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Diffstat (limited to 'src/go/token/token.go')
| -rw-r--r-- | src/go/token/token.go | 340 |
1 files changed, 340 insertions, 0 deletions
diff --git a/src/go/token/token.go b/src/go/token/token.go new file mode 100644 index 0000000..96a1079 --- /dev/null +++ b/src/go/token/token.go @@ -0,0 +1,340 @@ +// 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) +} |