[16620] | 1 | package symexpr
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| 2 |
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| 3 | import (
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| 4 | "fmt"
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| 5 | "strings"
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| 6 | "unicode"
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| 7 | "unicode/utf8"
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| 8 | )
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| 9 |
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| 10 | func (l *lexer) run() {
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| 11 | for state := lexExpr; state != nil; {
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| 12 | state = state(l)
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| 13 | }
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| 14 | l.items <- item{itemEOF, "eof"}
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| 15 | close(l.items) // No more tokens will be delivered.
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| 16 | }
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| 17 |
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| 18 | type item struct {
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| 19 | typ itemType
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| 20 | val string
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| 21 | }
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| 22 |
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| 23 | func (i item) String() string {
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| 24 | switch i.typ {
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| 25 | case itemEOF:
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| 26 | return "EOF"
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| 27 | case itemError:
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| 28 | return i.val
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| 29 | }
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| 30 | if len(i.val) > 10 {
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| 31 | return fmt.Sprintf("%.10q...", i.val)
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| 32 | }
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| 33 | return fmt.Sprintf("%d-'%s'", i.typ, i.val)
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| 34 | }
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| 35 |
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| 36 | type itemType int
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| 37 |
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| 38 | const (
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| 39 | itemNil itemType = iota
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| 40 | itemError
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| 41 | itemEOF // EOF
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| 42 |
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| 43 | itemAdd // +
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| 44 | itemMul // *
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| 45 | itemDiv // /
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| 46 | itemDiv2 // {...}//{...}
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| 47 | itemNeg // -
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| 48 | itemLParen // (
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| 49 | itemRParen // )
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| 50 | itemLBrack // {
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| 51 | itemRBrack // }
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| 52 | itemCarrot // ^
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| 53 |
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| 54 | itemNumber
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| 55 | itemIndex
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| 56 | itemIdentifier // vars,coeffs,funcs
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| 57 |
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| 58 | itemKeyword // placeholder
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| 59 | itemFrac // \frac
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| 60 | itemCDot // \cdot (latex multiplication)
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| 61 | itemSin
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| 62 | itemCos
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| 63 | itemTan
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| 64 | itemAbs
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| 65 | itemSqrt
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| 66 | itemExp
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| 67 | itemLog
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| 68 | )
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| 69 |
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| 70 | func isLeaf(it itemType) bool {
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| 71 | switch it {
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| 72 | case itemNumber, itemIdentifier:
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| 73 | return true
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| 74 | }
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| 75 | return false
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| 76 | }
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| 77 | func isUnary(it itemType) bool {
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| 78 | // switch it {
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| 79 | // case itemNeg:
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| 80 | // return true
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| 81 | // }
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| 82 | return false
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| 83 | }
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| 84 | func isBinary(it itemType) bool {
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| 85 | switch it {
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| 86 | case itemAdd, itemNeg, itemMul, itemDiv, itemDiv2, itemCarrot:
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| 87 | return true
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| 88 | }
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| 89 | return false
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| 90 | }
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| 91 |
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| 92 | var itemName = map[itemType]string{
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| 93 | itemNil: "nil",
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| 94 | itemError: "error",
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| 95 | itemEOF: "EOF",
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| 96 |
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| 97 | itemAdd: "add",
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| 98 | itemMul: "mul",
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| 99 | itemDiv: "div",
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| 100 | itemDiv2: "div2",
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| 101 | itemNeg: "neg",
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| 102 | itemLParen: "lParen",
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| 103 | itemRParen: "rParen",
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| 104 | itemLBrack: "lBrack",
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| 105 | itemRBrack: "rBrack",
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| 106 | itemCarrot: "carrot",
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| 107 |
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| 108 | itemNumber: "number",
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| 109 | itemIndex: "index",
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| 110 | itemIdentifier: "identifier",
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| 111 |
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| 112 | // keywords
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| 113 | itemCDot: "cdot",
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| 114 | itemFrac: "frac",
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| 115 | itemSin: "sin",
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| 116 | itemCos: "cos",
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| 117 | itemTan: "tan",
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| 118 | itemAbs: "abs",
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| 119 | itemSqrt: "sqrt",
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| 120 | itemExp: "exp",
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| 121 | itemLog: "ln",
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| 122 | }
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| 123 |
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| 124 | func (i itemType) String() string {
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| 125 | s := itemName[i]
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| 126 | if s == "" {
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| 127 | return fmt.Sprintf("item%d", int(i))
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| 128 | }
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| 129 | return s
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| 130 | }
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| 131 |
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| 132 | var key = map[string]itemType{
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| 133 | "\\cdot": itemCDot,
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| 134 | "\\frac": itemFrac,
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| 135 | "sin": itemSin,
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| 136 | "Sin": itemSin,
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| 137 | "cos": itemCos,
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| 138 | "Cos": itemCos,
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| 139 | "tan": itemTan,
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| 140 | "Tan": itemTan,
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| 141 | "abs": itemAbs,
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| 142 | "Abs": itemAbs,
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| 143 | "sqrt": itemSqrt,
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| 144 | "Sqrt": itemSqrt,
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| 145 | "e": itemExp,
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| 146 | "exp": itemExp,
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| 147 | "Exp": itemExp,
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| 148 | "ln": itemLog,
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| 149 | }
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| 150 |
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| 151 | const eof = -1
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| 152 |
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| 153 | // stateFn represents the state of the scanner as a function that returns the next state.
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| 154 | type stateFn func(*lexer) stateFn
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| 155 |
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| 156 | // lexer holds the state of the scanner.
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| 157 | type lexer struct {
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| 158 | name string // used only for error reports.
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| 159 | input string // the string being scanned.
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| 160 | vars []string // allowable variables
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| 161 | state stateFn // the next lexing function to enter.
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| 162 | start int // start position of this item.
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| 163 | pos int // current position in the input.
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| 164 | width int // width of last rune read from input.
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| 165 | items chan item // channel of scanned items.
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| 166 | nextToken item
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| 167 | }
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| 168 |
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| 169 | // next returns the next rune in the input.
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| 170 | func (l *lexer) next() (r rune) {
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| 171 | if l.pos >= len(l.input) {
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| 172 | l.width = 0
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| 173 | return eof
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| 174 | }
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| 175 | r, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
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| 176 | l.pos += l.width
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| 177 | return r
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| 178 | }
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| 179 |
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| 180 | // peek returns but does not consume the next rune in the input.
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| 181 | func (l *lexer) peek() rune {
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| 182 | r := l.next()
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| 183 | l.backup()
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| 184 | return r
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| 185 | }
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| 186 |
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| 187 | // backup steps back one rune. Can only be called once per call of next.
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| 188 | func (l *lexer) backup() {
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| 189 | l.pos -= l.width
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| 190 | }
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| 191 |
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| 192 | // emit passes an item back to the client.
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| 193 | func (l *lexer) emit(t itemType) {
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| 194 | l.items <- item{t, l.input[l.start:l.pos]}
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| 195 | l.start = l.pos
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| 196 | }
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| 197 |
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| 198 | // ignore skips over the pending input before this point.
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| 199 | func (l *lexer) ignore() {
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| 200 | l.start = l.pos
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| 201 | }
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| 202 |
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| 203 | // accept consumes the next rune if it's from the valid set.
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| 204 | func (l *lexer) accept(valid string) bool {
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| 205 | if strings.IndexRune(valid, l.next()) >= 0 {
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| 206 | return true
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| 207 | }
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| 208 | l.backup()
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| 209 | return false
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| 210 | }
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| 211 |
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| 212 | // acceptRun consumes a run of runes from the valid set.
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| 213 | func (l *lexer) acceptRun(valid string) {
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| 214 | for strings.IndexRune(valid, l.next()) >= 0 {
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| 215 | }
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| 216 | l.backup()
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| 217 | }
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| 218 |
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| 219 | // lineNumber reports which line we're on. Doing it this way
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| 220 | // means we don't have to worry about peek double counting.
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| 221 | func (l *lexer) lineNumber() int {
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| 222 | return 1 + strings.Count(l.input[:l.pos], "\n")
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| 223 | }
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| 224 |
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| 225 | // error returns an error token and terminates the scan by passing
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| 226 | // back a nil pointer that will be the next state, terminating l.nextItem.
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| 227 | func (l *lexer) errorf(format string, args ...interface{}) stateFn {
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| 228 | l.items <- item{itemError, fmt.Sprintf(format, args...)}
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| 229 | return nil
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| 230 | }
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| 231 |
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| 232 | // nextItem returns the next item from the input.
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| 233 | func (l *lexer) nextItem() item {
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| 234 | for {
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| 235 | select {
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| 236 | case item := <-l.items:
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| 237 | return item
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| 238 | default:
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| 239 | l.state = l.state(l)
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| 240 | }
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| 241 | }
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| 242 | panic("not reached")
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| 243 | }
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| 244 |
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| 245 | // lex creates a new scanner for the input string.
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| 246 | func lex(name, input string, vars []string) *lexer {
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| 247 | l := &lexer{
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| 248 | name: name,
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| 249 | input: input,
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| 250 | vars: vars,
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| 251 | state: lexExpr,
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| 252 | items: make(chan item, 2), // Two items of buffering is sufficient for all state functions
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| 253 | }
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| 254 | return l
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| 255 | }
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| 256 |
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| 257 | /***** State Functions *****/
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| 258 |
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| 259 | // lexExpr is the top level scanner
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| 260 | func lexExpr(l *lexer) stateFn {
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| 261 | switch r := l.next(); {
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| 262 | case r == eof || r == '\n':
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| 263 | return nil
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| 264 | case isSpace(r):
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| 265 | l.ignore()
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| 266 | case r == '+':
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| 267 | l.emit(itemAdd)
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| 268 | return lexExpr
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| 269 | case r == '*':
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| 270 | l.emit(itemMul)
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| 271 | return lexExpr
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| 272 | case r == '^':
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| 273 | l.emit(itemCarrot)
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| 274 | return lexExpr
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| 275 | case r == '/':
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| 276 | if l.peek() == '/' {
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| 277 | l.emit(itemDiv2)
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| 278 | } else {
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| 279 | l.emit(itemDiv)
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| 280 | }
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| 281 | return lexExpr
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| 282 | case r == '-':
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| 283 | l.emit(itemNeg)
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| 284 | return lexExpr
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| 285 | case r == '(':
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| 286 | l.emit(itemLParen)
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| 287 | return lexExpr
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| 288 | case r == ')':
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| 289 | l.emit(itemRParen)
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| 290 | return lexExpr
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| 291 | case r == '{':
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| 292 | l.emit(itemLBrack)
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| 293 | return lexExpr
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| 294 | case r == '}':
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| 295 | l.emit(itemRBrack)
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| 296 | return lexExpr
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| 297 | case r == '\\':
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| 298 | // l.backup()
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| 299 | return lexIdentifier
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| 300 | case r == '_':
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| 301 | l.ignore()
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| 302 | return lexIndex
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| 303 | case '0' <= r && r <= '9':
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| 304 | l.backup()
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| 305 | return lexNumber
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| 306 | case isAlphaNumeric(r):
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| 307 | l.backup()
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| 308 | return lexIdentifier
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| 309 | default:
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| 310 | return l.errorf("unrecognized character in action: %#U", r)
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| 311 | }
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| 312 | return lexExpr
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| 313 | }
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| 314 |
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| 315 | // lexIdentifier scans an alphanumeric or field.
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| 316 | func lexIdentifier(l *lexer) stateFn {
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| 317 | Loop:
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| 318 | for {
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| 319 | switch r := l.next(); {
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| 320 | case isAlphaNumeric(r):
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| 321 | // absorb.
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| 322 | case r == '_':
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| 323 | // absorb and scanIndex
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| 324 | digits := "0123456789"
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| 325 | l.acceptRun(digits)
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| 326 | l.emit(itemIdentifier)
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| 327 | return lexExpr
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| 328 | case r == '.' && (l.input[l.start] == '.' || l.input[l.start] == '$'):
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| 329 | // field chaining; absorb into one token.
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| 330 | default:
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| 331 | l.backup()
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| 332 | word := l.input[l.start:l.pos]
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| 333 | if !l.atTerminator() {
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| 334 | return l.errorf("unexpected character %c", r)
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| 335 | }
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| 336 | switch {
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| 337 | case key[word] > itemKeyword:
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| 338 | l.emit(key[word])
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| 339 | default:
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| 340 | l.emit(itemIdentifier)
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| 341 | }
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| 342 | break Loop
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| 343 | }
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| 344 | }
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| 345 | return lexExpr
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| 346 | }
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| 347 |
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| 348 | // atTerminator reports whether the input is at valid termination character to
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| 349 | // appear after an identifier. Mostly to catch cases like "$x+2" not being
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| 350 | // acceptable without a space, in case we decide one day to implement
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| 351 | // arithmetic.
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| 352 | func (l *lexer) atTerminator() bool {
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| 353 | r := l.peek()
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| 354 | if isSpace(r) {
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| 355 | return true
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| 356 | }
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| 357 | switch r {
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| 358 | case eof, '+', '-', '(', ')', '{', '}', '/', '*', '^':
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| 359 | return true
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| 360 | }
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| 361 | return false
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| 362 | }
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| 363 |
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| 364 | // lexNumber scans a number: decimal, octal, hex, float, or imaginary. This
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| 365 | // isn't a perfect number scanner - for instance it accepts "." and "0x0.2"
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| 366 | // and "089" - but when it's wrong the input is invalid and the parser (via
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| 367 | // strconv) will notice.
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| 368 | func lexNumber(l *lexer) stateFn {
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| 369 | if !l.scanNumber() {
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| 370 | return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
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| 371 | } else {
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| 372 | l.emit(itemNumber)
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| 373 | }
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| 374 | return lexExpr
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| 375 | }
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| 376 |
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| 377 | func lexIndex(l *lexer) stateFn {
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| 378 | if !l.scanIndex() {
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| 379 | return l.errorf("bad index syntax: %q", l.input[l.start:l.pos])
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| 380 | } else {
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| 381 | l.emit(itemIndex)
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| 382 | }
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| 383 | return lexExpr
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| 384 | }
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| 385 |
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| 386 | func (l *lexer) scanIndex() bool {
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| 387 | // Optional leading sign.
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| 388 | digits := "0123456789"
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| 389 | l.acceptRun(digits)
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| 390 |
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| 391 | // Next thing mustn't be alphanumeric.
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| 392 | // if isAlphaNumeric(l.peek()) {
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| 393 | // l.next()
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| 394 | // return false
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| 395 | // }
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| 396 | return true
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| 397 | }
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| 398 |
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| 399 | func (l *lexer) scanNumber() bool {
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| 400 | // Optional leading sign.
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| 401 | l.accept("+-")
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| 402 | digits := "0123456789"
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| 403 | l.acceptRun(digits)
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| 404 | if l.accept(".") {
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| 405 | l.acceptRun(digits)
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| 406 | }
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| 407 | if l.accept("eE") {
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| 408 | l.accept("+-")
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| 409 | l.acceptRun("0123456789")
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| 410 | }
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| 411 | // Is it imaginary?
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| 412 | l.accept("i")
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| 413 | // Next thing mustn't be alphanumeric.
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| 414 | // if isAlphaNumeric(l.peek()) {
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| 415 | // l.next()
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| 416 | // return false
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| 417 | // }
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| 418 | return true
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| 419 | }
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| 420 |
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| 421 | // isSpace reports whether r is a space character.
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| 422 | func isSpace(r rune) bool {
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| 423 | switch r {
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| 424 | case ' ', '\t', '\n', '\r':
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| 425 | return true
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| 426 | }
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| 427 | return false
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| 428 | }
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| 429 |
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| 430 | // isAlphaNumeric reports whether r is an alphabetic or digit
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| 431 | func isAlphaNumeric(r rune) bool {
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| 432 | return unicode.IsLetter(r) || unicode.IsDigit(r)
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| 433 | }
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