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Last update Feb 25, 2003

Lexical

In D, the lexical analysis is independent of the syntax parsing and the semantic analysis. The lexical analyzer splits the source text up into tokens. The lexical grammar describes what those tokens are. The D lexical grammar is designed to be suitable for high speed scanning, it has a minimum of special case rules, there is only one phase of translation, and to make it easy to write a correct scanner for. The tokens are readilly recognizable by those familiar with C and C++.

Phases of Compilation

The process of compiling is divided into multiple phases. Each phase has no dependence on subsequent phases. For example, the scanner is not perturbed by the semantic analyser. This separation of the passes makes language tools like syntax directed editors relatively easy to produce.
  1. ascii/wide char
    The source file is checked to see if it is in ASCII or wide characters, and the appropriate scanner is loaded.
  2. lexical analysis
    The source file is divided up into a sequence of tokens. Pragmas are processed and removed.
  3. syntax analysis
    The sequence of tokens is parsed to form syntax trees.
  4. semantic analysis
    The syntax trees are traversed to declare variables, load symbol tables, assign types, and in general determine the meaning of the program.
  5. optimization
  6. code generation

Source Text

D source text can be in one of the following formats: Note that UTF-8 is a superset of traditional 7-bit ASCII. The source text is assumed to be in UTF-8, unless one of the following BOMs (Byte Order Marks) is present at the beginning of the source text:

Format BOM
UTF-8 EF BB BF
UTF-16BE FE FF
UTF-16LE FF FE
UTF-32BE 00 00 FE FF
UTF-32LE FF FE 00 00
UTF-8 none of the above

There are no digraphs or trigraphs in D. The source text is split into tokens using the maximal munch technique, i.e., the lexical analyzer tries to make the longest token it can. For example >> is a right shift token, not two greater than tokens.

End of File

	EndOfFile:
		physical end of the file
		\u0000
		\u001A
	
The source text is terminated by whichever comes first.

End of Line

	EndOfLine:
		\u000D
		\u000A
		\u000D \u000A
		EndOfFile
	
There is no backslash line splicing, nor are there any limits on the length of a line.

White Space

	WhiteSpace:
		Space
		Space WhiteSpace

	Space:
		\u0020
		\u0009
		\u000B
		\u000C
		EndOfLine
		Comment
	
White space is defined as a sequence of one or more of spaces, tabs, vertical tabs, form feeds, end of lines, or comments.

Comments

	Comment:
		/* Characters */
		// Characters EndOfLine
		/+ Characters +/
	
D has three kinds of comments:
  1. Block comments can span multiple lines, but do not nest.
  2. Line comments terminate at the end of the line.
  3. Nesting comments can span multiple lines and can nest.
Comments cannot be used as token concatenators, for example, abc/**/def is two tokens, abc and def, not one abcdef token.

Identifiers

	Identifier:
		IdentiferStart
		IdentiferStart IdentifierChars

	IdentifierChars:
		IdentiferChar
		IdentiferChar IdentifierChars

	IdentifierStart:
		_
		Letter

	IdentifierChar:
		IdentiferStart
		Digit
	
Identifiers start with a letter or _, and are followed by any number of letters, _ or digits. Identifiers can be arbitrarilly long, and are case sensitive. Identifiers starting with __ are reserved.

String Literals

	StringLiteral:
		SingleQuotedString
		DoubleQuotedString
		EscapeSequence

	SingleQuotedString:
		' SingleQuotedCharacters '

	SingleQuotedCharacter:
		Character
		EndOfLine

	DoubleQuotedString:
		" DoubleQuotedCharacters "

	DoubleQuotedCharacter:
		Character
		EscapeSequence
		EndOfLine

	EscapeSequence:
		\'
		\"
		\?
		\\
		\a
		\b
		\f
		\n
		\r
		\t
		\v
		\ EndOfFile
		\x HexDigit HexDigit
		\ OctalDigit
		\ OctalDigit OctalDigit
		\ OctalDigit OctalDigit OctalDigit
		\u HexDigit HexDigit HexDigit HexDigit
	
A string literal is either a double quoted string, a single quoted string, or an escape sequence.

Single quoted strings are enclosed by ''. All characters between the '' are part of the string except for EndOfLine which is regarded as a single \n character. There are no escape sequences inside '':

	'hello'
	'c:\root\foo.exe'
	'ab\n'			string is 4 characters, 'a', 'b', '\', 'n'
	
Double quoted strings are enclosed by "". Escape sequences can be embedded into them with the typical \ notation. EndOfLine is regarded as a single \n character.
	"hello"
	"c:\\root\\foo.exe"
	"ab\n"			string is 3 characters, 'a', 'b', and a linefeed
	"ab
	"			string is 3 characters, 'a', 'b', and a linefeed
	
Escape strings start with a \ and form an escape character sequence. Adjacent escape strings are concatenated:
	\n			the linefeed character
	\t			the tab character
	\"			the double quote character
	\012			octal
	\x1A			hex
	\u1234			wchar character
	\r\n			carriage return, line feed
	
Escape sequences not listed above are errors.

Adjacent strings are concatenated with the ~ operator, or by simple juxtaposition:

	"hello " ~ "world" ~ \n	// forms the string 'h','e','l','l','o',' ','w','o','r','l','d',linefeed
	
The following are all equivalent:
	"ab" "c"
	'ab' 'c'
	'a' "bc"
	"a" ~ "b" ~ "c"
	\0x61"bc"
	

Integer Literals

	IntegerLiteral:
		Integer
		Integer IntegerSuffix

	Integer:
		Decimal
		Binary
		Octal
		Hexadecimal

	IntegerSuffix:
		l
		L
		u
		U
		lu
		Lu
		lU
		LU
		ul
		uL
		Ul
		UL

	Decimal:
		0
		NonZeroDigit
		NonZeroDigit Decimal

	Binary:
		0b BinaryDigits
		0B BinaryDigits

	Octal:
		0 OctalDigits

	Hexadecimal:
		0x HexDigits
		0X HexDigits
	
Integers can be specified in decimal, binary, octal, or hexadecimal.

Decimal integers are a sequence of decimal digits.

Binary integers are a sequence of binary digits preceded by a '0b'.

Octal integers are a sequence of octal digits preceded by a '0'.

Hexadecimal integers are a sequence of hexadecimal digits preceded by a '0x' or followed by an 'h'.

Integers can be immediately followed by one 'l' or one 'u' or both.

The type of the integer is resolved as follows:

  1. If it is decimal it is the last representable of ulong, long, or int.
  2. If it is not decimal, it is the last representable of ulong, long, uint, or int.
  3. If it has the 'u' suffix, it is the last representable of ulong or uint.
  4. If it has the 'l' suffix, it is the last representable of ulong or long.
  5. If it has the 'u' and 'l' suffixes, it is ulong.

Floating Literals

	FloatLiteral:
		Float
		Float FloatSuffix
		Float ImaginarySuffix
		Float FloatSuffix ImaginarySuffix

	Float:
		DecimalFloat
		HexFloat

	FloatSuffix:
		f
		F
		l
		L

	ImaginarySuffix:
		i
		I
	
Floats can be in decimal or hexadecimal format, as in standard C.

Hexadecimal floats are preceded with a 0x and the exponent is a p or P followed by a power of 2.

Floats can be followed by one f, F, l or L suffix. The f or F suffix means it is a float, and l or L means it is an extended.

If a floating literal is followed by i or I, then it is an ireal (imaginary) type.

Examples:

	0x1.FFFFFFFFFFFFFp1023		// double.max
	0x1p-52				// double.epsilon
	1.175494351e-38F		// float.min
	6.3i				// idouble 6.3
	6.3fi				// ifloat 6.3
	6.3LI				// ireal 6.3
	
It is an error if the literal exceeds the range of the type. It is not an error if the literal is rounded to fit into the significant digits of the type.

Complex literals are not tokens, but are assembled from real and imaginary expressions in the semantic analysis:

	4.5 + 6.2i		// complex number
	

Keywords

Keywords are reserved identifiers.
	Keyword:
		abstract
		alias
		align
		asm
		assert
		auto

		bit
		body
		break
		byte

		case
		cast
		catch
		cent
		char
		class
		cfloat
		cdouble
		creal
		const
		continue

		debug
		default
		delegate
		delete
		deprecated
		do
		double

		else
		enum
		export
		extern

		false
		final
		finally
		float
		for
		function

		super
		null
		new
		short
		int
		long
		ifloat
		idouble
		ireal
		if
		switch
		synchronized
		return
		goto
		struct
		interface
		import
		static
		override
		in
		out
		inout
		private
		protected
		public
		invariant
		real

		this
		throw
		true
		try
		typedef

		ubyte
		ucent
		uint
		ulong
		union
		ushort

		version
		void
		volatile

		wchar
		while
		with
	

Tokens

	Token:
		Identifier
		StringLiteral
		IntegerLiteral
		FloatLiteral
		Keyword
		/
		/=
		.
		..
		...
		&
		&=
		&&
		|
		|=
		||
		-
		-=
		--
		+
		+=
		++
		<
		<=
		<<
		<<=
		<>
		<>=
		>
		>=
		>>=
		>>>=
		>>
		>>>
		!
		!=
		!==
		!<>
		!<>=
		!<
		!<=
		!>
		!>=
		(
		)
		[
		]
		{
		}
		?
		,
		;
		:
		$
		=
		==
		===
		*
		*=
		%
		%=
		^
		^=
		~
		~=
	

Pragmas

Pragmas are special token sequences that give instructions to the compiler. Pragmas are processed by the lexical analyzer, may appear between any other tokens, and do not affect the syntax parsing.

There is currently only one pragma, the #line pragma.

	Pragma
		# line Integer EndOfLine
		# line Integer Filespec EndOfLine

	Filespec
		" Characters "
	
This sets the source line number to Integer, and optionally the source file name to Filespec, beginning with the next line of source text. The source file and line number is used for printing error messages and for mapping generated code back to the source for the symbolic debugging output.

For example:

	int #line 6 "foo\bar"
	x;			// this is now line 6 of file foo\bar
	
Note that the backslash character is not treated specially inside Filespec strings.
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