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Ada

Ada - Programming language

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Ada is a programming language created in 1980 by Jean Ichbiah.

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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...


Example from Compiler Explorer:
-- This pragma will remove the warning produced by the default -- CE filename and the procedure name differing, -- see : https://gcc.gnu.org/onlinedocs/gcc-8.2.0/gnat_rm/Pragma-Source_005fFile_005fName.html#Pragma-Source_005fFile_005fName pragma Source_File_Name (Square, Body_File_Name => "example.adb"); -- Type your code here, or load an example. function Square(num : Integer) return Integer is begin return num**2; end Square; -- Ada 2012 also provides Expression Functions -- (http://www.ada-auth.org/standards/12rm/html/RM-6-8.html) -- as a short hand for functions whose body consists of a -- single return statement. However they cannot be used as a -- compilation unit. -- function Square(num : Integer) return Integer is (num**2);
Example from Riju:
with Ada.Text_IO; procedure Main is begin Ada.Text_IO.Put_Line("Hello, world!"); end Main;
Example from hello-world:
with Ada.Text_IO; procedure Hello_World is use Ada.Text_IO; begin Put_line ("Hello World"); end Hello_World;
-- Hello World in Ada with Text_IO; procedure Hello_World is begin Text_IO.Put_Line("Hello World!"); end Hello_World;
Example 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;
abort else new return abs elsif not reverse abstract end null accept entry select access exception of separate aliased exit or some all others subtype and for out synchronized array function overriding at tagged generic package task begin goto pragma terminate body private then if procedure type case in protected constant interface until is raise use declare range delay limited record when delta loop rem while digits renames with do mod requeue xor

Language features

Feature Supported Token Example
Scientific Notation
Fixed Point Numbers
Integers
-- [0-9_]+
Floats
-- [0-9_]+\.[0-9_]*
Hexadecimals
-- [0-9_]+#[0-9a-f_\.]+#
Conditionals
Functions
While Loops
Booleans True False
Strings "
"Hello world"
Assignment :=
Print() Debugging Text_IO.Put_Line
Line Comments --
-- A comment
Case Insensitive Identifiers
with Gnat.Io; use Gnat.Io;
procedure Numbers is
   Score: Integer;
   F: Float := 1.0;
begin
   Score := 3 + 2#1011#;
   Put(score);
   New_Line;
   Score := Score + 1_000_000;
   Put(Score);
   New_Line;
end Numbers;
Operator Overloading
Directives
Comments
-- A comment
Generics
generic
   Max_Size : Natural; -- a generic formal value
   type Element_Type is private; -- a generic formal type; accepts any nonlimited type
package Stacks is
   type Size_Type is range 0 .. Max_Size;
   type Stack is limited private;
   procedure Create (S : out Stack;
                     Initial_Size : in Size_Type := Max_Size);
   procedure Push (Into : in out Stack; Element : in Element_Type);
   procedure Pop (From : in out Stack; Element : out Element_Type);
   Overflow : exception;
   Underflow : exception;
private
   subtype Index_Type is Size_Type range 1 .. Max_Size;
   type Vector is array (Index_Type range <>) of Element_Type;
   type Stack (Allocated_Size : Size_Type := 0) is record
      Top : Index_Type;
      Storage : Vector (1 .. Allocated_Size);
   end record;
end Stacks;
Pointers
Case Sensitivity X
Semantic Indentation X
MultiLine Comments X

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