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Resolve "Break 020_declarations into chapters"
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‎courses/fundamentals_of_ada/020_declarations.rst

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‎courses/fundamentals_of_ada/020_declarations/01-introduction.rst

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==============
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Introduction
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==============
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----------------
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Ada Type Model
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----------------
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* Each :dfn:`object` is associated a :dfn:`type`
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* **Static** Typing
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- Object type **cannot change**
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- ... but run-time polymorphism available (OOP)
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* **Strong** Typing
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- **Compiler-enforced** operations and values
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- **Explicit** conversions for "related" types
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- **Unchecked** conversions possible
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* Predefined types
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* Application-specific types
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- User-defined
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- Checked at compilation and run-time
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------------
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Declarations
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------------
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* :dfn:`Declaration` associates a :dfn:`name` to an :dfn:`entity`
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- Objects
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- Types
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- Subprograms
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- et cetera
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* In a :dfn:`declarative part`
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* Example: :ada:`N : Type := Value;`
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- ``N`` is usually an :dfn:`identifier`
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* Declaration **must precede** use
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* **Some** implicit declarations
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- **Standard** types and operations
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- **Implementation**-defined
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‎courses/fundamentals_of_ada/020_declarations/02-identifiers_and_comments.rst

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==========================
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Identifiers and Comments
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==========================
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-----------
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Identifiers
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-----------
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.. image:: identifier_flow.png
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:width: 60%
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.. container:: columns
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.. container:: column
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* Legal identifiers
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.. code:: Ada
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Phase2
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A
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Space_Person
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.. container:: column
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* Not legal identifiers
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.. code:: Ada
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Phase2__1
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A_
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_space_person
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* Character set **Unicode** 4.0
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* Case **not significant**
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- `SpacePerson` |equivalent| `SPACEPERSON`
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- ...but **different** from `Space_Person`
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* Reserved words are **forbidden**
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----------------
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Reserved Words
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----------------
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.. code:: Ada
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abort else null reverse
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abs elsif of select
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abstract (95) end or separate
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accept entry others some (2012)
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access exception out subtype
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aliased (95) exit overriding (2005) synchronized (2005)
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all for package tagged (95)
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and function parallel (2022) task
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array generic pragma terminate
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at goto private then
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begin if procedure type
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body in protected (95) until (95)
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case interface (2005) raise use
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constant is range when
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declare limited record while
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delay loop rem with
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delta mod renames xor
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digits new requeue (95)
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do not return
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----------
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Comments
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----------
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* Terminate at end of line (i.e., no comment terminator sequence)
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.. code:: Ada
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-- This is a multi-
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-- line comment
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A : B; -- this is an end-of-line comment
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----------------------------------------------
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Declaring Constants / Variables (simplified)
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----------------------------------------------
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* An :dfn:`expression` is a piece of Ada code that returns a **value**.
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.. code:: Ada
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<identifier> : constant := <expression>;
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<identifier> : <type> := <expression>;
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<identifier> : constant <type> := <expression>;
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------
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Quiz
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------
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Which statement(s) is (are) legal?
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A. ``Function : constant := 1;``
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B. :answermono:`Fun_ction : constant := 1;`
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C. ``Fun_ction : constant := --initial value-- 1;``
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D. ``Integer Fun_ction;``
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.. container:: animate
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Explanations
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A. :ada:`function` is a reserved word
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B. Correct
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C. Cannot have inline comments
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D. C-style declaration not allowed
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‎courses/fundamentals_of_ada/020_declarations/03-literals.rst

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==========
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Literals
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==========
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-----------------
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String Literals
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-----------------
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* A :dfn:`literal` is a *textual* representation of a value in the code
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.. code:: Ada
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A_Null_String : constant String := "";
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-- two double quotes with nothing inside
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String_Of_Length_One : constant String := "A";
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Embedded_Single_Quotes : constant String
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:= "Embedded 'single' quotes";
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Embedded_Double_Quotes : constant String
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:= "Embedded ""double"" quotes";
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.. container:: speakernote
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Note that the last example literal (that has embedded double quotes) is not an example of concatenation!
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--------------------------
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Decimal Numeric Literals
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--------------------------
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* Syntax
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.. code::
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decimal_literal ::=
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numeral [.numeral] E [+numeral|-numeral]
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numeral ::= digit {['_'] digit}
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* Underscore is not significant
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* **E** (exponent) must always be integer
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* Examples
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.. code:: Ada
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12 0 1E6 123_456
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12.0 0.0 3.14159_26 2.3E-4
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------------------------
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Based Numeric Literals
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------------------------
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.. code::
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based_literal ::= base # numeral [.numeral] # exponent
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numeral ::= base_digit { '_' base_digit }
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* Base can be 2 .. 16
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* Exponent is always a base 10 integer
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::
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16#FFF# => 4095
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2#1111_1111_1111# => 4095 -- With underline
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16#F.FF#E+2 => 4095.0
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8#10#E+3 => 4096 (8 * 8**3)
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--------------------------------------------
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Comparison to C's Based Literals
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--------------------------------------------
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* Design in reaction to C issues
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* C has **limited** bases support
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- Bases 8, 10, 16
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- No base 2 in standard
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* Zero-prefixed octal :code:`0nnn`
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- **Hard** to read
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- **Error-prone**
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------
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Quiz
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------
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Which statement(s) is (are) legal?
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A. :answermono:`I : constant := 0_1_2_3_4;`
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B. ``F : constant := 12.;``
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C. ``I : constant := 8#77#E+1.0;``
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D. ``F : constant := 2#1111;``
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.. container:: animate
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Explanations
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A. Underscores are not significant - they can be anywhere (except first and last character, or next to another underscore)
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B. Must have digits on both sides of decimal
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C. Exponents must be integers
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D. Missing closing \#
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