Skip to content

G
go
Commit ff70f09d authored by Rob Pike's avatar Rob Pike
Browse files
Options

Rewrite lexical section. 

Put grammar productions into a box with a separate background color.

R=gri
DELTA=397  (132 added, 49 deleted, 216 changed)
OCL=25235
CL=25258
parent fd1f3830
Hide whitespace changes
Inline Side-by-side
Showing with 320 additions and 243 deletions
doc/go_spec.html
View file @ ff70f09d
......@@ -156,13 +156,13 @@ compile/link model to generate executable binaries.
The grammar is compact and regular, allowing for easy analysis by
automatic tools such as integrated development environments.
</p>
<hr>
<hr/>
<h2>Notation</h2>
<p>
The syntax is specified using Extended Backus-Naur Form (EBNF):
</p>
<pre>
<pre class="grammar">
Production = production_name "=" Expression .
Expression = Alternative { "|" Alternative } .
Alternative = Term { Term } .
......@@ -176,7 +176,7 @@ Repetition = "{" Expression "}" .
Productions are expressions constructed from terms and the following
operators, in increasing precedence:
</p>
<pre>
<pre class="grammar">
| alternation
() grouping
[] option (0 or 1 times)
......@@ -199,23 +199,21 @@ The form <tt>"a ... b"</tt> represents the set of characters from
Where possible, recursive productions are used to express evaluation order
and operator precedence syntactically.
</p>
<hr>
<hr/>
<h2>Source code representation</h2>
Source code is Unicode text encoded in UTF-8.
<p>
Tokenization follows the usual rules. Source text is case-sensitive.
<p>
White space is blanks, newlines, carriage returns, or tabs.
<p>
Comments are // to end of line or /* */ without nesting and are treated as white space.
Source code is Unicode text encoded in UTF-8. The text is not
canonicalized, so a single accented code point is distinct from the
same character constructed from combining an accent and a letter;
those are treated as two code points. For simplicity, this document
will use the term <i>character</i> to refer to a Unicode code point.
</p>
<p>
Some Unicode characters (e.g., the character U+00E4) may be representable in
two forms, as a single code point or as two code points. For simplicity of
implementation, Go treats these as distinct characters: each Unicode code
point is a single character in Go.
Each code point is distinct; for instance, upper and lower case letters
are different characters.
</p>
<h3>Characters</h3>
......@@ -223,37 +221,66 @@ point is a single character in Go.
The following terms are used to denote specific Unicode character classes:
</p>
<ul>
<li>unicode_char an arbitrary Unicode code point
<li>unicode_letter a Unicode code point classified as "Letter"
<li>capital_letter a Unicode code point classified as "Letter, uppercase"
<li>unicode_char an arbitrary Unicode code point</li>
<li>unicode_letter a Unicode code point classified as "Letter"</li>
<li>capital_letter a Unicode code point classified as "Letter, uppercase"</li>
<li>unicode_digit a Unicode code point classified as "Digit"</li>
</ul>
(The Unicode Standard, Section 4.5 General Category - Normative.)
<h3>Letters and digits</h3>
<pre>
<p>
The underscore character <tt>_</tt> (U+005F) is considered a letter.
</>
<pre class="grammar">
letter = unicode_letter | "_" .
decimal_digit = "0" ... "9" .
octal_digit = "0" ... "7" .
hex_digit = "0" ... "9" | "A" ... "F" | "a" ... "f" .
</pre>
<hr>
<hr/>
<h2>Lexical elements</h2>
<h2>Vocabulary</h2>
<h3>Comments</h3>
Tokens make up the vocabulary of the Go language. They consist of
identifiers, numbers, strings, operators, and delimitors.
<p>
There are two forms of comments. The first starts at the character
sequence <tt>//</tt> and continues through the next newline. The
second starts at the character sequence <tt>/*</tt> and continues
through the character sequence <tt>*/</tt>. Comments do not nest.
</p>
<h3>Tokens</h3>
<p>
Tokens form the vocabulary of the Go language.
There are four classes: identifiers, keywords, operators
and delimiters, and literals. <i>White space</i>, formed from
blanks, tabs, and newlines, is ignored except as it separates tokens
that would otherwise combine into a single token. Comments
behave as white space. While breaking the input into tokens,
the next token is the longest sequence of characters that form a
valid token.
</p>
<h3>Identifiers</h3>
An identifier is a name for a program entity such as a variable, a
type, a function, etc.
<pre>
identifier = letter { letter | decimal_digit } .
<p>
Identifiers name program entities such as variables and types.
An identifier is a sequence of one or more letters and digits.
The first character in an identifier must be a letter.
</p>
<pre class="grammar">
identifier = letter { letter | unicode_digit } .
</pre>
Exported identifiers (§Exported identifiers) start with a capital_letter.
<p>
Exported identifiers (§Exported identifiers) start with a <tt>capital_letter</tt>.
<br>
<font color=red>TODO: This sentence feels out of place.</font>
</p>
<pre>
a
_x9
......@@ -262,16 +289,46 @@ ThisVariableIsExported
</pre>
Some identifiers are predeclared (§Predeclared identifiers).
<h3>Keywords</h3>
<h3>Numeric literals</h3>
<p>
The following keywords are reserved and may not be used as identifiers.
</p>
<pre class="grammar">
break default func interface select
case defer go map struct
chan else goto package switch
const fallthrough if range type
continue for import return var
</pre>
An integer literal represents a mathematically ideal integer constant
of arbitrary precision, or 'ideal int'.
<pre>
int_lit = decimal_int | octal_int | hex_int .
decimal_int = ( "1" ... "9" ) { decimal_digit } .
octal_int = "0" { octal_digit } .
hex_int = "0" ( "x" | "X" ) hex_digit { hex_digit } .
<h3>Operators and Delimiters</h3>
<p>
The following character sequences represent operators, delimiters, and other special tokens:
</p>
<pre class="grammar">
+ &amp; += &amp;= &amp;&amp; == != ( )
- | -= |= || &lt; &lt;= [ ]
* ^ *= ^= &lt;- &gt; &gt;= { }
/ << /= <<= ++ = := , ;
% >> %= >>= -- ! ... . :
</pre>
<h3>Integer literals</h3>
<p>
An integer literal is a sequence of one or more digits in the
corresponding base, which may be 8, 10, or 16. An optional prefix
sets a non-decimal base: <tt>0</tt> for octal, <tt>0x</tt> or
<tt>0X</tt> for hexadecimal. In hexadecimal literals, letters
<tt>a-f</tt> and <tt>A-F</tt> represent values 10 through 15.
</p>
<pre class="grammar">
int_lit = decimal_lit | octal_lit | hex_lit .
decimal_lit = ( "1" ... "9" ) { decimal_digit } .
octal_lit = "0" { octal_digit } .
hex_lit = "0" ( "x" | "X" ) hex_digit { hex_digit } .
</pre>
<pre>
......@@ -281,14 +338,20 @@ hex_int = "0" ( "x" | "X" ) hex_digit { hex_digit } .
170141183460469231731687303715884105727
</pre>
A floating point literal represents a mathematically ideal floating point
constant of arbitrary precision, or 'ideal float'.
<pre>
float_lit =
decimals "." [ decimals ] [ exponent ] |
decimals exponent |
"." decimals [ exponent ] .
<h3>Floating-point literals</h3>
<p>
A floating-point literal is a decimal representation of a floating-point
number. It has an integer part, a decimal point, a fractional part,
and an exponent part. The integer and fractional part comprise
decimal digits; the exponent part is an <tt>e</TT> or <tt>E</tt>
followed by an optionally signed decimal exponent. One of the
integer part or the fractional part may be elided; one of the decimal
point or the exponent may be elided.
</p>
<pre class="grammar">
float_lit = decimals "." [ decimals ] [ exponent ] |
decimals exponent |
"." decimals [ exponent ] .
decimals = decimal_digit { decimal_digit } .
exponent = ( "e" | "E" ) [ "+" | "-" ] decimals .
</pre>
......@@ -303,79 +366,90 @@ exponent = ( "e" | "E" ) [ "+" | "-" ] decimals .
.12345E+5
</pre>
Numeric literals are unsigned. A negative constant is formed by
applying the unary prefix operator "-" (§Arithmetic operators).
<p>
An 'ideal number' is either an 'ideal int' or an 'ideal float'.
<h3>Ideal numbers</h3>
<p>
Only when an ideal number (or an arithmetic expression formed
solely from ideal numbers) is bound to a variable or used in an expression
or constant of fixed-size integers or floats it is required to fit
a particular size. In other words, ideal numbers and arithmetic
upon them are not subject to overflow; only use of them in assignments
or expressions involving fixed-size numbers may cause overflow, and thus
an error (§Expressions).
Integer literals represent values of arbitrary precision, or <i>ideal
integers</i>. Similarly, floating-point literals represent values
of arbitrary precision, or <i>ideal floats</i>. These <i>ideal
numbers</i> have no size or type and cannot overflow. However,
when (used in an expression) assigned to a variable or typed constant,
the destination must be able to represent the assigned value.
</p>
<p>
Implementation restriction: A compiler may implement ideal numbers
by choosing a "sufficiently large" internal representation of such
numbers.
by choosing a large internal representation of such numbers.
<br>
<font color=red>TODO: This is too vague. It used to say "sufficiently"
but that doesn't help. Define a minimum?</font>
</p>
<h3>Character and string literals</h3>
<h3>Character literals</h3>
<p>
Character and string literals are almost the same as in C, with the
following differences:
A character literal represents an integer value, typically a
Unicode code point, as one or more characters enclosed in single
quotes. Within the quotes, any character may appear except single
quote and newline. A single quoted character represents itself,
while multi-character sequences beginning with a backslash encode
values in various formats.
</p>
<ul>
<li>The encoding is UTF-8
<li>`` strings exist; they do not interpret backslashes
<li>Octal character escapes are always 3 digits ("\077" not "\77")
<li>Hexadecimal character escapes are always 2 digits ("\x07" not "\x7")
</ul>
The rules are:
<pre>
escaped_char = "\" ( "a" | "b" | "f" | "n" | "r" | "t" | "v" | "\" | "'" | """ ) .
</pre>
<p>
A unicode_value takes one of four forms:
The simplest form represents the single character within the quotes;
since Go source text is Unicode characters encoded in UTF-8, multiple
UTF-8-encoded bytes may represent a single integer value. For
instance, the literal <tt>'a'</tt> holds a single byte representing
a literal <tt>a</tt>, Unicode U+0061, value <tt>0x61</tt>, while
<tt>'ä'</tt> holds two bytes (<tt>0xc3</tt> <tt>0xa4</tt>) representing
a literal <tt>a</tt>-dieresis, U+00E4, value <tt>0xe4</tt>.
</p>
<ul>
<li>The UTF-8 encoding of a Unicode code point. Since Go source
text is in UTF-8, this is the obvious translation from input
text into Unicode characters.
<li>The usual list of C backslash escapes: "\n", "\t", etc.
Within a character or string literal, only the corresponding quote character
is a legal escape (this is not explicitly reflected in the above syntax).
<li>A `little u' value, such as "\u12AB". This represents the Unicode
code point with the corresponding hexadecimal value. It always
has exactly 4 hexadecimal digits.
<li>A `big U' value, such as "\U00101234". This represents the
Unicode code point with the corresponding hexadecimal value.
It always has exactly 8 hexadecimal digits.
</ul>
Some values that can be represented this way are illegal because they
are not valid Unicode code points. These include values above
0x10FFFF and surrogate halves.
<p>
An octal_byte_value contains three octal digits. A hex_byte_value
contains two hexadecimal digits. (Note: This differs from C but is
simpler.)
Several backslash escapes allow arbitrary values to be represented
as ASCII text. There are four ways to represent the integer value
as a numeric constant: <tt>\x</tt> followed by exactly two hexadecimal
digits; <tt>\u</tt> followed by exactly four hexadecimal digits;
<tt>\U</tt> followed by exactly eight hexadecimal digits, and a
plain backslash <tt>\</tt> followed by exactly three octal digits.
In each case the value of the literal is the value represented by
the digits in the corresponding base.
</p>
<p>
It is erroneous for an octal_byte_value to represent a value larger than 255.
(By construction, a hex_byte_value cannot.)
Although these representations all result in an integer, they have
different valid ranges. Octal escapes must represent a value between
0 and 255 inclusive. (Hexadecimal escapes satisfy this condition
by construction). The `Unicode' escapes <tt>\u</tt> and <tt>\U</tt>
represent Unicode code points so within them some values are illegal,
in particular those above <tt>0x10FFFF</tt> and surrogate halves.
</p>
<p>
A character literal is a form of unsigned integer constant. Its value
is that of the Unicode code point represented by the text between the
quotes.
After a backslash, certain single-character escapes represent special values:
</p>
<pre class="grammar">
\a U+0007 alert or bell
\b U+0008 backspace
\f U+000C form feed
\n U+000A line feed or newline
\r U+000D carriage return
\t U+0009 horizontal tab
\v U+000b vertical tab
\\ U+005c backslash
\' U+0027 single quote (valid escape only within character literals)
\" U+0022 double quote (valid escape only within string literals)
</pre>
<p>
All other sequences are illegal inside character literals.
</p>
<pre class="grammar">
char_lit = "'" ( unicode_value | byte_value ) "'" .
unicode_value = unicode_char | little_u_value | big_u_value | escaped_char .
byte_value = octal_byte_value | hex_byte_value .
octal_byte_value = "\" octal_digit octal_digit octal_digit .
hex_byte_value = "\" "x" hex_digit hex_digit .
little_u_value = "\" "u" hex_digit hex_digit hex_digit hex_digit .
big_u_value = "\" "U" hex_digit hex_digit hex_digit hex_digit
hex_digit hex_digit hex_digit hex_digit .
escaped_char = "\" ( "a" | "b" | "f" | "n" | "r" | "t" | "v" | "\" | "'" | """ ) .
</pre>
<pre>
'a'
'ä'
......@@ -390,30 +464,47 @@ quotes.
'\U00101234'
</pre>
String literals come in two forms: double-quoted and back-quoted.
Double-quoted strings have the usual properties; back-quoted strings
do not interpret backslashes at all.
<p>
The value of a character literal is an ideal integer, just as with
integer literals.
</p>
<pre>
string_lit = raw_string_lit | interpreted_string_lit .
raw_string_lit = "`" { unicode_char } "`" .
<h3>String literals</h3>
<p>
String literals represent constant values of type <tt>string</tt>.
There are two forms: raw string literals and interpreted string
literals.
</p>
<p>
Raw string literals are character sequences between back quotes
<tt>``</tt>. Within the quotes, any character is legal except
newline and back quote. The value of a raw string literal is the
string composed of the uninterpreted bytes between the quotes;
in particular, backslashes have no special meaning.
</p>
<p>
Interpreted string literals are character sequences between double
quotes <tt>&quot;&quot;</tt>. The text between the quotes forms the
value of the literal, with backslash escapes interpreted as they
are in character literals (except that <tt>\'</tt> is illegal and
<tt>\"</tt> is legal). The three-digit octal (<tt>\000</tt>)
and two-digit hexadecimal (<tt>\x00</tt>) escapes represent individual
<i>bytes</i> of the resulting string; all other escapes represent
the (possibly multi-byte) UTF-8 encoding of individual <i>characters</i>.
Thus inside a string literal <tt>\377</tt> and <tt>\xFF</tt> represent
a single byte of value <tt>0xFF</tt>=255, while <tt>ÿ</tt>,
<tt>\u00FF</tt>, <tt>\U000000FF</tt> and <tt>\xc3\xbf</tt> represent
the two bytes <tt>0xc3 0xbf</tt> of the UTF-8 encoding of character
U+00FF.
</p>
<pre class="grammar">
string_lit = raw_string_lit | interpreted_string_lit .
raw_string_lit = "`" { unicode_char } "`" .
interpreted_string_lit = """ { unicode_value | byte_value } """ .
</pre>
A string literal has type "string" (§Strings). Its value is constructed
by taking the byte values formed by the successive elements of the
literal. For byte_values, these are the literal bytes; for
unicode_values, these are the bytes of the UTF-8 encoding of the
corresponding Unicode code points. Note that
"\u00FF"
and
"\xFF"
are
different strings: the first contains the two-byte UTF-8 expansion of
the value 255, while the second contains a single byte of value 255.
The same rules apply to raw string literals, except the contents are
uninterpreted UTF-8.
<pre>
`abc`
`\n`
......@@ -426,61 +517,38 @@ uninterpreted UTF-8.
"\xff\u00FF"
</pre>
<p>
These examples all represent the same string:
</p>
<pre>
"日本語" // UTF-8 input text
`日本語` // UTF-8 input text as a raw literal
"\u65e5\u672c\u8a9e" // The explicit Unicode code points
"\U000065e5\U0000672c\U00008a9e" // The explicit Unicode code points
"日本語" // UTF-8 input text
`日本語` // UTF-8 input text as a raw literal
"\u65e5\u672c\u8a9e" // The explicit Unicode code points
"\U000065e5\U0000672c\U00008a9e" // The explicit Unicode code points
"\xe6\x97\xa5\xe6\x9c\xac\xe8\xaa\x9e" // The explicit UTF-8 bytes
</pre>
Adjacent strings separated only by whitespace (including comments)
are concatenated into a single string. The following two lines
represent the same string:
<p>
Adjacent string literals separated only by the empty string, white
space, or comments are concatenated into a single string literal.
</p>
<pre class="grammar">
StringLit = string_lit { string_lit } .
</pre>
<pre>
"Alea iacta est."
"Alea " /* The die */ `iacta est` /* is cast */ "."
</pre>
The language does not canonicalize Unicode text or evaluate combining
forms. The text of source code is passed uninterpreted.
<p>
If the source code represents a character as two code points, such as
a combining form involving an accent and a letter, the result will be
an error if placed in a character literal (it is not a single code
point), and will appear as two code points if placed in a string
literal.
<h3>Operators and delimitors</h3>
The following special character sequences serve as operators or delimitors:
<pre>
+ &amp; += &amp;= &amp;&amp; == != ( )
- | -= |= || < <= [ ]
* ^ *= ^= <- > >= { }
/ << /= <<= ++ = := , ;
% >> %= >>= -- ! ... . :
</pre>
<h3>Reserved words</h3>
The following words are reserved and must not be used as identifiers:
<pre>
break default func interface select
case defer go map struct
chan else goto package switch
const fallthrough if range type
continue for import return var
</pre>
<hr>
</p>
<hr/>
<h2>Declarations and scope rules</h2>
......@@ -488,7 +556,7 @@ A declaration ``binds'' an identifier to a language entity (such as
a package, constant, type, struct field, variable, parameter, result,
function, method) and specifies properties of that entity such as its type.
<pre>
<pre class="grammar">
Declaration = ConstDecl | TypeDecl | VarDecl | FunctionDecl | MethodDecl .
</pre>
......@@ -535,30 +603,33 @@ same identifier declared in an outer block.
<h3>Predeclared identifiers</h3>
<p>
The following identifiers are predeclared:
</p>
<p>
All basic types:
<pre>
</p>
<pre class="grammar">
bool, byte, uint8, uint16, uint32, uint64, int8, int16, int32, int64,
float32, float64, string
</pre>
A set of platform-specific convenience types:
<pre>
<pre class="grammar">
uint, int, float, uintptr
</pre>
The predeclared constants:
<pre>
<pre class="grammar">
true, false, iota, nil
</pre>
The predeclared functions (note: this list is likely to change):
<pre>
<pre class="grammar">
cap(), convert(), len(), make(), new(), panic(), panicln(), print(), println(), typeof(), ...
</pre>
......@@ -584,7 +655,7 @@ are never exported, but non-global fields/methods may be exported.
A constant declaration binds an identifier to the value of a constant
expression (§Constant expressions).
<pre>
<pre class="grammar">
ConstDecl = "const" ( ConstSpec | "(" [ ConstSpecList ] ")" ) .
ConstSpecList = ConstSpec { ";" ConstSpec } [ ";" ] .
ConstSpec = IdentifierList [ CompleteType ] [ "=" ExpressionList ] .
......@@ -753,7 +824,7 @@ const (
A type declaration specifies a new type and binds an identifier to it.
The identifier is called the ``type name''; it denotes the type.
<pre>
<pre class="grammar">
TypeDecl = "type" ( TypeSpec | "(" [ TypeSpecList ] ")" ) .
TypeSpecList = TypeSpec { ";" TypeSpec } [ ";" ] .
TypeSpec = identifier Type .
......@@ -791,7 +862,7 @@ The variable type must be a complete type (§Types).
In some forms of declaration the type of the initial value defines the type
of the variable.
<pre>
<pre class="grammar">
VarDecl = "var" ( VarSpec | "(" [ VarSpecList ] ")" ) .
VarSpecList = VarSpec { ";" VarSpec } [ ";" ] .
VarSpec = IdentifierList ( CompleteType [ "=" ExpressionList ] | "=" ExpressionList ) .
......@@ -827,13 +898,13 @@ var f = 3.1415 // f has float type
The syntax
<pre>
<pre class="grammar">
SimpleVarDecl = IdentifierList ":=" ExpressionList .
</pre>
is shorthand for
<pre>
<pre class="grammar">
"var" IdentifierList = ExpressionList .
</pre>
......@@ -846,7 +917,7 @@ ch := new(chan int);
Also, in some contexts such as "if", "for", or "switch" statements,
this construct can be used to declare local temporary variables.
<hr>
<hr/>
<h2>Types</h2>
......@@ -857,8 +928,8 @@ A type may be specified by a type name (§Type declarations) or a type literal.
A type literal is a syntactic construct that explicitly specifies the
composition of a new type in terms of other (already declared) types.
<pre>
Type = TypeName | TypeLit .
<pre class="grammar">
Type = TypeName | TypeLit | "(" Type ")" .
TypeName = QualifiedIdent.
TypeLit =
ArrayType | StructType | PointerType | FunctionType | InterfaceType |
......@@ -881,7 +952,7 @@ type of a pointer type, may be incomplete). Incomplete types are subject to usag
restrictions; for instance the type of a variable must be complete where the
variable is declared.
<pre>
<pre class="grammar">
CompleteType = Type .
</pre>
......@@ -912,7 +983,7 @@ and strings.
The following list enumerates all platform-independent numeric types:
<pre>
<pre class="grammar">
byte same as uint8 (for convenience)
uint8 the set of all unsigned 8-bit integers (0 to 255)
......@@ -944,7 +1015,7 @@ its corresponding unsigned type without loss).
Additionally, Go declares a set of platform-specific numeric types for
convenience:
<pre>
<pre class="grammar">
uint at least 32 bits, at most the size of the largest uint type
int at least 32 bits, at most the size of the largest int type
float at least 32 bits, at most the size of the largest float type
......@@ -1006,7 +1077,7 @@ same type, called the element type. The element type must be a complete type
negative. The elements of an array are designated by indices
which are integers from 0 through the length - 1.
<pre>
<pre class="grammar">
ArrayType = "[" ArrayLength "]" ElementType .
ArrayLength = Expression .
ElementType = CompleteType .
......@@ -1046,7 +1117,7 @@ an identifier and type for each field. Within a struct type no field
identifier may be declared twice and all field types must be complete
types (§Types).
<pre>
<pre class="grammar">
StructType = "struct" [ "{" [ FieldDeclList ] "}" ] .
FieldDeclList = FieldDecl { ";" FieldDecl } [ ";" ] .
FieldDecl = (IdentifierList CompleteType | [ "*" ] TypeName) [ Tag ] .
......@@ -1134,7 +1205,7 @@ equal type only.
A pointer type denotes the set of all pointers to variables of a given
type, called the ``base type'' of the pointer, and the value "nil".
<pre>
<pre class="grammar">
PointerType = "*" BaseType .
BaseType = Type .
</pre>
......@@ -1178,7 +1249,7 @@ Pointer arithmetic of any kind is not permitted.
A function type denotes the set of all functions with the same parameter
and result types, and the value "nil".
<pre>
<pre class="grammar">
FunctionType = "func" Signature .
Signature = "(" [ ParameterList ] ")" [ Result ] .
ParameterList = ParameterDecl { "," ParameterDecl } .
......@@ -1236,7 +1307,7 @@ Type interfaces may be specified explicitly by interface types.
An interface type denotes the set of all types that implement at least
the set of methods specified by the interface type, and the value "nil".
<pre>
<pre class="grammar">
InterfaceType = "interface" [ "{" [ MethodSpecList ] "}" ] .
MethodSpecList = MethodSpec { ";" MethodSpec } [ ";" ] .
MethodSpec = IdentifierList Signature | TypeName .
......@@ -1344,7 +1415,7 @@ The number of elements of a slice is called its length; it is never negative.
The elements of a slice are designated by indices which are
integers from 0 through the length - 1.
<pre>
<pre class="grammar">
SliceType = "[" "]" ElementType .
</pre>
......@@ -1436,7 +1507,7 @@ each be of a specific complete type (§Types) called the key and value type,
respectively. The number of entries in a map is called its length; it is never
negative.
<pre>
<pre class="grammar">
MapType = "map" "[" KeyType "]" ValueType .
KeyType = CompleteType .
ValueType = CompleteType .
......@@ -1491,7 +1562,7 @@ A channel provides a mechanism for two concurrently executing functions
to synchronize execution and exchange values of a specified type. This
type must be a complete type (§Types). <font color=red>(TODO could it be incomplete?)</font>
<pre>
<pre class="grammar">
ChannelType = Channel | SendChannel | RecvChannel .
Channel = "chan" ValueType .
SendChannel = "chan" "&lt;-" ValueType .
......@@ -1544,7 +1615,7 @@ the same ValueType. They are equal if both values were created by the same
Types may be ``different'', ``structurally equal'', or ``identical''.
Go is a type-safe language; generally different types cannot be mixed
in binary operations, and values cannot be assigned to variables of different
types. However, values may be assigned to variables of structually
types. However, values may be assigned to variables of structurally
equal types. Finally, type guards succeed only if the dynamic type
is identical to or implements the type tested against (§Type guards).
<p>
......@@ -1659,7 +1730,7 @@ struct { a, b *T5 } and struct { a, b *T5 }
As an example, "T0" and "T1" are equal but not identical because they have
different declarations.
<hr>
<hr/>
<h2>Expressions</h2>
......@@ -1688,7 +1759,7 @@ should be ideal number, because for arrays, it is a constant.
Operands denote the elementary values in an expression.
<pre>
<pre class="grammar">
Operand = Literal | QualifiedIdent | "(" Expression ")" .
Literal = BasicLit | CompositeLit | FunctionLit .
BasicLit = int_lit | float_lit | char_lit | StringLit .
......@@ -1713,7 +1784,7 @@ A qualified identifier is an identifier qualified by a package name.
TODO(gri) expand this section.
</font>
<pre>
<pre class="grammar">
QualifiedIdent = { PackageName "." } identifier .
PackageName = identifier .
</pre>
......@@ -1725,7 +1796,7 @@ Literals for composite data structures consist of the type of the value
followed by a braced expression list for array, slice, and structure literals,
or a list of expression pairs for map literals.
<pre>
<pre class="grammar">
CompositeLit = LiteralType "(" [ ( ExpressionList | ExprPairList ) [ "," ] ] ")" .
LiteralType = Type | "[" "..." "]" ElementType .
ExprPairList = ExprPair { "," ExprPair } .
......@@ -1798,7 +1869,7 @@ A function literal represents an anonymous function. It consists of a
specification of the function type and the function body. The parameter
and result types of the function type must all be complete types (§Types).
<pre>
<pre class="grammar">
FunctionLit = "func" Signature Block .
Block = "{" [ StatementList ] "}" .
</pre>
......@@ -1825,7 +1896,7 @@ as they are accessible in any way.
<h3>Primary expressions</h3>
<pre>
<pre class="grammar">
PrimaryExpr =
Operand |
PrimaryExpr Selector |
......@@ -2175,7 +2246,7 @@ in f_extra.
Operators combine operands into expressions.
<pre>
<pre class="grammar">
Expression = UnaryExpr | Expression binaryOp UnaryExpr .
UnaryExpr = PrimaryExpr | unary_op UnaryExpr .
......@@ -2210,7 +2281,7 @@ The operand types in binary operations must be equal, with the following excepti
Unary operators have the highest precedence. They are evaluated from
right to left. Note that "++" and "--" are outside the unary operator
hierachy (they are statements) and they apply to the operand on the left.
hierarchy (they are statements) and they apply to the operand on the left.
Specifically, "*p++" means "(*p)++" in Go (as opposed to "*(p++)" in C).
<p>
There are six precedence levels for binary operators:
......@@ -2219,7 +2290,7 @@ operators, comparison operators, communication operators,
"&amp;&amp;" (logical and), and finally "||" (logical or) with the
lowest precedence:
<pre>
<pre class="grammar">
Precedence Operator
6 * / % &lt;&lt; >> &amp;
5 + - | ^
......@@ -2251,7 +2322,7 @@ type as the first operand. The four standard arithmetic operators ("+", "-",
"*", "/") apply to both integer and floating point types, while "+" also applies
to strings and arrays; all other arithmetic operators apply to integer types only.
<pre>
<pre class="grammar">
+ sum integers, floats, strings, arrays
- difference integers, floats
* product integers, floats
......@@ -2317,7 +2388,7 @@ Specifically, "x << 1" is the same as "x*2"; and "x >> 1" is the same as
For integer operands, the unary operators "+", "-", and "^" are defined as
follows:
<pre>
<pre class="grammar">
+x is 0 + x
-x negation is 0 - x
^x bitwise complement is m ^ x with m = "all bits set to 1"
......@@ -2347,7 +2418,7 @@ boolean values, pointer, interface, and channel types. Slice and
map types only support testing for equality against the predeclared value
"nil".
<pre>
<pre class="grammar">
== equal
!= not equal
< less
......@@ -2372,7 +2443,7 @@ and §Channel types, respectively.
Logical operators apply to boolean operands and yield a boolean result.
The right operand is evaluated conditionally.
<pre>
<pre class="grammar">
&amp;&amp; conditional and p &amp;&amp; q is "if p then q else false"
|| conditional or p || q is "if p then true else q"
! not !p is "not p"
......@@ -2580,13 +2651,13 @@ TODO: Complete this list as needed.
<p>
Constant expressions can be evaluated at compile time.
<hr>
<hr/>
<h2>Statements</h2>
Statements control execution.
<pre>
<pre class="grammar">
Statement =
Declaration | LabelDecl | EmptyStat |
SimpleStat | GoStat | ReturnStat | BreakStat | ContinueStat | GotoStat |
......@@ -2601,7 +2672,7 @@ SimpleStat =
Statements in a statement list are separated by semicolons, which can be
omitted in some cases as expressed by the OptSemicolon production.
<pre>
<pre class="grammar">
StatementList = Statement { OptSemicolon Statement } .
</pre>
......@@ -2623,14 +2694,14 @@ is an empty statement, a statement list can always be ``terminated'' with a semi
The empty statement does nothing.
<pre>
<pre class="grammar">
EmptyStat = .
</pre>
<h3>Expression statements</h3>
<pre>
<pre class="grammar">
ExpressionStat = Expression .
</pre>
......@@ -2648,14 +2719,14 @@ TODO: specify restrictions. 6g only appears to allow calls here.
The "++" and "--" statements increment or decrement their operands
by the (ideal) constant value 1.
<pre>
<pre class="grammar">
IncDecStat = Expression ( "++" | "--" ) .
</pre>
The following assignment statements (§Assignments) are semantically
equivalent:
<pre>
<pre class="grammar">
IncDec statement Assignment
x++ x += 1
x-- x -= 1
......@@ -2669,11 +2740,9 @@ For instance, "x++" cannot be used as an operand in an expression.
<h3>Assignments</h3>
<pre>
<pre class="grammar">
Assignment = ExpressionList assign_op ExpressionList .
</pre>
<pre>
assign_op = [ add_op | mul_op ] "=" .
</pre>
......@@ -2742,7 +2811,7 @@ and the "else" branch. If Expression evaluates to true,
the "if" branch is executed. Otherwise the "else" branch is executed if present.
If Condition is omitted, it is equivalent to true.
<pre>
<pre class="grammar">
IfStat = "if" [ [ SimpleStat ] ";" ] [ Expression ] Block [ "else" Statement ] .
</pre>
......@@ -2792,7 +2861,7 @@ without the surrounding Block:
Switches provide multi-way execution.
<pre>
<pre class="grammar">
SwitchStat = "switch" [ [ SimpleStat ] ";" ] [ Expression ] "{" { CaseClause } "}" .
CaseClause = SwitchCase ":" [ StatementList ] .
SwitchCase = "case" ExpressionList | "default" .
......@@ -2858,7 +2927,7 @@ case x == 4: f3();
A for statement specifies repeated execution of a block. The iteration is
controlled by a condition, a for clause, or a range clause.
<pre>
<pre class="grammar">
ForStat = "for" [ Condition | ForClause | RangeClause ] Block .
Condition = Expression .
</pre>
......@@ -2879,7 +2948,7 @@ additionally it may specify an init and post statement, such as an assignment,
an increment or decrement statement. The init statement may also be a (simple)
variable declaration; no variables can be declared in the post statement.
<pre>
<pre class="grammar">
ForClause = [ InitStat ] ";" [ Condition ] ";" [ PostStat ] .
InitStat = SimpleStat .
PostStat = SimpleStat .
......@@ -2917,7 +2986,7 @@ of iteration variables - and then executes the block. Iteration terminates
when all entries have been processed, or if the for statement is terminated
early, for instance by a break or return statement.
<pre>
<pre class="grammar">
RangeClause = IdentifierList ( "=" | ":=" ) "range" Expression .
</pre>
......@@ -2970,7 +3039,7 @@ A go statement starts the execution of a function as an independent
concurrent thread of control within the same address space. The expression
must be a function or method call.
<pre>
<pre class="grammar">
GoStat = "go" Expression .
</pre>
......@@ -2989,7 +3058,7 @@ A select statement chooses which of a set of possible communications
will proceed. It looks similar to a switch statement but with the
cases all referring to communication operations.
<pre>
<pre class="grammar">
SelectStat = "select" "{" { CommClause } "}" .
CommClause = CommCase ":" [ StatementList ] .
CommCase = "case" ( SendExpr | RecvExpr) | "default" .
......@@ -3067,7 +3136,7 @@ TODO: Make semantics more precise.
A return statement terminates execution of the containing function
and optionally provides a result value or values to the caller.
<pre>
<pre class="grammar">
ReturnStat = "return" [ ExpressionList ] .
</pre>
......@@ -3111,7 +3180,7 @@ func complex_f2() (re float, im float) {
Within a for, switch, or select statement, a break statement terminates
execution of the innermost such statement.
<pre>
<pre class="grammar">
BreakStat = "break" [ identifier ].
</pre>
......@@ -3133,7 +3202,7 @@ L: for i < n {
Within a for loop a continue statement begins the next iteration of the
loop at the post statement.
<pre>
<pre class="grammar">
ContinueStat = "continue" [ identifier ].
</pre>
......@@ -3144,7 +3213,7 @@ The optional identifier is analogous to that of a break statement.
A label declaration serves as the target of a goto, break or continue statement.
<pre>
<pre class="grammar">
LabelDecl = identifier ":" .
</pre>
......@@ -3159,7 +3228,7 @@ Error:
A goto statement transfers control to the corresponding label statement.
<pre>
<pre class="grammar">
GotoStat = "goto" identifier .
</pre>
......@@ -3187,7 +3256,7 @@ next case clause in a switch statement (§Switch statements). It may only
be used in a switch statement, and only as the last statement in a case
clause of the switch statement.
<pre>
<pre class="grammar">
FallthroughStat = "fallthrough" .
</pre>
......@@ -3197,7 +3266,7 @@ FallthroughStat = "fallthrough" .
A defer statement invokes a function whose execution is deferred to the moment
when the surrounding function returns.
<pre>
<pre class="grammar">
DeferStat = "defer" Expression .
</pre>
......@@ -3218,7 +3287,7 @@ for i := 0; i &lt;= 3; i++ {
}
</pre>
<hr>
<hr/>
<h2>Function declarations</h2>
......@@ -3227,7 +3296,7 @@ Functions contain declarations and statements. They may be
recursive. Except for forward declarations (see below), the parameter
and result types of the signature must all be complete types (§Type declarations).
<pre>
<pre class="grammar">
FunctionDecl = "func" identifier Signature [ Block ] .
</pre>
......@@ -3263,7 +3332,7 @@ it is declared within the scope of that type (§Type declarations). If the
receiver value is not needed inside the method, its identifier may be omitted
in the declaration.
<pre>
<pre class="grammar">
MethodDecl = "func" Receiver identifier Signature [ Block ] .
Receiver = "(" [ identifier ] [ "*" ] TypeName ")" .
</pre>
......@@ -3310,7 +3379,7 @@ base type and may be forward-declared.
<h3>Length and capacity</h3>
<pre>
<pre class="grammar">
Call Argument type Result
len(s) string, *string string length (in bytes)
......@@ -3345,7 +3414,7 @@ at any time the following relationship holds:
Conversions syntactically look like function calls of the form
<pre>
<pre class="grammar">
T(value)
</pre>
......@@ -3453,14 +3522,14 @@ TODO Once this has become clearer, connect new() and make() (new() may be
explained by make() and vice versa).
</font>
<hr>
<hr/>
<h2>Packages</h2>
A package is a package clause, optionally followed by import declarations,
followed by a series of declarations.
<pre>
<pre class="grammar">
Package = PackageClause { ImportDecl [ ";" ] } { Declaration [ ";" ] } .
</pre>
......@@ -3470,7 +3539,7 @@ purposes ($Declarations and scope rules).
Every source file identifies the package to which it belongs.
The file must begin with a package clause.
<pre>
<pre class="grammar">
PackageClause = "package" PackageName .
package Math
......@@ -3480,7 +3549,7 @@ package Math
A package can gain access to exported identifiers from another package
through an import declaration:
<pre>
<pre class="grammar">
ImportDecl = "import" ( ImportSpec | "(" [ ImportSpecList ] ")" ) .
ImportSpecList = ImportSpec { ";" ImportSpec } [ ";" ] .
ImportSpec = [ "." | PackageName ] PackageFileName .
......@@ -3568,7 +3637,7 @@ func main() {
}
</pre>
<hr>
<hr/>
<h2>Program initialization and execution</h2>
......@@ -3577,7 +3646,7 @@ or "new()", and no explicit initialization is provided, the memory is
given a default initialization. Each element of such a value is
set to the ``zero'' for that type: "false" for booleans, "0" for integers,
"0.0" for floats, '''' for strings, and "nil" for pointers and interfaces.
This intialization is done recursively, so for instance each element of an
This initialization is done recursively, so for instance each element of an
array of integers will be set to 0 if no other value is specified.
<p>
These two simple declarations are equivalent:
......@@ -3640,7 +3709,7 @@ invoking main.main().
<p>
When main.main() returns, the program exits.
<hr>
<hr/>
<h2>Systems considerations</h2>
......@@ -3652,7 +3721,7 @@ system. A package using "unsafe" must be vetted manually for type safety.
<p>
The package "unsafe" provides (at least) the following package interface:
<pre>
<pre class="grammar">
package unsafe
const Maxalign int
......@@ -3712,7 +3781,7 @@ The results of calls to "unsafe.Alignof", "unsafe.Offsetof", and
For the arithmetic types (§Arithmetic types), a Go compiler guarantees the
following sizes:
<pre>
<pre class="grammar">
type size in bytes
byte, uint8, int8 1
......@@ -3737,7 +3806,15 @@ A Go compiler guarantees the following minimal alignment properties:
unsafe.Alignof(x[0]), but at least 1.
</ol>
<hr>
<hr/>
<h2><font color=red>Differences between this doc and implementation - TODO</font></h2>
<p>
<font color=red>
Current implementation accepts only ASCII digits for digits; doc says Unicode.
<br>
</font>
</p>
</div>
</body>
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7