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synced 2024-11-05 18:36:08 +00:00
- ripped out excessively fancy way of describing grammar
in favor of explicit constructs - simpler, clearer, and shorter overall - no spec changes (in retrospect it was just a (my) mistake to put it in in the first place) R=r DELTA=55 (13 added, 28 deleted, 14 changed) OCL=21434 CL=21462
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@ -3,7 +3,7 @@ The Go Programming Language Specification (DRAFT)
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Robert Griesemer, Rob Pike, Ken Thompson
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(December 16, 2008)
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(December 17, 2008)
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----
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@ -358,30 +358,26 @@ language support.
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Notation
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----
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The syntax is specified using Parameterized Extended Backus-Naur Form (PEBNF).
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Specifically, productions are expressions constructed from terms and the
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following operators:
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The syntax is specified using Extended Backus-Naur Form (EBNF):
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- | separates alternatives (least binding strength)
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- () groups
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- [] specifies an option (0 or 1 times)
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- {} specifies repetition (0 to n times)
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The syntax of PEBNF can be expressed in itself:
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Production = production_name [ Parameters ] "=" Expression .
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Parameters = "<" production_name { "," production_name } ">" .
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Production = production_name "=" Expression .
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Expression = Alternative { "|" Alternative } .
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Alternative = Term { Term } .
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Term = production_name [ Arguments ] | token [ "..." token ] | Group | Option | Repetition .
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Arguments = "<" Expression { "," Expression } ">" .
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Term = production_name | token [ "..." token ] | Group | Option | Repetition .
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Group = "(" Expression ")" .
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Option = "[" Expression ")" .
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Repetition = "{" Expression "}" .
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Productions are expressions constructed from terms and the following operators:
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| separates alternatives (least binding strength)
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() groups
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[] specifies an option (0 or 1 times)
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{} specifies repetition (0 to n times)
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Lower-case production names are used to identify productions that cannot
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be broken by white space or comments; they are usually tokens. Other
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production names are in CamelCase.
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be broken by white space or comments; they are tokens. Other production
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names are in CamelCase.
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Tokens (lexical symbols) are enclosed in double quotes '''' (the
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double quote symbol is written as ''"'').
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@ -389,15 +385,6 @@ double quote symbol is written as ''"'').
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The form "a ... b" represents the set of characters from "a" through "b" as
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alternatives.
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Productions can be parameterized. To get the actual production the parameter is
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substituted with the argument provided where the production name is used. For
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instance, there are various forms of semicolon-separated lists in the grammar.
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The parameterized production for such lists is:
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List<P> = P { ";" P } [ ";" ] .
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In this case, P stands for the actual list element.
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Where possible, recursive productions are used to express evaluation order
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and operator precedence syntactically (for instance for expressions).
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@ -684,14 +671,6 @@ function, method) and specifies properties of that entity such as its type.
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[ "export" | "package" ]
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( ConstDecl | TypeDecl | VarDecl | FunctionDecl | MethodDecl ) .
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Except for function, method and abbreviated variable declarations (using ":="),
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all declarations follow the same pattern. There is either a single declaration
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of the form P, or an optional semicolon-separated list of declarations of the
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form P surrounded by parentheses:
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Decl<P> = P | "(" [ List<P> ] ")" .
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List<P> = P { ";" P } [ ";" ] .
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Every identifier in a program must be declared; some identifiers, such as "int"
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and "true", are predeclared (§Predeclared identifiers).
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@ -796,7 +775,8 @@ Const declarations
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A constant declaration binds an identifier to the value of a constant
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expression (§Constant expressions).
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ConstDecl = "const" Decl<ConstSpec> .
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ConstDecl = "const" ( ConstSpec | "(" [ ConstSpecList ] ")" ) .
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ConstSpecList = ConstSpec { ";" ConstSpec } [ ";" ] .
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ConstSpec = IdentifierList [ CompleteType ] [ "=" ExpressionList ] .
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IdentifierList = identifier { "," identifier } .
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@ -949,7 +929,8 @@ Type declarations
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A type declaration specifies a new type and binds an identifier to it.
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The identifier is called the ``type name''; it denotes the type.
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TypeDecl = "type" Decl<TypeSpec> .
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TypeDecl = "type" ( TypeSpec | "(" [ TypeSpecList ] ")" ) .
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TypeSpecList = TypeSpec { ";" TypeSpec } [ ";" ] .
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TypeSpec = identifier Type .
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A struct or interface type may be forward-declared (§Struct types,
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@ -983,7 +964,8 @@ The variable type must be a complete type (§Types).
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In some forms of declaration the type of the initial value defines the type
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of the variable.
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VarDecl = "var" Decl<VarSpec> .
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VarDecl = "var" ( VarSpec | "(" [ VarSpecList ] ")" ) .
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VarSpecList = VarSpec { ";" VarSpec } [ ";" ] .
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VarSpec = IdentifierList ( CompleteType [ "=" ExpressionList ] | "=" ExpressionList ) .
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var i int
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@ -1007,7 +989,7 @@ If the variable type is omitted, and the corresponding initialization expression
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is a constant expression of abstract int or floating point type, the type
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of the variable is "int" or "float" respectively:
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var i = 0 // i has int type
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var i = 0 // i has int type
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var f = 3.1415 // f has float type
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The syntax
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@ -1344,7 +1326,8 @@ an identifier and type for each field. Within a struct type no field
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identifier may be declared twice and all field types must be complete
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types (§Types).
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StructType = "struct" [ "{" [ List<FieldDecl> ] "}" ] .
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StructType = "struct" [ "{" [ FieldDeclList ] "}" ] .
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FieldDeclList = FieldDecl { ";" FieldDecl } [ ";" ] .
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FieldDecl = (IdentifierList CompleteType | TypeName) [ Tag ] .
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Tag = string_lit .
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@ -1553,7 +1536,8 @@ Type interfaces may be specified explicitly by interface types.
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An interface type denotes the set of all types that implement at least
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the set of methods specified by the interface type, and the value "nil".
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InterfaceType = "interface" [ "{" [ List<MethodSpec> ] "}" ] .
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InterfaceType = "interface" [ "{" [ MethodSpecList ] "}" ] .
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MethodSpecList = MethodSpec { ";" MethodSpec } [ ";" ] .
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MethodSpec = IdentifierList FunctionType .
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// A basic file interface.
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A package can gain access to exported items from another package
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through an import declaration:
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ImportDecl = "import" Decl<ImportSpec> .
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ImportDecl = "import" ( ImportSpec | "(" [ ImportSpecList ] ")" ) .
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ImportSpecList = ImportSpec { ";" ImportSpec } [ ";" ] .
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ImportSpec = [ "." | PackageName ] PackageFileName .
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An import statement makes the exported contents of the named
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