super-graph/qcode/lex.go
Vikram Rangnekar b9d38a5e9d First commit
2019-03-24 09:57:29 -04:00

392 lines
7.8 KiB
Go

package qcode
import (
"fmt"
"strings"
"unicode"
"unicode/utf8"
)
// Pos represents a byte position in the original input text from which
// this template was parsed.
type Pos int
func (p Pos) Position() Pos {
return p
}
// item represents a token or text string returned from the scanner.
type item struct {
typ itemType // The type of this item.
pos Pos // The starting position, in bytes, of this item in the input string.
val string // The value of this item.
line int // The line number at the start of this item.
}
func (i *item) String() string {
var v string
switch i.typ {
case itemEOF:
v = "EOF"
case itemError:
v = "error"
case itemName:
v = "name"
case itemQuery:
v = "query"
case itemMutation:
v = "mutation"
case itemSub:
v = "subscription"
case itemPunctuator:
v = "punctuator"
case itemDirective:
v = "directive"
case itemVariable:
v = "variable"
case itemIntVal:
v = "int"
case itemFloatVal:
v = "float"
case itemStringVal:
v = "string"
}
return fmt.Sprintf("%s %q", v, i.val)
}
// itemType identifies the type of lex items.
type itemType int
const (
itemError itemType = iota // error occurred; value is text of error
itemEOF
itemName
itemQuery
itemMutation
itemSub
itemPunctuator
itemArgsOpen
itemArgsClose
itemListOpen
itemListClose
itemObjOpen
itemObjClose
itemColon
itemEquals
itemDirective
itemVariable
itemSpread
itemIntVal
itemFloatVal
itemStringVal
itemBoolVal
)
// !$():=@[]{|}
var punctuators = map[rune]itemType{
'{': itemObjOpen,
'}': itemObjClose,
'[': itemListOpen,
']': itemListClose,
'(': itemArgsOpen,
')': itemArgsClose,
':': itemColon,
'=': itemEquals,
}
const eof = -1
// stateFn represents the state of the scanner as a function that returns the next state.
type stateFn func(*lexer) stateFn
// lexer holds the state of the scanner.
type lexer struct {
name string // the name of the input; used only for error reports
input string // the string being scanned
pos Pos // current position in the input
start Pos // start position of this item
width Pos // width of last rune read from input
items []item // array of scanned items
line int // 1+number of newlines seen
}
// next returns the next rune in the input.
func (l *lexer) next() rune {
if int(l.pos) >= len(l.input) {
l.width = 0
return eof
}
r, w := utf8.DecodeRuneInString(l.input[l.pos:])
l.width = Pos(w)
l.pos += l.width
if r == '\n' {
l.line++
}
return r
}
// peek returns but does not consume the next rune in the input.
func (l *lexer) peek() rune {
r := l.next()
l.backup()
return r
}
// backup steps back one rune. Can only be called once per call of next.
func (l *lexer) backup() {
l.pos -= l.width
// Correct newline count.
if l.width == 1 && l.input[l.pos] == '\n' {
l.line--
}
}
func (l *lexer) current() string {
return l.input[l.start:l.pos]
}
// emit passes an item back to the client.
func (l *lexer) emit(t itemType) {
l.items = append(l.items, item{t, l.start, l.input[l.start:l.pos], l.line})
// Some items contain text internally. If so, count their newlines.
switch t {
case itemName:
l.line += strings.Count(l.input[l.start:l.pos], "\n")
}
l.start = l.pos
}
// ignore skips over the pending input before this point.
func (l *lexer) ignore() {
l.line += strings.Count(l.input[l.start:l.pos], "\n")
l.start = l.pos
}
// accept consumes the next rune if it's from the valid set.
func (l *lexer) accept(valid string) bool {
if strings.ContainsRune(valid, l.next()) {
return true
}
l.backup()
return false
}
// accept onsumes a run of runes while they are alpha nums
func (l *lexer) acceptAlphaNum() bool {
n := 0
for r := l.next(); isAlphaNumeric(r); r = l.next() {
n++
}
l.backup()
return (n != 0)
}
// acceptRun consumes a run of runes from the valid set.
func (l *lexer) acceptRun(valid string) {
for strings.ContainsRune(valid, l.next()) {
}
l.backup()
}
// errorf returns an error token and terminates the scan by passing
// back a nil pointer that will be the next state, terminating l.nextItem.
func (l *lexer) errorf(format string, args ...interface{}) stateFn {
l.items = append(l.items, item{itemError, l.start,
fmt.Sprintf(format, args...), l.line})
return nil
}
// lex creates a new scanner for the input string.
func lex(input string) (*lexer, error) {
l := &lexer{
input: input,
items: make([]item, 0, 100),
line: 1,
}
l.run()
if last := l.items[len(l.items)-1]; last.typ == itemError {
return nil, fmt.Errorf(last.val)
}
return l, nil
}
// run runs the state machine for the lexer.
func (l *lexer) run() {
for state := lexRoot; state != nil; {
state = state(l)
}
}
// lexInsideAction scans the elements inside action delimiters.
func lexRoot(l *lexer) stateFn {
r := l.next()
switch {
case r == eof:
l.emit(itemEOF)
return nil
case isEndOfLine(r):
l.ignore()
case isSpace(r):
l.ignore()
case r == '@':
l.ignore()
if l.acceptAlphaNum() {
l.emit(itemDirective)
}
case r == '$':
l.ignore()
if l.acceptAlphaNum() {
l.emit(itemVariable)
}
case strings.ContainsRune("!():=[]{|}", r):
if item, ok := punctuators[r]; ok {
l.emit(item)
} else {
l.emit(itemPunctuator)
}
case r == '"' || r == '\'':
l.backup()
return lexString
case r == '.':
if len(l.input) >= 3 {
if strings.HasSuffix(l.input[:l.pos], "...") {
l.emit(itemSpread)
return lexRoot
}
}
fallthrough // '.' can start a number.
case r == '+' || r == '-' || ('0' <= r && r <= '9'):
l.backup()
return lexNumber
case isAlphaNumeric(r):
l.backup()
return lexName
default:
return l.errorf("unrecognized character in action: %#U", r)
}
return lexRoot
}
// lexName scans a name.
func lexName(l *lexer) stateFn {
for {
r := l.next()
if r == eof {
l.emit(itemEOF)
return nil
}
if !isAlphaNumeric(r) {
l.backup()
v := l.current()
if len(v) == 0 {
switch {
case strings.EqualFold(v, "query"):
l.emit(itemQuery)
break
case strings.EqualFold(v, "mutation"):
l.emit(itemMutation)
break
case strings.EqualFold(v, "subscription"):
l.emit(itemSub)
break
}
}
switch {
case strings.EqualFold(v, "true"):
l.emit(itemBoolVal)
case strings.EqualFold(v, "false"):
l.emit(itemBoolVal)
default:
l.emit(itemName)
}
break
}
}
return lexRoot
}
// lexString scans a string.
func lexString(l *lexer) stateFn {
if l.accept("\"'") {
l.ignore()
for {
r := l.next()
if r == eof {
l.emit(itemEOF)
return nil
}
if r == '\'' || r == '"' {
l.backup()
l.emit(itemStringVal)
if l.accept("\"'") {
l.ignore()
}
break
}
}
}
return lexRoot
}
// lexNumber scans a number: decimal, octal, hex, float, or imaginary. This
// isn't a perfect number scanner - for instance it accepts "." and "0x0.2"
// and "089" - but when it's wrong the input is invalid and the parser (via
// strconv) will notice.
func lexNumber(l *lexer) stateFn {
var it itemType
// Optional leading sign.
l.accept("+-")
// Is it integer
digits := "0123456789"
if l.accept(digits) {
l.acceptRun(digits)
it = itemIntVal
}
// Is it float
if l.peek() == '.' {
if l.accept(".") {
if l.accept(digits) {
l.acceptRun(digits)
it = itemFloatVal
}
} else {
l.backup()
}
}
// Next thing mustn't be alphanumeric.
if isAlphaNumeric(l.peek()) {
l.next()
return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
}
if it != 0 {
l.emit(it)
}
return lexRoot
}
// isSpace reports whether r is a space character.
func isSpace(r rune) bool {
return r == ',' || r == ' ' || r == '\t'
}
// isEndOfLine reports whether r is an end-of-line character.
func isEndOfLine(r rune) bool {
return r == '\r' || r == '\n'
}
// isAlphaNumeric reports whether r is an alphabetic, digit, or underscore.
func isAlphaNumeric(r rune) bool {
return r == '_' || unicode.IsLetter(r) || unicode.IsDigit(r)
}