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Commit 1265a0c2 authored by Robert Griesemer's avatar Robert Griesemer
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- essentially reverted my change of yesterday with respect to char/string syntax 

- fixed indentation in many places
- fixed a couple of typos

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doc/go_lang.txt
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The Go Programming Language
----
(April 17, 2008)
(April 18, 2008)
This document is an informal specification/proposal for a new systems programming
language.
......@@ -194,12 +194,14 @@ Notation
The syntax is specified using Extended Backus-Naur Form (EBNF).
In particular:
- "" encloses lexical symbols (a backslash precedes a literal quote within a symbol)
- | separates alternatives
- | separates alternatives (least binding strength)
- () groups
- [] specifies an option (0 or 1 times)
- {} specifies repetition (0 to n times)
Lexical symbols are enclosed in double quotes '''' (the
double quote symbol is written as ''"'').
A production may be referenced from various places in this document
but is usually defined close to its first use. Productions and code
examples are indented.
......@@ -266,9 +268,9 @@ type, a function, etc. An identifier must not be a reserved word.
identifier = letter { letter | dec_digit } .
a
_x
ThisIsVariable9
a
_x
ThisIsVariable9
Types
......@@ -287,23 +289,23 @@ Go defines a number of basic types, referred to by their
predeclared type names. There are signed and unsigned integer
and floating point types:
bool the truth values true and false
bool the truth values true and false
uint8 the set of all unsigned 8-bit integers
uint16 the set of all unsigned 16-bit integers
uint32 the set of all unsigned 32-bit integers
unit64 the set of all unsigned 64-bit integers
uint8 the set of all unsigned 8-bit integers
uint16 the set of all unsigned 16-bit integers
uint32 the set of all unsigned 32-bit integers
unit64 the set of all unsigned 64-bit integers
byte alias for uint8
byte alias for uint8
int8 the set of all signed 8-bit integers, in 2's complement
int16 the set of all signed 16-bit integers, in 2's complement
int32 the set of all signed 32-bit integers, in 2's complement
int64 the set of all signed 64-bit integers, in 2's complement
int8 the set of all signed 8-bit integers, in 2's complement
int16 the set of all signed 16-bit integers, in 2's complement
int32 the set of all signed 32-bit integers, in 2's complement
int64 the set of all signed 64-bit integers, in 2's complement
float32 the set of all valid IEEE-754 32-bit floating point numbers
float64 the set of all valid IEEE-754 64-bit floating point numbers
float80 the set of all valid IEEE-754 80-bit floating point numbers
float32 the set of all valid IEEE-754 32-bit floating point numbers
float64 the set of all valid IEEE-754 64-bit floating point numbers
float80 the set of all valid IEEE-754 80-bit floating point numbers
Additionally, Go declares 4 basic types, uint, int, float, and double,
which are platform-specific. The bit width of these types corresponds to
......@@ -349,14 +351,14 @@ point value that is constrained only upon assignment.
int_lit = [ sign ] unsigned_int_lit .
unsigned_int_lit = decimal_int_lit | octal_int_lit | hex_int_lit .
decimal_int_lit = ( "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" )
{ dec_digit } .
{ dec_digit } .
octal_int_lit = "0" { oct_digit } .
hex_int_lit = "0" ( "x" | "X" ) hex_digit { hex_digit } .
float_lit = [ sign ] ( fractional_lit | exponential_lit ) .
fractional_lit = { dec_digit } ( dec_digit "." | "." dec_digit )
{ dec_digit } [ exponent ] .
exponential_lit = dec_digit { dec_digit } exponent .
exponent = ( "e" | "E" ) [ sign ] dec_digit { dec_digit }
exponent = ( "e" | "E" ) [ sign ] dec_digit { dec_digit } .
07
0xFF
......@@ -373,15 +375,15 @@ Strings behave like arrays of bytes, with the following properties:
contents of a string.
- No internal pointers: it is illegal to create a pointer to an inner
element of a string.
- They can be indexed: given string s1, s1[i] is a byte value.
- They can be concatenated: given strings s1 and s2, s1 + s2 is a value
combining the elements of s1 and s2 in sequence.
- Known length: the length of a string s1 can be obtained by the function/
operator len(s1). The length of a string is the number of bytes within.
- They can be indexed: given string "s1", "s1[i]" is a byte value.
- They can be concatenated: given strings "s1" and "s2", "s1 + s2" is a value
combining the elements of "s1" and "s2" in sequence.
- Known length: the length of a string "s1" can be obtained by the function/
operator "len(s1)". The length of a string is the number of bytes within.
Unlike in C, there is no terminal NUL byte.
- Creation 1: a string can be created from an integer value by a conversion;
the result is a string containing the UTF-8 encoding of that code point.
string('x') yields "x"; string(0x1234) yields the equivalent of "\u1234"
"string('x')" yields "x"; "string(0x1234)" yields the equivalent of "\u1234"
- Creation 2: a string can by created from an array of integer values (maybe
just array of bytes) by a conversion
a [3]byte; a[0] = 'a'; a[1] = 'b'; a[2] = 'c'; string(a) == "abc";
......@@ -390,38 +392,36 @@ Strings behave like arrays of bytes, with the following properties:
Character and string literals
----
Character and string literals are almost the same as in C, but with
UTF-8 required. This section is precise but can be skipped on first
reading.
Character and string literals are almost the same as in C, with the
following differences:
Character and string literals are similar to C except:
- Octal character escapes are always 3 digits (\077 not \77)
- Hexadecimal character escapes are always 2 digits (\x07 not \x7)
- Strings are UTF-8 and represent Unicode
- The encoding is UTF-8
- `` strings exist; they do not interpret backslashes
- Octal character escapes are always 3 digits ("\077" not "\77")
- Hexadecimal character escapes are always 2 digits ("\x07" not "\x7")
The rules are:
char_lit = "'" ( utf8_char_no_single_quote | "\" esc_seq ) "'" .
This section is precise but can be skipped on first reading. The rules are:
esc_seq =
"a" | "b" | "f" | "n" | "r" | "t" | "v" | "\" | "'" | "\"" |
oct_digit oct_digit oct_digit |
"x" hex_digit hex_digit |
"u" hex_digit hex_digit hex_digit hex_digit |
"U" hex_digit hex_digit hex_digit hex_digit
hex_digit hex_digit hex_digit hex_digit .
char_lit = "'" ( unicode_value | byte_value ) "'" .
unicode_value = utf8_char | little_u_value | big_u_value | escaped_char .
byte_value = octal_byte_value | hex_byte_value .
octal_byte_value = "\" oct_digit oct_digit oct_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" | "\" | "'" | """ ) .
A unicode_value takes one of four forms:
* 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.
* The usual list of C backslash escapes: \n \t etc.
* A `little u' value, such as \u12AB. This represents the Unicode
* The usual list of C backslash escapes: "\n", "\t", etc.
* 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.
* A `big U' value, such as \U00101234. This represents the
* 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.
......@@ -440,34 +440,34 @@ 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.
'a'
'ä'
'本'
'\t'
'\000'
'\007'
'\377'
'\x07'
'\xff'
'\u12e4'
'\U00101234'
'a'
'ä'
'本'
'\t'
'\000'
'\007'
'\377'
'\x07'
'\xff'
'\u12e4'
'\U00101234'
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.
string_lit = raw_string_lit | interpreted_string_lit .
raw_string_lit = "`" { utf8_char_no_back_quote } "`" .
interpreted_string_lit = "\"" { utf8_char_no_double_quote | "\\" esc_seq } "\"" .
raw_string_lit = "`" { utf8_char } "`" .
interpreted_string_lit = """ { unicode_value | byte_value } """ .
A string literal has type 'string'. 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"
"\u00FF"
and
"\xFF"
"\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.
......@@ -486,11 +486,11 @@ uninterpreted UTF-8.
These examples all represent the same string:
"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
"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
The language does not canonicalize Unicode text or evaluate combining
forms. The text of source code is passed uninterpreted.
......@@ -590,16 +590,16 @@ structure.
FieldDeclList = FieldDecl { ";" FieldDecl } .
FieldDecl = IdentifierList Type .
// An empty struct.
struct {}
// An empty struct.
struct {}
// A struct with 5 fields.
struct {
x, y int;
u float;
a []int;
f func();
}
// A struct with 5 fields.
struct {
x, y int;
u float;
a []int;
f func();
}
Compound Literals
----
......@@ -683,17 +683,17 @@ is called a 'send channel' or a 'receive channel'.
ChannelType = "chan" [ "<" | ">" ] ValueType .
chan any // a generic channel
chan int // a channel that can exchange only ints
chan> float // a channel that can only be used to send floats
chan< any // a channel that can receive (only) values of any type
chan any // a generic channel
chan int // a channel that can exchange only ints
chan> float // a channel that can only be used to send floats
chan< any // a channel that can receive (only) values of any type
Channel variables always have type pointer to channel.
It is an error to attempt to use a channel value and in
particular to dereference a channel pointer.
var ch *chan int;
ch = new(chan int); // new returns type *chan int
var ch *chan int;
ch = new(chan int); // new returns type *chan int
There are no channel literals.
......@@ -715,17 +715,17 @@ Functions can return multiple values simultaneously.
ParameterSection = [ IdentifierList ] Type .
Result = Type | "(" ParameterList ")" .
// Function types
func ()
func (a, b int, z float) bool
func (a, b int, z float) (success bool)
func (a, b int, z float) (success bool, result float)
// Function types
func ()
func (a, b int, z float) bool
func (a, b int, z float) (success bool)
func (a, b int, z float) (success bool, result float)
// Method types
func (p *T) . ()
func (p *T) . (a, b int, z float) bool
func (p *T) . (a, b int, z float) (success bool)
func (p *T) . (a, b int, z float) (success bool, result float)
// Method types
func (p *T) . ()
func (p *T) . (a, b int, z float) bool
func (p *T) . (a, b int, z float) (success bool)
func (p *T) . (a, b int, z float) (success bool, result float)
A variable can hold only a pointer to a function, not a function value.
In particular, v := func() {} creates a variable of type *func(). To call the
......@@ -750,11 +750,11 @@ or assigned to a variable of the corresponding function pointer type.
For now, a function literal can reference only its parameters, global
variables, and variables declared within the function literal.
// Function literal
func (a, b int, z float) bool { return a*b < int(z); }
// Function literal
func (a, b int, z float) bool { return a*b < int(z); }
// Method literal
func (p *T) . (a, b int, z float) bool { return a*b < int(z) + p.x; }
// Method literal
func (p *T) . (a, b int, z float) bool { return a*b < int(z) + p.x; }
Unresolved issues: Are there method literals? How do you use them?
......@@ -769,7 +769,7 @@ a method indicates the type of the struct by declaring a receiver of type
the declaration
func (p *Point) distance(float scale) float {
func (p *Point) distance(scale float) float {
return scale * (p.x*p.x + p.y*p.y);
}
......@@ -866,9 +866,9 @@ Attempts to convert/extract to an incompatible type will yield nil.
No other operations are defined (yet).
Note that type
interface {}
interface {}
is a special case that can match any struct type, while type
any
any
can match any type at all, including basic types, arrays, etc.
TODO: details about reflection
......@@ -1098,20 +1098,20 @@ and then calls and conversions. The remaining precedence levels are as follows
(in increasing precedence order):
Precedence Operator
1 ||
2 &&
3 == != < <= > >=
4 + - | ^
5 * / % << >> &
6 + - ! ^ < > * & (unary)
1 ||
2 &&
3 == != < <= > >=
4 + - | ^
5 * / % << >> &
6 + - ! ^ < > * & (unary)
For integer values, / and % satisfy the following relationship:
(a / b) * b + a % b == a
(a / b) * b + a % b == a
and
(a / b) is "truncated towards zero".
(a / b) is "truncated towards zero".
There are no implicit type conversions except for
constants and literals. In particular, unsigned and signed integer
......@@ -1123,12 +1123,12 @@ shift counts are undefined. Unary '^' corresponds to C '~' (bitwise
complement).
There is no '->' operator. Given a pointer p to a struct, one writes
p.f
p.f
to access field f of the struct. Similarly, given an array or map
pointer, one writes
p[i]
p[i]
to access an element. Given a function pointer, one writes
p()
p()
to call the function.
Other operators behave as in C.
......@@ -1508,32 +1508,32 @@ clause matches that of the dynamic value to be exchanged.
If multiple cases can proceed, a uniform fair choice is made regarding
which single communication will execute.
var c, c1, c2 *chan int;
select {
case i1 = <c1:
printf("received %d from c1\n", i1);
case >c2 = i2:
printf("sent %d to c2\n", i2);
default:
printf("no communication\n");
}
for { // send random sequence of bits to c
select {
case >c = 0: // note: no statement, no fallthrough, no folding of cases
case >c = 1:
}
}
var c, c1, c2 *chan int;
select {
case i1 = <c1:
printf("received %d from c1\n", i1);
case >c2 = i2:
printf("sent %d to c2\n", i2);
default:
printf("no communication\n");
}
var ca *chan any;
var i int;
var f float;
for { // send random sequence of bits to c
select {
case i = <ca:
printf("received int %d from ca\n", i);
case f = <ca:
printf("received float %f from ca\n", f);
case >c = 0: // note: no statement, no fallthrough, no folding of cases
case >c = 1:
}
}
var ca *chan any;
var i int;
var f float;
select {
case i = <ca:
printf("received int %d from ca\n", i);
case f = <ca:
printf("received float %f from ca\n", f);
}
TODO: do we allow case i := <c: ?
TODO: need to precise about all the details but this is not the right doc for that
......@@ -1658,9 +1658,9 @@ Executing the goto statement must not cause any variables to come into
scope that were not already in scope at the point of the goto. For
instance, this example:
goto L; // BAD
v := 3;
L:
goto L; // BAD
v := 3;
L:
is erroneous because the jump to label L skips the creation of v.
......@@ -1732,5 +1732,5 @@ TODO
- TODO: type switch?
- TODO: words about slices
- TODO: what is nil? do we type-test by a nil conversion or something else?
- TODO: I (gri) would like to say that sizeof(int) == sizeof(pointer), always.
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