.Open The Syntax of PHP
This page was created by Paul Conrad as part of his Graduate
Independent Study (CSCI695) of the syntax and semantics of the PHP
language.

This page describes the syntax of the PHP programming language based on
the definitions of the language in Programming PHP by Rasmus Lerdorf, and 
Kevin Tatroe, published by O'Reilly Publishing.  Since PHP is still a
rapidly evolving programming language, the syntax presented here is for
PHP 4.

. See Also

For a quick, concise reference to terms used through out this page, see 
.See ./php.glossary.html
which contains meta-linguistic terms, lexemes, and keyword definitions based on
the C++ glossary found at
.See http://www.csci.csusb.edu/dick/samples/c++.glossary.html
with the appropriate adaptations to PHP.

. PHP Comments

Commenting code in PHP can be achieved in three different styles.  The first
two styles are the C/C++ style of comments, and the third commenting style 
used in PHP is the Shell style comments.  These three styles of commenting
are quite universal through out computer science.  C/C++/Java programmers, and
Unix Shell programmers do not have to learn a new style of commenting in order
to comment PHP code.  This allows these programmers to comment PHP with a 
comment style they are most familiar or comfortable with. 

comments::=C_C++.comment|Shell.comment.

C_C++_comment::=C.comment|C++.comment.

C.comment::="/*" string_with_no_end_comment) "*/".

C comment containing all characters for comments except for the terminating */.

C++.comment::="//" O(the_comment) eol.

Shell.comment::="#" O(the_comment) eol.

string_with_no_end_comment::= #char ~(#char "*/" #char).

the_comment::=#(non(eol)).

This is the string of all no $eol characters in the comments.

eol::=`end of line character`.

For various styles of comments in PHP, see 
.See ./php.samples.html#PHP comments
.

Note:  Just as a quick point, the HTML code generated by PHP will not contain
the comments.  The comments are only on the server side for the programmer, so
do feel free to comment the code for better readability and do not concern
having comments affect the bandwidth or time it takes to load the generated
HTML.

. PHP Lexemes

keyword::=See
.See ./php.glossary.html#core_keyword
punctuation::=To Be Done.
operators::=see
.See PHP Expressions and Operators
below.
identifier::=See
.See PHP Identifiers
next.

. PHP Identifiers

. Variables

variable_declaration::=O("static") "$" O("$") $identifier_name,

identifier_name::=( letter | underscore ) #( letter | digit | underscore | extended_ascii ),

extended_ascii::=char_nbr(127)..char_nbr(255),

For the definitions of letter, underscore, and digit, see
.See http://www.csci.csusb.edu/dick/maths/intro_ebnf.html#Lexemes
for details.

Note:  PHP allows for the use of ASCII codes from 0x7F (127) to 0xFF (255)
for valid characters to begin an identifier with.  To represent the i'th
ASCII character, the notation char_nbr(i) is used.

For various examples of variables in PHP, see 
.See ./php.samples.html#PHP variables
.

. Functions

function_declaration::= O("&") ignore_case( $function_name ) "(" parameter #( , parameter ) ) "{" $statement "}",

parameter::="$" identifier_name,

anonymous_function::= create_function( $argument_string, $code_string ),

Note:  Anonymous functions are like LISP lambda expressions.  They are functions created
on the fly inside an expression.  The result can be assigned to a variable or passed as a
parameter.

See the examples on using anonymous functions at
.See ./php.samples.html#anonymous_functions
.

function_name::= "$" identifier_name,

For ignore_case, see
.See http://www.csci.csusb.edu/dick/samples/comp.text.ASCII.html#ignore_case 
for more details.

See function semantics at 
.See ./php.semantics.html#functions 
for more details.

For various examples of functions in PHP, see 
.See ./php.samples.html#PHP functions
.

. Classes

class_definition::= "class" $class_name O( "extends" $class_name ) "{" $class_body "}",

class_name::=$identifier_name,

class_body::= #( $variable_declaration | $function_declaration ),

The class name "stdClass" is reserved and cannot be used as an identifier for a class.

Note:  In PHP, there is no concept of private, public, or protected member functions or properties.

For a class example, see 
.See ./php.samples.html#PHP classes
.

. Constants

define::="define( O(') $identifier_name O('), "$constant_value", O( $case_sensitive ) )",

case_sensitive::= ( true | false ),

constant_value::=( boolean | integer | double | string ) ~(quotation_mark),

quotation_mark::=""" | character_nbr(34).

For examples of constants, see
.See ./php.samples.html#PHP constants
.

. PHP Data Types

. Scalar Types 

integer::=( O("+") | - ) digit #digit,

In PHP the range of integers is between -2147483648 and 2147483647.  An interesting 
note about PHP and integers, when the value assigned goes outside these minimum/maximum
boundaries, the value is automatically converted to floating point.
 
floating_point::=( O("+") | - ) digit "." digit #digit O( "E" integer ),

In PHP if a variable is assigned a value 7 or 7., echoing to the browser will display 7.

string::=( single_quote_string | double_quote_string | heredoc ),

double_quote_string::=quotation_mark (#char(~quotation_mark) | #escape_seq) quotation_mark,

escape_seq::= "\"" | "\n" | "\r" | "\t" | "\\" | "\$" | "\{" | "\}" | "\[" | "\]" | ascii_octal | ascii_hex,

ascii_octal::= "\0".."\777",

ascii_hex::= "\x0".."\xFF',

single_quote_string::="'" #char(~"'") "'",

heredoc::= "$"$identifer_name " = <<<" $sentinel #(line~sentinel) $sentinel";",

sentinel::= $identifier_name,

line::= #(char~eol) eol,

Note:  The sentinel must be the same on both sides, opening and closing the heredoc.

boolean::=ignore_case( TRUE | FALSE ),

. Compound Data Types

For arrays and objects, see 
.See ./php.misc.html#compound_types
.

. PHP Special Types

NULL::=ignore_case("NULL"), nullifies the value of a variable,

This special type is used to represent a variable that does not contain any value, and
is similar to undef in Perl and 'None' in Python.

The predefined PHP function, is_null() allows for testing whether or not a variable 
holds a NULL value or not.

For the PHP special type, resource, see 
.See ./php.misc.html#resource_type
.
 
. PHP Expressions and Operators

.Table Operator_Precedence	Associativity	Operator	Operation
.Row 19	Non Associative	new	Creates a new object
.Row 18	Right Associative	[	Array subscript
.Row 17	Right Associative	!	Logical NOT
.Row 17	Right Associative	~	Bitwise NOT
.Row 17	Right Associative	++	Increment
.Row 17	Right Associative	--	Decrement
.Row 17	Right Associative	(int),(double),(string),(array),(object)	Cast type
.Row 17	Right Associative	@	Inhibit error reporting
.Row 16	Left Associative	*	Multiplication
.Row 16	Left Associative	/	Division
.Row 16	Left Associative	%	Modulus
.Row 15	Left Associative	+	Addition
.Row 15	Left Associative	-	Subtraction
.Row 15	Left Associative	.	String concatenation
.Row 14	Left Associative	<<	Bitwise SHIFT LEFT
.Row 14	Left Associative	>>	Bitwise SHIFT RIGHT
.Row 13	Non Associative	<,<=	Less Than, Less Than or Equal To
.Row 13	Non Associative	>,>=	Greater Than, Greater Than or Equal To
.Row 12	Non Associative	==	Value Equality
.Row 12	Non Associative	!=,<>	Value Inequality
.Row 12	Non Associative	===	Type and Value Equality
.Row 12	Non Associative	!==	Type and Value Inequality
.Row 11	Left Associative	&	Bitwise AND
.Row 10	Left Associative	^	Bitwise XOR
.Row  9	Left Associative	|	Bitwise OR
.Row  8	Left Associative	&&	Logical AND
.Row  7	Left Associative	||	Logical OR
.Row  6	Left Associative	?:	Conditional Operator
.Row  5	Left Associative	=	Assignment Operator
.Row  5	Left Associative	+=,-=,*=,/=,.=,%=,&=,|=,^=,~=,<<=,>>=	Assignment with Operation
.Row  4	Left Associative	and	Logical AND
.Row  3	Left Associative	xor	Logical XOR
.Row  2	Left Associative	or	Logical OR
.Row  1	Left Associative	,	List separation
.Close.Table

S(E,Op)::=$serial_operator_expression(E, Op)

serial_operator_expression(E,Op)::= E #(Op E).
.As_is 		S(E,Op) = E Op E Op E Op ... E

. Arithmetic Operations

post_fix::="++" | "--",

post_fix_expression::=($primary_expression) #($post_fix),

unary_operator::="&" | "*" | "+" | "-" | "!" | "-",

pre_fix::="++" | "--" | "sizeof",

unary_expression::=#($pre-$fix) $post_fix_expression | $unary_operator $variable_name,

multiplicative_expression::=$S($cast_expression, $multiplicative_operator).
.See serial_operator_expression

The rule above means that 'casts' are done before multiplication and division, and that multiplication and division are done from left to right.

multiplicative_operator::="*" | "%" | "/",

additive_expression::=$S($multiplicative_expression, $additive_operator).
This means that addition and subtraction occurs after multiplication and from left to right.

additive_operator::="+" | "-",

. Shift Operations
shift_expression::=$S($additive_expression, $shift_operator),

shift_operator::=">>" | "<<",  "<<" is left shift of bits (multiply by 2),
and ">>" is the reverse and divides by 2.

. Relation Operations
relational_expression::= $S($shift_expression, $relational_operator),

relational_operator::="<" | ">" | "<=" | ">=",

equality_expression::=$S($relational_expression, $equality_operator),

equality_operator::="==" | "!=",

. Bitwise Expressions
AND_expression::=$S($equality_expression, $and_operator),

and_operator::="&"
,
XOR_expression::=$S($AND_expression, $XOR_operator),

XOR_operator::="^",

OR_expression::=$S($XOR_expression, $OR_operator),

OR_operator::="|",

. Logical Expressions

logical_AND_expression::=$S($XOR_expression, $logical_AND_operator),

logical_AND_operator::="&&" | "and",

logical_XOR_expression::=$S($logical_OR_expression, $logical_XOR_operator),

logical_XOR_operator::="xor",

logical_OR_expression::=$S($logical_XOR_expression, $logical_OR_operator),

logical_OR_operator::="||" | "or",

. Conditional Expressions
conditional_expression::=$logical_OR_expression | $logical_OR_expression "?" $expression ":" $conditional_expression,

. Assignment Statements
assignment_expression::=$S($unary_expression, $assignment_operator),

assignment_operator::="=" | "*=" | "/=" | "%=" | "+=" | "<<=" | ">>=" | "&=" | "^=" | "|=",

expression::=$List($assignment_expression ),

constant_expression::=$conditional_expression,

. Casting Operators

Even though PHP is a weak typed language, there are ways to specify a type for a variable.  We have the following casting operators:

cast_expression::= $integer | $float | $string | $boolean,

integer::= ( "(int)" | "(integer)" ) O( $unary_expression) $variable,

float::= ( "(float)" | "(real)" ) O( $unary_expression) $variable,

string::= "(string)" O( $unary_expression) $variable,

boolean::= ( "(bool)" | "(boolean)" ) O( $unary_expression) $variable,

. Compound Data Types

array::= "(array)" $variable,

object::= "(object)" $variable.

. Miscellaneous Operators

error_suppression::= "@",

execution::="`" command_string "`",

command_string::=#char,

conditional::= expression "?" true_expression ":" false_expression,

true_expression::= `Expression to be evaluated when conditional is true`,

false_expression::= `Expression to be evaluated when conditional is false`,

. Statements

statement::= $compound_statement | $expression_statement | $switch_statement | $iteration_statement | $for_statement | $foreach_statement | $if_statement | $labeled_statement | $declare_statement | $exit_or_return

block_statement::= "{" #($statement ";") "}",

compound_statement::=#($statement ";"),

. Flow Control Statements

if_statement::= "if (" $expression ")" $statement | "if (" $expression ")" $statement " else " $statement | "if (" $expression ") {" $compound_statement "} else {" $compound_statement "}" | "if (" $expression ") : " $compound_statement O( "else: " $compound_statement ) "endif;",

switch_statement::= "switch (" $expression ") { " $compound_statement "}" | "switch (" $expression ") : " $compound_statement "endswitch;",

iteration_statement::= "while (" $expression ") $statement | "while (" $expression ") { " $compound_statement " } " | "while (" $expression ") : " $compound_statement " endwhile;" | "do " $compound_statement "while (" $expression ");",

for_statement::= "for (" O( $expression ) ";" O( $expression ) ";" O( $expression ) ")" ( $statement | $block_statement ),

foreach_statement::= "foreach (" $array " in " ( $current_value | $key => $current_value ) ") ( $statement | "{ $compound_statement }" ),

current_value::= $identifier_name,

key::= $array_key,

For information on array key see 
.See ./php.misc.html#array_keys
.

declare_statement::= "declare ( $directive ) { $compound_statement }",

directive::= "ticks = " number_ticks,

number_ticks::= #digits,

See notes on the declare function for more information at 
.See ./php.misc.html
.

exit_or_return::= ( "exit" $O( $expression ) | "return" $O( $expression ) ),

labeled_statement::="case " $constant_expression ":" $statement | "default: " $statement,

. Including Code

. Posix Regular Expressions

.Table Posix_Character_Classes	RegExpressions
.Row [:alnum:]	[0-9a-zA-Z]
.Row [:alpha:]	[a-zA-Z]
.Row [:ascii:]	[\x01-\x7F]
.Row [:blank:]	[ \t]
.Row [:cntrl:]	[\x01-\x1F]
.Row [:digit:]	[0-9]
.Row [:graph:]	[^\x01-^\x20]
.Row [:lower:]	[a-z]
.Row [:print:]	[\t\x20-\xFF]
.Row [:punct:]	[-!"#$%&'()*+,./:;<=>?@[\\]^_`{|}~]
.Row [:space:]	[\n\r\t \x0B]
.Row [:upper:]	[A-Z]
.Row [:xdigit:]	[0-9a-fA-F]
.Close.Table

start_word::= "[[:<:]]",

end_word::= "[[:>:]]",

posix_reg_expression_functions::= $matching | $replacing | $split,

matching::= ( "ereg" | "eregi" )( $pattern, $target_string, O( $captured ) ),

Note:  eregi is just the case-insensitive form of ereg.

pattern::= $O($at_start) #( ($wildcard | $special | $start_word | $end_word ) $O("*") ) $O($at_end),

at_start::="^",

at_end::="$",

wildcard::= "." | "[" $O($not_operator) #$set_of_character "]",

not_operator::="^",
    
set_of_character::= char | char "-" char

target_string::= $string, this string contains the text to search,

replacing::= ( "ereg_replace" | "eregi_replace" )( $pattern, $replacement, $string ),

$replacement::=expression,

$string::=expression,

Note:  eregi_replace is just the case-insensitive form of ereg_replace.

split::= split($pattern, $string, O( $limit ) ),

. Perl Regular Expressions

Please visit 
.See ./php.misc.html#perl_regex_todo
.

.Close The Syntax of PHP