.Open Small Awk
. Status
THis is a first draft for a new language.  The symbol $TBD
indicates a known area of incompleteness "To Be Done".
. Purpose
Small Awk (not $smalltalk!)
is designed as sample language studied and worked on in
Computer Science classes that study high level computer languages.
It is a subset of the $awk language of Aho, Weinberg and Kernighan.
IT is a subset created by deleting a lot of useful convenient options
and features for $awk.  Even so it is a languages that has control structures
variables, input, and output.  For simple, every day programs it is
rather like a small and safe C or C++.

Small awk programs can be tested by running them thru any $awk
interpreter on a UNIX system.  $awk has also been ported to other
platforms and can also be used to test smallawk programs.  Suppose your
smallawk program is in a file called
.As_is 		hello.awk
then the command
.As_is 		awk -f hello.awk
will test the program.

Like $awk, smallawk is designed for processing data files.  It works with
simpler files than $awk however.  Smallawk assumes that it will read
a single file and each line in the file is a list of "fields" of data
separated by one or more spaces or tabs.   Smallawk reads the inoput file 
and produces a
single stream of output by processing the input.  Notice that a smallawk
program does not start until it is given some data, and doesn't stop
until it gets the usual end-of-file.  Here is a traditional simple
program in smallawk:
.As_is 		END{ print "hello, world"; }
It reads the input and at the end of the inpoyut data it outputs the
"hello, world message.  The following program reads the input file
and numbers the lines:
.As_is 		{ print NR, $0; }

The next program prints outs lines that contain the string "AWK":
.As_is 		/AWK/{ print ;}

The next program Assumes that each line has one number, and at the
end of the file outputs the total of these nunmbers:
.As_is 		{sum = sum + $0;}
.As_is 		END{print sum;}

This one checks the input and only adds a line if it is a valid integer,
with one or more decimal digits:
.As_is 		/^[0-9][0-9]*$/{sum = sum + $0;}
.As_is 		END{print sum;}

This reads in a file of names, student_ids, and scores
and calculates the mean score.  It assume input  with data
separated by spaces like this:
.As_is ShortName 9999 3.2
.As_is AnotherName 1234 17
The program is
.As_is 		{sum = sum + $3; count=count+1;}
.As_is 		END{print sum/count;}


.Open Syntax
. Lexemes
smallawk has the normal lexical scan separating variables, constants,
strings, from some reserved words:
reserved_words::= "END" | "NF" | "NR" | "BEGIN" | "print" | "if" | "else".

comma::=",".
. Programs
A program is a sequence of pieces.  Each piece has two parts:
a pattern and an action.  The pattern states when the action is to be applied.
When smallawk is running it takes each line and tries each piece of the program
in turn and carries out the actions with patterns that match the line.

program::= # $piece.

piece::= $O( $pattern ) "{" $action "}".
The pattern is used to recognise the lines of data
that the action applies to.
. Patterns

disjunction::= $conjunction #( "||" $conjunction).
.As_is 		/Botting/||/Dick/
conjunction::= $possible_complement #( "&&" $possible_complement).
.As_is 		/Botting/ && /Richard/
possible_complement::= "!" $elementary_pattern | $elementary_pattern.
.As_is 		!/Blotting/

elementary_pattern ::=  "END" | "BEGIN" | "/" $regular_expression "/".
.As_is 		/Banana/
.As_is 		/[bB]anana/
.As_is 		/^\.As_is/
.As_is 		/^[0-9]*$/

regular_expression::= $left_most | $rightmost | $exact | $contained.

leftmost::= "^" $contained.
.As_is 		^.As_is
rightmost::= $contained "$".
.As_is 		two part:$
exact::= "^" $contained "$".
.As_is 		^Dick.*Botting$

contained::= #possibly_repeated_set_of_chars.

possibly_repeated_set_of_chars::= $possible_set "*" | $possible_set.
.As_is 		pos*ibil*ity
The "*" means "zero or more of".
The above matches "posssibiity" for example.

possible_set::=$normal_character | $escaped_character | $set_of_characters.

normal_character::= letter | digit | symbol ~ $special_character.
escaped_character::= "\" $special_character.
special_character::= "[" | "]" | "\" | "." | "*".
set_of_characters::= "[" chars "]" | "[^" chars "]".
chars ::= # character |  character "-" character.
character::= normal_character | escaped_character.

. Actions
An action is a series of at least one statement.  These are
executed one after another.
action::= $statement #$statement.
. Statements
statement::= $assignment | $print | $selection | $do_nothing.

assignment::= $variable "=" $expression ";"
.As_is 		sum = sum + $0;

print::= "print" ";"| "print" $expression ";".
.As_is 		print sum;

selection::= "if(" $condition ")" $body "else" $else.
.As_is 		if ( sum > 0 ) print "greater"; else ;

condition::=$expression.
body::=$action | $do_nothing.
else::=$action | $do_nothing.

do_nothing::= ";".

. Expressions
operation::= "+" | "-" | "*" | "/" | "%" | "&&" | "||" | "!".
function::= "sin" | "cos" | "log" | "exp" | "sqrt".

expression::= $concatenation.
concatenation::= $arithmetic_expression #$arithmetic_expression.

arithemetic_expression::= simple_expression #(#$operation simple_expression).
simple_expression::= function_call | $variable | $constant | parentesized_expression.
parenthesized_expression::= "(" $expressison ")".
function_call ::= $function "(" expression #( $comma expression ).

$TBD : Operations, variables, functions....
. Variables
variable::= $whole_line | $field | $global_variable.
whole_line::= $dollar "0".
.As_is 		$0
field::= $dollar expression.
.As_is 		$5
global_variable::=letter #(letter|digit).
.As_is 		sum
. Constants

$TBD
.Close Syntax.

. Semantics

Here are the informal operational semantics of a smallawk program `P`.
`P` wll consist of a sequence of `n` pieces `p`[1]..`p`[`n`].
Each piece 'p'['i'] has two parts a pattern 'p'['i'].pattern
and an action 'p'['i'].action.

Here is a diagram:
	$TBD

Here is a C++like description of
what the program `P` does.
.As_is 
.As_is 	NR=1;
.As_is 
.As_is 	while( get next line until end of input )
.As_is 	{
.As_is 		for(i = 1; i<=n; i++)
.As_is 			if( line matches p[i].pattern )
.As_is 				apply p[i].action to line;
.As_is 
.As_is 		NR++;
.As_is	}
.As_is 
.As_is	//after end of file
.As_is 	for(i = 1; i<=n; i++)
.As_is 		if( p[i].pattern is "END" )
.As_is 			apply p[i].action;
.As_is 

A line matches a pattern according to the rules $TBD ...
.See http://www.csci.csusb.edu/dick/samples/regular_expressions.html

Applying an action to the line starts by assigning the whole line to
variable `$0`.  Then each field in the line (separated by one or more spaces)
is assigned to `$1` thru to `$NF` where `NF` is set to the number of fields.
An action is a sequence of one or more instructions and these are
executed in turn.  If an instruction is an assignment then the expression on
the right hand side is evaluated and the resulting value is placed in the
variable on the left hand side of the '=' sign.  This may change the whole
line or any field in the line if the variable is '$0' or '$i' for some other i.
If the action is a print command with an expression then the expression is evaluated and output plus a new line. If it is a print with no expression then
the whole line (with any changes) is printed.  If the instruction
is a selection with condition `c` and body `b` and else part 'e', then the condition is
evaluated and if it not zero the body `b` is executed. Other wise if `c` evaluates to zero then `e` is executed.

Expressions are evaluated in the usual way: constants beome their values,
variables return their current value, and operations are applied in order
of precedence to give a value.

. Authors
Richard J Botting
.See mailto:rbotting@csusb.edu

. See Also
awk::=http://www/dick/cs360/notes/awk.doc.html,
and some notes
.See http://www/dick/cs360/notes/awk.html.

smalltalk::=http://www/dick/samples/smalltalk.html
. Glossary
TBA::="To Be Announced".
TBD::="To Be Done".
For X, O(X) ::= (X | ), Optional X.
.Close Small Awk