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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package token defines constants representing the lexical tokens of the Go
// programming language and basic operations on tokens (printing, predicates).
//
package token
import (
"strconv"
"unicode"
"unicode/utf8"
)
// Token is the set of lexical tokens of the Go programming language.
type Token int
// The list of tokens.
const (
// Special tokens
ILLEGAL Token = iota
EOF
COMMENT
literal_beg
// Identifiers and basic type literals
// (these tokens stand for classes of literals)
IDENT // main
INT // 12345
FLOAT // 123.45
IMAG // 123.45i
CHAR // 'a'
STRING // "abc"
literal_end
operator_beg
// Operators and delimiters
ADD // +
SUB // -
MUL // *
QUO // /
REM // %
AND // &
OR // |
XOR // ^
SHL // <<
SHR // >>
AND_NOT // &^
ADD_ASSIGN // +=
SUB_ASSIGN // -=
MUL_ASSIGN // *=
QUO_ASSIGN // /=
REM_ASSIGN // %=
AND_ASSIGN // &=
OR_ASSIGN // |=
XOR_ASSIGN // ^=
SHL_ASSIGN // <<=
SHR_ASSIGN // >>=
AND_NOT_ASSIGN // &^=
LAND // &&
LOR // ||
ARROW // <-
INC // ++
DEC // --
EQL // ==
LSS // <
GTR // >
ASSIGN // =
NOT // !
NEQ // !=
LEQ // <=
GEQ // >=
DEFINE // :=
ELLIPSIS // ...
LPAREN // (
LBRACK // [
LBRACE // {
COMMA // ,
PERIOD // .
RPAREN // )
RBRACK // ]
RBRACE // }
SEMICOLON // ;
COLON // :
operator_end
keyword_beg
// Keywords
BREAK
CASE
CHAN
CONST
CONTINUE
DEFAULT
DEFER
ELSE
FALLTHROUGH
FOR
FUNC
GO
GOTO
IF
IMPORT
INTERFACE
MAP
PACKAGE
RANGE
RETURN
SELECT
STRUCT
SWITCH
TYPE
VAR
keyword_end
)
var tokens = [...]string{
ILLEGAL: "ILLEGAL",
EOF: "EOF",
COMMENT: "COMMENT",
IDENT: "IDENT",
INT: "INT",
FLOAT: "FLOAT",
IMAG: "IMAG",
CHAR: "CHAR",
STRING: "STRING",
ADD: "+",
SUB: "-",
MUL: "*",
QUO: "/",
REM: "%",
AND: "&",
OR: "|",
XOR: "^",
SHL: "<<",
SHR: ">>",
AND_NOT: "&^",
ADD_ASSIGN: "+=",
SUB_ASSIGN: "-=",
MUL_ASSIGN: "*=",
QUO_ASSIGN: "/=",
REM_ASSIGN: "%=",
AND_ASSIGN: "&=",
OR_ASSIGN: "|=",
XOR_ASSIGN: "^=",
SHL_ASSIGN: "<<=",
SHR_ASSIGN: ">>=",
AND_NOT_ASSIGN: "&^=",
LAND: "&&",
LOR: "||",
ARROW: "<-",
INC: "++",
DEC: "--",
EQL: "==",
LSS: "<",
GTR: ">",
ASSIGN: "=",
NOT: "!",
NEQ: "!=",
LEQ: "<=",
GEQ: ">=",
DEFINE: ":=",
ELLIPSIS: "...",
LPAREN: "(",
LBRACK: "[",
LBRACE: "{",
COMMA: ",",
PERIOD: ".",
RPAREN: ")",
RBRACK: "]",
RBRACE: "}",
SEMICOLON: ";",
COLON: ":",
BREAK: "break",
CASE: "case",
CHAN: "chan",
CONST: "const",
CONTINUE: "continue",
DEFAULT: "default",
DEFER: "defer",
ELSE: "else",
FALLTHROUGH: "fallthrough",
FOR: "for",
FUNC: "func",
GO: "go",
GOTO: "goto",
IF: "if",
IMPORT: "import",
INTERFACE: "interface",
MAP: "map",
PACKAGE: "package",
RANGE: "range",
RETURN: "return",
SELECT: "select",
STRUCT: "struct",
SWITCH: "switch",
TYPE: "type",
VAR: "var",
}
// String returns the string corresponding to the token tok.
// For operators, delimiters, and keywords the string is the actual
// token character sequence (e.g., for the token ADD, the string is
// "+"). For all other tokens the string corresponds to the token
// constant name (e.g. for the token IDENT, the string is "IDENT").
//
func (tok Token) String() string {
s := ""
if 0 <= tok && tok < Token(len(tokens)) {
s = tokens[tok]
}
if s == "" {
s = "token(" + strconv.Itoa(int(tok)) + ")"
}
return s
}
// A set of constants for precedence-based expression parsing.
// Non-operators have lowest precedence, followed by operators
// starting with precedence 1 up to unary operators. The highest
// precedence serves as "catch-all" precedence for selector,
// indexing, and other operator and delimiter tokens.
//
const (
LowestPrec = 0 // non-operators
UnaryPrec = 6
HighestPrec = 7
)
// Precedence returns the operator precedence of the binary
// operator op. If op is not a binary operator, the result
// is LowestPrecedence.
//
func (op Token) Precedence() int {
switch op {
case LOR:
return 1
case LAND:
return 2
case EQL, NEQ, LSS, LEQ, GTR, GEQ:
return 3
case ADD, SUB, OR, XOR:
return 4
case MUL, QUO, REM, SHL, SHR, AND, AND_NOT:
return 5
}
return LowestPrec
}
var keywords map[string]Token
func init() {
keywords = make(map[string]Token)
for i := keyword_beg + 1; i < keyword_end; i++ {
keywords[tokens[i]] = i
}
}
// Lookup maps an identifier to its keyword token or IDENT (if not a keyword).
//
func Lookup(ident string) Token {
if tok, is_keyword := keywords[ident]; is_keyword {
return tok
}
return IDENT
}
// Predicates
// IsLiteral returns true for tokens corresponding to identifiers
// and basic type literals; it returns false otherwise.
//
func (tok Token) IsLiteral() bool { return literal_beg < tok && tok < literal_end }
// IsOperator returns true for tokens corresponding to operators and
// delimiters; it returns false otherwise.
//
func (tok Token) IsOperator() bool { return operator_beg < tok && tok < operator_end }
// IsKeyword returns true for tokens corresponding to keywords;
// it returns false otherwise.
//
func (tok Token) IsKeyword() bool { return keyword_beg < tok && tok < keyword_end }
// IsExported reports whether name starts with an upper-case letter.
//
func IsExported(name string) bool {
ch, _ := utf8.DecodeRuneInString(name)
return unicode.IsUpper(ch)
}
// IsKeyword reports whether name is a Go keyword, such as "func" or "return".
//
func IsKeyword(name string) bool {
// TODO: opt: use a perfect hash function instead of a global map.
_, ok := keywords[name]
return ok
}
// IsIdentifier reports whether name is a Go identifier, that is, a non-empty
// string made up of letters, digits, and underscores, where the first character
// is not a digit. Keywords are not identifiers.
//
func IsIdentifier(name string) bool {
for i, c := range name {
if !unicode.IsLetter(c) && c != '_' && (i == 0 || !unicode.IsDigit(c)) {
return false
}
}
return name != "" && !IsKeyword(name)
}
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