several changes:

1. moved scan/symbol.go to new package sym and adapted all files that reference Symbol type and its values.
2. new type interval defined by begin, end and step values.
3. replaced operator-range.go with operator-interval.go.
4. replaced range operator begin:end with begin..end..step.
5. new implementation of sub-collection extraction based on new interval literal.

scan/scanner.go

@@ -12,20 +12,23 @@ import (
 	"strconv"
 	"strings"
 
+	"git.portale-stac.it/go-pkg/expr/sym"
 	"git.portale-stac.it/go-pkg/expr/util"
 )
 
 type Scanner struct {
-	current      *Token
-	prev         *Token
-	stage        *Token
-	stream       *bufio.Reader
-	row          int
-	column       int
-	translations map[Symbol]Symbol
+	current       *Token
+	prev          *Token
+	stage         *Token
+	stream        *bufio.Reader
+	row           int
+	column        int
+	translations  map[sym.Symbol]sym.Symbol
+	unreadByte    byte
+	prevRowLength int
 }
 
-func NewScanner(s io.Reader, translations map[Symbol]Symbol) (inst *Scanner) {
+func NewScanner(s io.Reader, translations map[sym.Symbol]sym.Symbol) (inst *Scanner) {
 	inst = &Scanner{
 		stream:       bufio.NewReader(s),
 		row:          1,
@@ -36,15 +39,15 @@ func NewScanner(s io.Reader, translations map[Symbol]Symbol) (inst *Scanner) {
 	return inst
 }
 
-func DefaultTranslations() map[Symbol]Symbol {
-	return map[Symbol]Symbol{
-		SymDoubleAmpersand: SymAnd,
-		SymKwAnd:           SymAnd,
-		SymDoubleVertBar:   SymOr,
-		SymKwOr:            SymOr,
-		// SymTilde:           SymNot,
-		SymKwNot:       SymNot,
-		SymLessGreater: SymNotEqual,
+func DefaultTranslations() map[sym.Symbol]sym.Symbol {
+	return map[sym.Symbol]sym.Symbol{
+		sym.SymDoubleAmpersand: sym.SymAnd,
+		sym.SymKwAnd:           sym.SymAnd,
+		sym.SymDoubleVertBar:   sym.SymOr,
+		sym.SymKwOr:            sym.SymOr,
+		sym.SymKwNot:           sym.SymNot,
+		sym.SymLessGreater:     sym.SymNotEqual,
+		// SymTilde:           sym.SymNot,
 	}
 }
 
@@ -56,9 +59,25 @@ func (scanner *Scanner) Current() *Token {
 	return scanner.current
 }
 
+func (scanner *Scanner) setUnreadChar(ch byte) {
+	scanner.column--
+	if scanner.column == 0 {
+		scanner.column = scanner.prevRowLength
+		scanner.row--
+	}
+	scanner.unreadByte = ch
+}
+
 func (scanner *Scanner) readChar() (ch byte, err error) {
-	if ch, err = scanner.stream.ReadByte(); err == nil {
+	if scanner.unreadByte != 0 {
+		ch = scanner.unreadByte
+		scanner.unreadByte = 0
+	} else {
+		ch, err = scanner.stream.ReadByte()
+	}
+	if err == nil {
 		if ch == '\n' {
+			scanner.prevRowLength = scanner.column
 			scanner.row++
 			scanner.column = 0
 		} else {
@@ -127,237 +146,237 @@ func (scanner *Scanner) fetchNextToken() (tk *Token) {
 		switch ch {
 		case '+':
 			if next, _ := scanner.peek(); next == '+' {
-				tk = scanner.moveOn(SymDoublePlus, ch, next)
+				tk = scanner.moveOn(sym.SymDoublePlus, ch, next)
 			} else if next == '=' {
-				tk = scanner.moveOn(SymPlusEqual, ch, next)
+				tk = scanner.moveOn(sym.SymPlusEqual, ch, next)
 			} else if next == '>' {
-				tk = scanner.moveOn(SymPlusGreater, ch, next)
+				tk = scanner.moveOn(sym.SymPlusGreater, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymPlus, ch)
+				tk = scanner.MakeToken(sym.SymPlus, ch)
 			}
 		case '-':
 			if next, _ := scanner.peek(); next == '-' {
-				tk = scanner.moveOn(SymDoubleMinus, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleMinus, ch, next)
 			} else if next == '=' {
-				tk = scanner.moveOn(SymMinusEqual, ch, next)
+				tk = scanner.moveOn(sym.SymMinusEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymMinus, ch)
+				tk = scanner.MakeToken(sym.SymMinus, ch)
 			}
 		case '*':
 			if next, _ := scanner.peek(); next == '*' {
-				tk = scanner.moveOn(SymDoubleStar, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleStar, ch, next)
 				// } else if next == '/' {
 				// 	tk = self.moveOn(SymClosedComment, ch, next)
 			} else if next, _ = scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymStarEqual, ch, next)
+				tk = scanner.moveOn(sym.SymStarEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymStar, ch)
+				tk = scanner.MakeToken(sym.SymStar, ch)
 			}
 		case '/':
 			if next, _ := scanner.peek(); next == '*' {
 				scanner.readChar()
 				tk = scanner.fetchBlockComment()
 			} else if next, _ = scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymSlashEqual, ch, next)
+				tk = scanner.moveOn(sym.SymSlashEqual, ch, next)
 			} else if next == '/' {
 				scanner.readChar()
 				tk = scanner.fetchOnLineComment()
 			} else {
-				tk = scanner.MakeToken(SymSlash, ch)
+				tk = scanner.MakeToken(sym.SymSlash, ch)
 			}
 		case '\\':
 			if escape {
-				tk = scanner.MakeToken(SymBackSlash, ch)
+				tk = scanner.MakeToken(sym.SymBackSlash, ch)
 				escape = false
 			} else {
 				escape = true
 			}
 		case '|':
 			if next, _ := scanner.peek(); next == '|' {
-				tk = scanner.moveOn(SymDoubleVertBar, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleVertBar, ch, next)
 			} else if next, _ = scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymVertBarEqual, ch, next)
+				tk = scanner.moveOn(sym.SymVertBarEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymVertBar, ch)
+				tk = scanner.MakeToken(sym.SymVertBar, ch)
 			}
 		case ',':
-			tk = scanner.MakeToken(SymComma, ch)
+			tk = scanner.MakeToken(sym.SymComma, ch)
 		case '^':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymCaretEqual, ch, next)
+				tk = scanner.moveOn(sym.SymCaretEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymCaret, ch)
+				tk = scanner.MakeToken(sym.SymCaret, ch)
 			}
 		case ':':
 			if next, _ := scanner.peek(); next == ':' {
-				tk = scanner.moveOn(SymDoubleColon, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleColon, ch, next)
 			} else if next == '=' {
-				tk = scanner.moveOn(SymColonEqual, ch, next)
+				tk = scanner.moveOn(sym.SymColonEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymColon, ch)
+				tk = scanner.MakeToken(sym.SymColon, ch)
 			}
 		case ';':
-			tk = scanner.MakeToken(SymSemiColon, ch)
+			tk = scanner.MakeToken(sym.SymSemiColon, ch)
 		case '.':
 			//if next, _ := self.peek(); next >= '0' && next <= '9' {
 			//	tk = self.parseNumber(ch)
 			//} else if next == '/' {
 			if next, _ := scanner.peek(); next == '/' {
-				tk = scanner.moveOn(SymDotSlash, ch, next)
+				tk = scanner.moveOn(sym.SymDotSlash, ch, next)
 			} else if next == '.' {
+				tk = scanner.moveOn(sym.SymDoubleDot, ch, next)
+				// TODO: this section needs verification
 				if next1, _ := scanner.peek(); next1 == '.' {
-					tk = scanner.moveOn(SymTripleDot, ch, next, next1)
-				} else {
-					tk = scanner.moveOn(SymDoubleDot, ch, next)
+					tk = scanner.moveOn(sym.SymTripleDot, next, next1)
 				}
 			} else {
-				tk = scanner.MakeToken(SymDot, ch)
+				tk = scanner.MakeToken(sym.SymDot, ch)
 			}
 		case '\'':
 			if escape {
-				tk = scanner.MakeToken(SymQuote, ch)
+				tk = scanner.MakeToken(sym.SymQuote, ch)
 				escape = false
 			} else {
 				tk = scanner.fetchString(ch, true)
 			}
 		case '"':
 			if escape {
-				tk = scanner.MakeToken(SymDoubleQuote, ch)
+				tk = scanner.MakeToken(sym.SymDoubleQuote, ch)
 				escape = false
 			} else {
 				tk = scanner.fetchString(ch, true)
 			}
 		case '`':
-			tk = scanner.MakeToken(SymBackTick, ch)
+			tk = scanner.MakeToken(sym.SymBackTick, ch)
 		case '!':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymNotEqual, ch, next)
+				tk = scanner.moveOn(sym.SymNotEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymExclamation, ch)
+				tk = scanner.MakeToken(sym.SymExclamation, ch)
 			}
 		case '?':
 			if next, _ := scanner.peek(); next == '?' {
-				tk = scanner.moveOn(SymDoubleQuestion, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleQuestion, ch, next)
 			} else if next == '=' {
-				tk = scanner.moveOn(SymQuestionEqual, ch, next)
+				tk = scanner.moveOn(sym.SymQuestionEqual, ch, next)
 			} else if next == '!' {
-				tk = scanner.moveOn(SymQuestionExclam, ch, next)
+				tk = scanner.moveOn(sym.SymQuestionExclam, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymQuestion, ch)
+				tk = scanner.MakeToken(sym.SymQuestion, ch)
 			}
 		case '&':
 			if next, _ := scanner.peek(); next == '&' {
-				tk = scanner.moveOn(SymDoubleAmpersand, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleAmpersand, ch, next)
 			} else if next, _ = scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymAmpersandEqual, ch, next)
+				tk = scanner.moveOn(sym.SymAmpersandEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymAmpersand, ch)
+				tk = scanner.MakeToken(sym.SymAmpersand, ch)
 			}
 		case '%':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymPercEqual, ch, next)
+				tk = scanner.moveOn(sym.SymPercEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymPercent, ch)
+				tk = scanner.MakeToken(sym.SymPercent, ch)
 			}
 		case '#':
-			tk = scanner.MakeToken(SymHash, ch)
+			tk = scanner.MakeToken(sym.SymHash, ch)
 		case '@':
 			if next, _ := scanner.peek(); (next >= 'a' && next <= 'z') || (next >= 'A' && next <= 'Z') {
 				scanner.readChar()
-				if tk = scanner.fetchIdentifier(next); tk.Sym == SymIdentifier {
+				if tk = scanner.fetchIdentifier(next); tk.Sym == sym.SymIdentifier {
 					//tk.Sym = SymIdRef
 					tk.source = "@" + tk.source
 				} else {
 					tk = scanner.makeErrorToken(fmt.Errorf("invalid variable reference %q", tk.source))
 				}
 			} else if next == '@' {
-				tk = scanner.moveOn(SymDoubleAt, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleAt, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymAt, ch)
+				tk = scanner.MakeToken(sym.SymAt, ch)
 			}
 		case '_':
-			tk = scanner.MakeToken(SymUndescore, ch)
+			tk = scanner.MakeToken(sym.SymUndescore, ch)
 		case '=':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymDoubleEqual, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleEqual, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymEqual, ch)
+				tk = scanner.MakeToken(sym.SymEqual, ch)
 			}
 		case '<':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymLessOrEqual, ch, next)
+				tk = scanner.moveOn(sym.SymLessOrEqual, ch, next)
 			} else if next == '<' {
 				scanner.readChar()
 				next2, _ := scanner.readChar()
 				scanner.unreadChar()
 				if next2 == '=' {
-					tk = scanner.moveOn(SymDoubleLessEqual, ch, next, next2)
+					tk = scanner.moveOn(sym.SymDoubleLessEqual, ch, next, next2)
 				} else {
-					tk = scanner.accept(SymDoubleLess, ch, next)
+					tk = scanner.accept(sym.SymDoubleLess, ch, next)
 				}
 			} else if next == '>' {
-				tk = scanner.moveOn(SymLessGreater, ch, next)
+				tk = scanner.moveOn(sym.SymLessGreater, ch, next)
 			} else if next == '+' {
-				tk = scanner.moveOn(SymLessPlus, ch, next)
+				tk = scanner.moveOn(sym.SymLessPlus, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymLess, ch)
+				tk = scanner.MakeToken(sym.SymLess, ch)
 			}
 		case '>':
 			if next, _ := scanner.peek(); next == '=' {
-				tk = scanner.moveOn(SymGreaterOrEqual, ch, next)
+				tk = scanner.moveOn(sym.SymGreaterOrEqual, ch, next)
 			} else if next == '>' {
 				scanner.readChar()
 				next2, _ := scanner.readChar()
 				scanner.unreadChar()
 				if next2 == '=' {
-					tk = scanner.moveOn(SymDoubleGreaterEqual, ch, next, next2)
+					tk = scanner.moveOn(sym.SymDoubleGreaterEqual, ch, next, next2)
 				} else {
-					tk = scanner.accept(SymDoubleGreater, ch, next)
+					tk = scanner.accept(sym.SymDoubleGreater, ch, next)
 				}
 			} else if next == ']' {
-				tk = scanner.moveOn(SymGreaterClosedSquare, ch, next)
+				tk = scanner.moveOn(sym.SymGreaterClosedSquare, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymGreater, ch)
+				tk = scanner.MakeToken(sym.SymGreater, ch)
 			}
 		case '$':
 			if next, _ := scanner.peek(); next == '(' {
-				tk = scanner.moveOn(SymDollarRound, ch, next)
+				tk = scanner.moveOn(sym.SymDollarRound, ch, next)
 				tk.source += ")"
 			} else if next == '$' {
-				tk = scanner.moveOn(SymDoubleDollar, ch, next)
+				tk = scanner.moveOn(sym.SymDoubleDollar, ch, next)
 			} else if next == '{' {
 				scanner.readChar()
 				if tk = scanner.fetchString('}', false); tk != nil {
-					tk.Sym = SymIdentifier
+					tk.Sym = sym.SymIdentifier
 				}
 			} else if next == '_' || (next >= 'a' && next <= 'z') || (next >= 'A' && next <= 'Z') {
 				scanner.readChar()
 				tk = scanner.fetchIdentifier(next)
 			} else {
-				tk = scanner.MakeToken(SymDollar, ch)
+				tk = scanner.MakeToken(sym.SymDollar, ch)
 			}
 		case '(':
 			//			if next, _ := scanner.peek(); next == ')' {
 			//				tk = scanner.moveOn(SymOpenClosedRound, ch, next)
 			//			} else {
-			tk = scanner.MakeToken(SymOpenRound, ch)
+			tk = scanner.MakeToken(sym.SymOpenRound, ch)
 			//			}
 		case ')':
-			tk = scanner.MakeToken(SymClosedRound, ch)
+			tk = scanner.MakeToken(sym.SymClosedRound, ch)
 		case '[':
 			if next, _ := scanner.peek(); next == '<' {
-				tk = scanner.moveOn(SymOpenSquareLess, ch, next)
+				tk = scanner.moveOn(sym.SymOpenSquareLess, ch, next)
 			} else {
-				tk = scanner.MakeToken(SymOpenSquare, ch)
+				tk = scanner.MakeToken(sym.SymOpenSquare, ch)
 			}
 		case ']':
-			tk = scanner.MakeToken(SymClosedSquare, ch)
+			tk = scanner.MakeToken(sym.SymClosedSquare, ch)
 		case '{':
-			tk = scanner.MakeToken(SymOpenBrace, ch)
+			tk = scanner.MakeToken(sym.SymOpenBrace, ch)
 		case '}':
-			tk = scanner.MakeToken(SymClosedBrace, ch)
+			tk = scanner.MakeToken(sym.SymClosedBrace, ch)
 		case '~':
-			tk = scanner.MakeToken(SymTilde, ch)
+			tk = scanner.MakeToken(sym.SymTilde, ch)
 		case 0:
 			if escape {
 				tk = scanner.makeErrorToken(errors.New("incomplete escape sequence"))
@@ -365,9 +384,9 @@ func (scanner *Scanner) fetchNextToken() (tk *Token) {
 			escape = false
 		default:
 			if /*ch == '_' ||*/ (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') {
-				if tk = scanner.fetchIdentifier(ch); tk.Sym == SymKwFunc {
+				if tk = scanner.fetchIdentifier(ch); tk.Sym == sym.SymKwFunc {
 					if next, _ := scanner.peek(); next == '(' {
-						tk = scanner.moveOn(SymFuncDef, ch, next)
+						tk = scanner.moveOn(sym.SymFuncDef, ch, next)
 					}
 				}
 			} else if ch >= '0' && ch <= '9' {
@@ -415,19 +434,20 @@ func (scanner *Scanner) initBase(currentFirstCh byte) (firstCh byte, numBase int
 	numBase = 10
 
 	if ch, err = scanner.peek(); err == nil {
-		if ch == 'b' || ch == 'B' {
+		switch ch {
+		case 'b', 'B':
 			numBase = 2
 			digitType = "binary"
 			scanner.readChar()
 			digitFunc = isBinaryDigit
 			firstCh, err = scanner.readChar()
-		} else if ch == 'o' || ch == 'O' {
+		case 'o', 'O':
 			numBase = 8
 			digitType = "octal"
 			scanner.readChar()
 			digitFunc = isOctalDigit
 			firstCh, err = scanner.readChar()
-		} else if ch == 'x' || ch == 'X' {
+		case 'x', 'X':
 			numBase = 16
 			digitType = "hex"
 			scanner.readChar()
@@ -449,7 +469,7 @@ func (scanner *Scanner) initBase(currentFirstCh byte) (firstCh byte, numBase int
 func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 	var err error
 	var ch byte
-	var sym Symbol = SymInteger
+	var symbol sym.Symbol = sym.SymInteger
 	var sb strings.Builder
 	var isDigit func(byte) bool = isDecimalDigit
 	var numBase = 10
@@ -463,18 +483,24 @@ func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 
 	if numBase == 10 {
 		if err == nil && ch == '.' {
-			sym = SymFloat
-			sb.WriteByte(ch)
-			ch, err = scanner.readChar()
-			if ch >= '0' && ch <= '9' {
-				for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = scanner.readChar() {
-					sb.WriteByte(ch)
+			if next, _ := scanner.peek(); next == '.' {
+				// do nothing, this is an interval operator
+				scanner.setUnreadChar('.')
+			} else {
+				symbol = sym.SymFloat
+				sb.WriteByte(ch)
+				ch, err = scanner.readChar()
+				if ch >= '0' && ch <= '9' {
+					for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = scanner.readChar() {
+						sb.WriteByte(ch)
+					}
 				}
 			}
 		}
 		if err == nil {
-			if ch == 'e' || ch == 'E' {
-				sym = SymFloat
+			switch ch {
+			case 'e', 'E':
+				symbol = sym.SymFloat
 				sb.WriteByte(ch)
 				if ch, err = scanner.readChar(); err == nil {
 					if ch == '+' || ch == '-' {
@@ -489,8 +515,8 @@ func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 						err = fmt.Errorf("[%d:%d] expected integer exponent, got %c", scanner.row, scanner.column, ch)
 					}
 				}
-			} else if ch == '(' {
-				sym = SymFraction
+			case '(':
+				symbol = sym.SymFraction
 				sb.WriteByte(ch)
 				ch, err = scanner.readChar()
 				for ; err == nil && (ch >= '0' && ch <= '9'); ch, err = scanner.readChar() {
@@ -514,15 +540,16 @@ func (scanner *Scanner) parseNumber(firstCh byte) (tk *Token) {
 		var value any
 		_ = scanner.sync(err) // TODO: Check this function
 		txt := sb.String()
-		if sym == SymFloat {
+		switch symbol {
+		case sym.SymFloat:
 			value, err = strconv.ParseFloat(txt, 64)
-		} else if sym == SymFraction {
+		case sym.SymFraction:
 			// value, err = kern.MakeGeneratingFraction(txt)
 			value = txt
-		} else {
+		default:
 			value, err = strconv.ParseInt(txt, numBase, 64)
 		}
-		tk = scanner.MakeValueToken(sym, txt, value)
+		tk = scanner.MakeValueToken(symbol, txt, value)
 		// if err == nil {
 		// 	tk = scanner.MakeValueToken(sym, txt, value)
 		// } else {
@@ -546,17 +573,17 @@ func (scanner *Scanner) fetchIdentifier(firstCh byte) (tk *Token) {
 	} else {
 		txt := sb.String()
 		uptxt := strings.ToUpper(txt)
-		if sym, ok := keywords[uptxt]; ok {
-			tk = scanner.makeKeywordToken(sym, uptxt)
+		if symbol, ok := sym.Keywords[uptxt]; ok {
+			tk = scanner.makeKeywordToken(symbol, uptxt)
 		} else if uptxt == `TRUE` {
-			tk = scanner.MakeValueToken(SymBool, txt, true)
+			tk = scanner.MakeValueToken(sym.SymBool, txt, true)
 		} else if uptxt == `FALSE` {
-			tk = scanner.MakeValueToken(SymBool, txt, false)
+			tk = scanner.MakeValueToken(sym.SymBool, txt, false)
 		} else if ch, _ := scanner.peek(); ch == '(' {
 			scanner.readChar()
-			tk = scanner.MakeValueToken(SymFuncCall, txt+"(", txt)
+			tk = scanner.MakeValueToken(sym.SymFuncCall, txt+"(", txt)
 		} else {
-			tk = scanner.MakeValueToken(SymIdentifier, txt, txt)
+			tk = scanner.MakeValueToken(sym.SymIdentifier, txt, txt)
 		}
 	}
 
@@ -577,14 +604,14 @@ func (scanner *Scanner) fetchIdentifier(firstCh byte) (tk *Token) {
 }
 
 func (scanner *Scanner) fetchBlockComment() *Token {
-	return scanner.fetchUntil(SymComment, false, '*', '/')
+	return scanner.fetchUntil(sym.SymComment, false, '*', '/')
 }
 
 func (scanner *Scanner) fetchOnLineComment() *Token {
-	return scanner.fetchUntil(SymComment, true, '\n')
+	return scanner.fetchUntil(sym.SymComment, true, '\n')
 }
 
-func (scanner *Scanner) fetchUntil(sym Symbol, allowEos bool, endings ...byte) (tk *Token) {
+func (scanner *Scanner) fetchUntil(sym sym.Symbol, allowEos bool, endings ...byte) (tk *Token) {
 	var err error
 	var ch byte
 	var sb strings.Builder
@@ -653,9 +680,9 @@ func (scanner *Scanner) fetchString(termCh byte, addQuote bool) (tk *Token) {
 	} else {
 		txt := sb.String()
 		if addQuote {
-			tk = scanner.MakeValueToken(SymString, `"`+txt+`"`, txt)
+			tk = scanner.MakeValueToken(sym.SymString, `"`+txt+`"`, txt)
 		} else {
-			tk = scanner.MakeValueToken(SymString, txt, txt)
+			tk = scanner.MakeValueToken(sym.SymString, txt, txt)
 		}
 	}
 	return
@@ -677,7 +704,7 @@ func (scanner *Scanner) skipBlanks() (err error) {
 	return
 }
 
-func (scanner *Scanner) translate(sym Symbol) Symbol {
+func (scanner *Scanner) translate(sym sym.Symbol) sym.Symbol {
 	if scanner.translations != nil {
 		if translatedSym, ok := scanner.translations[sym]; ok {
 			return translatedSym
@@ -686,7 +713,7 @@ func (scanner *Scanner) translate(sym Symbol) Symbol {
 	return sym
 }
 
-func (scanner *Scanner) moveOn(sym Symbol, chars ...byte) (tk *Token) {
+func (scanner *Scanner) moveOn(sym sym.Symbol, chars ...byte) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), string(chars))
 	// for i := 1; i < len(chars); i++ {
 	if len(chars) > 1 {
@@ -696,22 +723,22 @@ func (scanner *Scanner) moveOn(sym Symbol, chars ...byte) (tk *Token) {
 	return
 }
 
-func (scanner *Scanner) accept(sym Symbol, chars ...byte) (tk *Token) {
+func (scanner *Scanner) accept(sym sym.Symbol, chars ...byte) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), string(chars))
 	return
 }
 
-func (scanner *Scanner) MakeToken(sym Symbol, chars ...byte) (tk *Token) {
+func (scanner *Scanner) MakeToken(sym sym.Symbol, chars ...byte) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), string(chars))
 	return
 }
 
-func (scanner *Scanner) makeKeywordToken(sym Symbol, upperCaseKeyword string) (tk *Token) {
+func (scanner *Scanner) makeKeywordToken(sym sym.Symbol, upperCaseKeyword string) (tk *Token) {
 	tk = NewToken(scanner.row, scanner.column, scanner.translate(sym), upperCaseKeyword)
 	return
 }
 
-func (scanner *Scanner) MakeValueToken(sym Symbol, source string, value any) (tk *Token) {
+func (scanner *Scanner) MakeValueToken(sym sym.Symbol, source string, value any) (tk *Token) {
 	tk = NewValueToken(scanner.row, scanner.column, scanner.translate(sym), source, value)
 	return
 }