more on Wikipedia...
- Ada ranks in the top 1% of languages
- the Ada website
- the Ada wikipedia page
- Ada first appeared in 1980
- file extensions for Ada include adb, ads and ada
- See also: spark, ravenscar-profile, algol-68, pascal, smalltalk, java, eiffel, chapel, nim, pl-sql, plpgsql, ruby, rust, seed7, sql-psm, vhdl, unicode, lisp, setl, algol, algol-60, apse
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Example code from the Hello World Collection:
-- Hello World in Ada with Text_IO; procedure Hello_World is begin Text_IO.Put_Line("Hello World!"); end Hello_World;
Example code from Wikipedia:
with Ada.Text_IO; use Ada.Text_IO; procedure Traffic is type Airplane_ID is range 1..10; -- 10 airplanes task type Airplane (ID: Airplane_ID); -- task representing airplanes, with ID as initialisation parameter type Airplane_Access is access Airplane; -- reference type to Airplane protected type Runway is -- the shared runway (protected to allow concurrent access) entry Assign_Aircraft (ID: Airplane_ID); -- all entries are guaranteed mutually exclusive entry Cleared_Runway (ID: Airplane_ID); entry Wait_For_Clear; private Clear: Boolean := True; -- protected private data - generally more than just a flag... end Runway; type Runway_Access is access all Runway; -- the air traffic controller task takes requests for takeoff and landing task type Controller (My_Runway: Runway_Access) is -- task entries for synchronous message passing entry Request_Takeoff (ID: in Airplane_ID; Takeoff: out Runway_Access); entry Request_Approach(ID: in Airplane_ID; Approach: out Runway_Access); end Controller; -- allocation of instances Runway1 : aliased Runway; -- instantiate a runway Controller1: Controller (Runway1'Access); -- and a controller to manage it ------ the implementations of the above types ------ protected body Runway is entry Assign_Aircraft (ID: Airplane_ID) when Clear is -- the entry guard - calling tasks are blocked until the condition is true begin Clear := False; Put_Line (Airplane_ID'Image (ID) & " on runway "); end; entry Cleared_Runway (ID: Airplane_ID) when not Clear is begin Clear := True; Put_Line (Airplane_ID'Image (ID) & " cleared runway "); end; entry Wait_For_Clear when Clear is begin null; -- no need to do anything here - a task can only enter if "Clear" is true end; end Runway; task body Controller is begin loop My_Runway.Wait_For_Clear; -- wait until runway is available (blocking call) select -- wait for two types of requests (whichever is runnable first) when Request_Approach'count = 0 => -- guard statement - only accept if there are no tasks queuing on Request_Approach accept Request_Takeoff (ID: in Airplane_ID; Takeoff: out Runway_Access) do -- start of synchronized part My_Runway.Assign_Aircraft (ID); -- reserve runway (potentially blocking call if protected object busy or entry guard false) Takeoff := My_Runway; -- assign "out" parameter value to tell airplane which runway end Request_Takeoff; -- end of the synchronised part or accept Request_Approach (ID: in Airplane_ID; Approach: out Runway_Access) do My_Runway.Assign_Aircraft (ID); Approach := My_Runway; end Request_Approach; or -- terminate if no tasks left who could call terminate; end select; end loop; end; task body Airplane is Rwy : Runway_Access; begin Controller1.Request_Takeoff (ID, Rwy); -- This call blocks until Controller task accepts and completes the accept block Put_Line (Airplane_ID'Image (ID) & " taking off..."); delay 2.0; Rwy.Cleared_Runway (ID); -- call will not block as "Clear" in Rwy is now false and no other tasks should be inside protected object delay 5.0; -- fly around a bit... loop select -- try to request a runway Controller1.Request_Approach (ID, Rwy); -- this is a blocking call - will run on controller reaching accept block and return on completion exit; -- if call returned we're clear for landing - leave select block and proceed... or delay 3.0; -- timeout - if no answer in 3 seconds, do something else (everything in following block) Put_Line (Airplane_ID'Image (ID) & " in holding pattern"); -- simply print a message end select; end loop; delay 4.0; -- do landing approach... Put_Line (Airplane_ID'Image (ID) & " touched down!"); Rwy.Cleared_Runway (ID); -- notify runway that we're done here. end; New_Airplane: Airplane_Access; begin for I in Airplane_ID'Range loop -- create a few airplane tasks New_Airplane := new Airplane (I); -- will start running directly after creation delay 4.0; end loop; end Traffic;
Last updated August 9th, 2020