Ada

General

File extension:
- Source file: .adb
- Specification file: .ads (like mli file in ocaml)
Attributes of a name are accessed using ' (called a 'tick')
- Eg: Integer'size
Ada is case insensitive.
- Even for variable names.
- Explains why keywords (but not variable names) in vhdl are case insensitive..
Comments: starts with --
- No way to make multi-line comments.
- This is intentional to avoid problems with nested comments.
Functions are called 'subprograms'
Apparently, we can't control variance of subtypes in ada.
Strong typing
- Got to give a type to everything
- No type inference ??
  - Quite verbose as a result ??
- No implicit type conversion
  - Type casts are there though.
  - See where VHDL gets it from? 😃
SPARK
- A subset of ada
- Testing and verification is easier in this??
ARM: Ada reference manual
- An ISO standard, that is free. Unlike that of C++.
GNAT: ada compiler that is part of gcc
gnatmake: basic build manager
gprbuild: gnat project manager
Alire: a package manager for ada
Community: https://groups.google.com/g/comp.lang.ada/ (looks unmoderated though..)
Emacs mode: https://www.gnu.org/software/emacs/manual/html_mono/ada-mode.html
limited: makes assignment to declared variable impossible
- Kind of like const in cpp.

with Ada.Text_IO;
use Ada.Text_IO;

procedure Hello is begin
  Put_Line ("Hello world!");
end Hello;

Convert a value to string and vice-versa.

declare
  X : Integer := 10;
begin
  -- "10"
  Put_Line (Integer'Image (X));

  -- 20
  X := Integer'Value ("20");
end;

-- A new type. Like {x: Integer | x ∈ [0,23]}
type Hours24  is new Integer range 0 .. 23;

-- A subtype
subtype Hours is Hours24 range 0 .. 11;

-- a char array of size 10
Name : array (0 .. 9) of Character;

type Day is
  (Mon,
   Tue,
   Wed,
   Thu,
   Fri,
   Sat,
   Sun);

Representation clause ?? can be used if needed:

for Day use
  (Mon => 10,
   Tue => 11,
   Wed => 12,
   Thu => 13,
   Fri => 14,
   Sat => 15,
   Sun => 16);

Used to be used in defense application in US and Europe earlier
- Used to mandatory for defense contractors
Named after Ada Lovelace.
Introduced many PL-related concepts
- Influenced design of many languages which are now popular
- Though ada itself never found popularity outside of a very niche world
ghdl has a lot of ada code
- One of the few projects that still has significant ada