Tekst źródłowy strony Axiomatic definition of Loglan'82

On these pages we are sketching, in an incremental way, an axiomatic semantics of Loglan'82.<br />
'''
Axiomatic definitions of sublanguages of Loglan'82''' <br />

Here we shall present an increasing sequence of sublanguages <math>\mathcal{L}_0\subset\mathcal{L}_1\subset\mathcal{L}_2\subset \mathcal{L}_3\subset\mathcal{L}_4\subset \dots</math>Loglan'82. For each language <math>\mathcal{L}_i</math> we shall present its grammar and some axioms and inference rules that define its  semantics. 
== Program ==
Program in Loglan'82 has the following structure<br />

{| class="wikitable"
|+ Program
!definiendum!! definiens
|-
| style="background-color:palegreen" | ''program''
| style="background-color:GoldenRod" | '''program''' <''name''>;<br />

:<''declarations''><br />

'''begin'''<br />

:<''instructions''><br />

'''end'''
 
|}

where ''name'' is any identifier, i.e. a finite sequence of letters and digits beginning with a letter.

The ''declarations'' and ''instructions'' are  finite sequences of declarations and instructions respectively, empty squence included.

This allow us to define the first sublanguage <math>\mathcal{L}_{0,0}</math> of Loglan'82.
=== Language <math>\mathcal{L}_{0,0}</math> ===
<math>\mathcal{L}_{0,0} \stackrel{df}{=}\{p\in \mathcal{A}^*: p=\textbf{program}\ \textit{id}; \textbf{begin end}  \}</math>

Programs of the language <math>\mathcal{L}_{0,0}</math> are empty programs, they posses just a name. Their list of instructions as well as list of declarations are empty. The effect of execution of such program is ''do nothing''.
=== Language <math>\mathcal{L}_{0,1}</math> ===
Now we shall define a new language <math>\mathcal{L}_{0.1}</math>. First, we say that any expression of the form:<br />
writeln;  <br /> 
write(''integer''); <br />
write("here your text"); <br />
is an output instruction.

<math>\mathcal{L}_{0.1} \stackrel{df}{=}\{p\in \mathcal{A}^*: p=\textbf{program} \textit{ id}; \textbf{begin} <\textit{output instructions}> \textbf{end}  \}</math>

 

where ''name'' is any identifier, i.e. a finite sequence of letters and digits beginning with a letter.

The ''declarations'' and ''instructions'' are  finite sequences of declarations and instructions respectively, empty squence included.

'''Example 0.1''' <br />
{| class="wikitable"
|-  
|style="background-color:#FFCC99" | program print; <br />
begin <br />
:write("hallo world!"); writeln; <br />
:write("Today is: May"); write(22); write(2014); writeln <br />
end <br/>
|}
Semantics

Each output instruction appends a string of characters to the standard output.

== <math>\mathcal{L}_{1}</math> Declarations of variables. Assignment instructions ==
Now we shall introduce the linear programs. Each program of this group contains declarations of variable and the instructions of a program are the assignment instructions only.<br />
The language <math>\mathcal{L}_{1}</math> is the closure of languages   <math>\mathcal{L}_{1,c} \cup \mathcal{L}_{1,s}\cup \mathcal{L}_{1,b}\cup \mathcal{L}_{1,i}\cup \mathcal{L}_{1,r}</math>
The structure of a program is as follow:
{| class="wikitable"
|+ Program
!definiendum!! definiens
|-
| style="background-color:palegreen" | ''program''
| style="background-color:GoldenRod" | '''program''' <''name''>;<br />
:<''declarations of variables''><br />
'''begin'''<br />
:<''instructions''> i.e.<br />
:: sequence of <br />
::<''output instructions'' or ''assignment instructions'' >
'''end'''
|}

where ''name'' is any identifier, i.e. a finite sequence of letters and digits beginning with a letter.

The ''declarations'' and ''instructions'' are  finite sequences of declarations and instructions respectively, empty squence included.
The structure of assignment instruction is 
<math> variable := expression </math>
An assignment instruction is well formed if the types of the variable and of expression are equal and if all variables are declared in the program.

Axioms<br />

{| class="wikitable"
|+ Axiom of assignment instruction
|-
| style="color:Blue" | <math> \qquad\qquad \{x:=\tau\}( \alpha ) \equiv \alpha(x/\tau) \qquad \qquad </math> 
|}


{| class="wikitable"
|+ Axiom of composed instruction
|-
| style="color:Blue" | <math>  \textbf{begin }\, K: M \textbf{ end}\, \alpha \equiv K M\, \alpha  </math>
|}
How to use these axioms?<br />
We present a lemma that is universally true for all the sublanguages of the language <math>\mathcal{L}_{1}</math>.<br />
{| class="wikitable"
|- 
| style="background-color:palegreen" | 
|'''Lemma''' <br />
Let <math> T </math> be a type. Let <math>x, y, z</math> be variables of type <math>T</math>. The following algorithmic formula is tautology
<math> (x=a \land y=b)\implies \{z:=x;\,x:=y;\,y:=z \}(x=b \land y=a) </math> <br />
'''Proof'''. By the axiom of composed instruction and propositional calculus our formula<br />
<math> (x=a \land y=b) \implies \{\underbrace{z:=x;\, x:=y;}_{K}\,
  \underbrace{y:=z}_{M}\}\underbrace{(x=b \land y=a)}_{\alpha} </math> <br /> 
is equivalent to <br />
<math> (x=a \land y=b) \implies \overbrace{\{z:=x;\, x:=y\}}^{K} \overbrace{\underbrace{\{
  y:=z\}}_{y:=z}}^{M}\underbrace{(x=b \land y=a)}_{\alpha(y)} </math> <br />
Using the axiom of assignment instruction we get an equivalent formula <br />
<math> (x=a \land y=b)\implies \{z:=x;\,x:=y;\}\underbrace{(x=b \land z=a)}_{\alpha(y/z)} </math> <br />
Again the axiom of composed instruction <br />
<math> (x=a \land y=b)\implies \{z:=x\} \{x:=y;\}(x=b \land z=a) </math> <br />
Now, by applying twice the axiom of assignment instruction we get<br />
<math> (x=a \land y=b)\implies \{z:=x\} (y=b \land z=a) </math> <br />
and <br />
<math> (x=a \land y=b)\implies (y=b \land x=a) </math> <br />
The last formula is tautology. All formulas are equivalent. Hence, our first formula is proved.
|}
-----
Note, the meaning of the lemma is ''if initially the value of x is a and the value of y is b, then after execution of these three instructions the variables swapped their values x=b and y=a ''
=== Language <math>\mathcal{L}_{1,c}</math> ===
Declarations are declarations of variables of type char.
Type '''char''' is a finite set of characters. Obviously it contains all letters, digits and delimiters.There are no operations on characters and the only relation in this set is the identity relation =.

Consequently the only characters expressions are character constants and character variables.
 
'''Example'''<br />
{| class="wikitable"
|-  
|style="background-color:#FFCC99" | '''program''' print; <br />
:'''var''' x: char;<br />
:'''var''' y,z: char
'''begin''' <br />
:x := 'a'; <br />
:y := x;<br />
:write("Today is: May"); write(22); write(x,'d'); writeln <br />
'''end''' <br/>
|}
Axioms of data structure (type) '''char'''.
{| class="wikitable"
|+ Axiom enumerating the type char
|-
| style="color:Blue" | <math>  \forall_{x \in char}(x=’a’\lor \dots \lor x=’z’ \lor x='A' \lor \dots x='Z' \lor \dots) </math> 
|}
The reader is kindly requested to complete the above line.

{| class="wikitable"
|+ Axioms of identitities of char constants
|-
| style="color:Blue" | <math>  (('a'\neq\, 'b') \land ('a'\neq\, 'c')\land \dots )  </math>
|}
Also this line can be completed without problems.
-----

=== Language <math>\mathcal{L}_{1,s}</math> ===
Declarations are declarations of variables of type string.
Type '''string''' is an infinite set of finite words over the alfabet of characters.  There are no operations on strings and the only relation ...

Consequently the only string expressions are string constants and string variables.
 
'''Example'''<br />

program Strings;
   var x,y: string;
begin
   x := 'ba';
   y := x
end
-----
=== Language <math>\mathcal{L}_{1,b}</math> ===
Declarations are declarations of variables of type boolean.
Type '''char''' is a finite set of characters. Obviously it contains all letters, digits and delimiters.There are no operations on characters and the only relation in this set is the identity relation =.

Consequently the only characters expressions are charcter constants and character variables.
 
'''Example'''<br />

program Booleans;
   var x,y: boolean;
begin
   x := 'false';
   y := x OR 
end
-----

'''Example'''<br />

'''program'''  P2 ;<br />
:'''var''' x,y: integer;<br />
'''begin'''<br />
:y:=74;<br />
:x:= y+ 8;<br />
'''end'''<br />

'''Grammar'''<br />
'''program''' <name>;
:'''var''' id: char; '''var''' id1: char;
'''begin'''
:id1 := character expression;
:id :=character expression
'''end'''

Context free grammar
character expression ::= character constant | character variable
character constant ::= 'a'| ... |'z'|'A'| ... |'Z'|'+'|'&'| ...
character variable :: 
Well formed expressions
:A character expression <mat>\tau</math> occurring in a program <math>P</math>, is well formed iff either it is a character constant or it is a variable declared in the program.

'''Axiom'''<br />

<math>\{x:=\tau\}( \alpha ) \Leftrightarrow \alpha(x/\tau)</math>

== <math>\mathcal{L}_{2}</math> Conditional instructions ==
== <math>\mathcal{L}_{3}</math> Arrays and '''for''' instructions ==
== <math>\mathcal{L}_{4}</math> Iteration instructions ==