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parser.go
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parser.go
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package parser
import (
"fmt"
"github.com/ChrisTrenkamp/goxpath/lexer"
)
type stateType int
const (
defState stateType = iota
xpathState
funcState
paramState
predState
parenState
)
type parseStack struct {
stack []*Node
stateTypes []stateType
cur *Node
}
func (p *parseStack) push(t stateType) {
p.stack = append(p.stack, p.cur)
p.stateTypes = append(p.stateTypes, t)
}
func (p *parseStack) pop() {
stackPos := len(p.stack) - 1
p.cur = p.stack[stackPos]
p.stack = p.stack[:stackPos]
p.stateTypes = p.stateTypes[:stackPos]
}
func (p *parseStack) curState() stateType {
if len(p.stateTypes) == 0 {
return defState
}
return p.stateTypes[len(p.stateTypes)-1]
}
type lexFn func(*parseStack, lexer.XItem)
var parseMap = map[lexer.XItemType]lexFn{
lexer.XItemAbsLocPath: xiXPath,
lexer.XItemAbbrAbsLocPath: xiXPath,
lexer.XItemAbbrRelLocPath: xiXPath,
lexer.XItemRelLocPath: xiXPath,
lexer.XItemEndPath: xiEndPath,
lexer.XItemAxis: xiXPath,
lexer.XItemAbbrAxis: xiXPath,
lexer.XItemNCName: xiXPath,
lexer.XItemQName: xiXPath,
lexer.XItemNodeType: xiXPath,
lexer.XItemProcLit: xiXPath,
lexer.XItemFunction: xiFunc,
lexer.XItemArgument: xiFuncArg,
lexer.XItemEndFunction: xiEndFunc,
lexer.XItemPredicate: xiPred,
lexer.XItemEndPredicate: xiEndPred,
lexer.XItemStrLit: xiValue,
lexer.XItemNumLit: xiValue,
lexer.XItemOperator: xiOp,
lexer.XItemVariable: xiValue,
}
var opPrecedence = map[string]int{
"|": 1,
"*": 2,
"div": 2,
"mod": 2,
"+": 3,
"-": 3,
"=": 4,
"!=": 4,
"<": 4,
"<=": 4,
">": 4,
">=": 4,
"and": 5,
"or": 6,
}
//Parse creates an AST tree for XPath expressions.
func Parse(xp string) (*Node, error) {
var err error
c := lexer.Lex(xp)
n := &Node{}
p := &parseStack{cur: n}
for next := range c {
if next.Typ != lexer.XItemError {
parseMap[next.Typ](p, next)
} else if err == nil {
err = fmt.Errorf(next.Val)
}
}
return n, err
}
func xiXPath(p *parseStack, i lexer.XItem) {
if p.curState() == xpathState {
p.cur.push(i)
p.cur = p.cur.next
return
}
if p.cur.Val.Typ == lexer.XItemFunction {
p.cur.Right = &Node{Val: i, Parent: p.cur}
p.cur.next = p.cur.Right
p.push(xpathState)
p.cur = p.cur.next
return
}
p.cur.pushNotEmpty(i)
p.push(xpathState)
p.cur = p.cur.next
}
func xiEndPath(p *parseStack, i lexer.XItem) {
p.pop()
}
func xiFunc(p *parseStack, i lexer.XItem) {
if p.cur.Val.Typ == Empty {
p.cur.pushNotEmpty(i)
p.push(funcState)
p.cur = p.cur.next
return
}
p.cur.push(i)
p.cur = p.cur.next
p.push(funcState)
}
func xiFuncArg(p *parseStack, i lexer.XItem) {
if p.curState() != funcState {
p.pop()
}
p.cur.push(i)
p.cur = p.cur.next
p.push(paramState)
p.cur.push(lexer.XItem{Typ: Empty, Val: ""})
p.cur = p.cur.next
}
func xiEndFunc(p *parseStack, i lexer.XItem) {
if p.curState() == paramState {
p.pop()
}
p.pop()
}
func xiPred(p *parseStack, i lexer.XItem) {
p.cur.push(i)
p.cur = p.cur.next
p.push(predState)
p.cur.push(lexer.XItem{Typ: Empty, Val: ""})
p.cur = p.cur.next
}
func xiEndPred(p *parseStack, i lexer.XItem) {
p.pop()
}
func xiValue(p *parseStack, i lexer.XItem) {
p.cur.add(i)
}
func xiOp(p *parseStack, i lexer.XItem) {
if i.Val == "(" {
p.cur.push(lexer.XItem{Typ: Empty, Val: ""})
p.push(parenState)
p.cur = p.cur.next
return
}
if i.Val == ")" {
p.pop()
return
}
if p.cur.Val.Typ == lexer.XItemOperator {
if opPrecedence[p.cur.Val.Val] <= opPrecedence[i.Val] {
p.cur.add(i)
} else {
p.cur.push(i)
}
} else {
p.cur.add(i)
}
p.cur = p.cur.next
}