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|
package main
import (
"strings"
"strconv"
"fmt"
)
type parser struct {
tokenStream chan Token
rewinds []Token
}
func (p *parser) next() Token {
if len(p.rewinds) == 0 {
return <- p.tokenStream
}
token := p.rewinds[len(p.rewinds)-1]
p.rewinds = p.rewinds[:len(p.rewinds)-1]
return token
}
func (p *parser) rewind(token Token) {
p.rewinds = append(p.rewinds, token)
}
func (p *parser) peek() Token {
token := p.next()
p.rewind(token)
return token
}
// TODO: make a pratt parser
func (p *parser) parsePathPatternFilter() PathFilterAST {
var segments []PathFilterAST
loop: for {
token := p.next()
switch token.typ {
case TokenHash:
stringIndex := p.next()
if stringIndex.typ != TokenPatternStringIndex {
panic("Expected string index after # in pattern")
}
segments = append(segments, StringSegmentPathFilterAST{stringIndex.val})
case TokenAt:
intIndex := p.next()
if intIndex.typ != TokenPatternIntegerIndex {
panic("Expected integer index after @ in pattern")
}
index, err := strconv.Atoi(intIndex.val)
if err != nil {
panic("Expected integer index after @ in pattern")
}
segments = append(segments, IntegerSegmentPathFilterAST{index})
case TokenDot:
segments = append(segments, AnySegmentPathFilterAST{})
case TokenAst:
if len(segments) == 0 {
panic("Invalid * in pattern, * must go after something")
}
segments[len(segments) - 1] = RepeatPathFilterAST {segments[len(segments)-1]}
default:
p.rewind(token)
break loop
}
}
return SequencePathFilterAST {segments}
}
// TODO: should only return a single filter
func (p *parser) parseFilter() []Filter {
var filters []Filter
token := p.next()
switch token.typ {
case TokenHash, TokenAt, TokenDot:
p.rewind(token)
filterAst := p.parsePathPatternFilter()
filters = append(filters, compilePathFilterAST(filterAst))
token = p.next()
}
if len(filters) == 0 {
panic("Missing filter")
}
p.rewind(token)
return filters
}
func (p *parser) parseBasicCommand(commandChar rune) Command {
switch commandChar {
case 'p':
return PrintValueCommand{}
case 'd':
return DeleteAllCommand{}
default:
panic("Invalid command")
}
}
func (p *parser) parseCommand() Command {
token := p.next()
switch token.typ {
case TokenHash, TokenAt, TokenDot:
p.rewind(token)
filters := p.parseFilter()
command := p.parseCommand()
for _, filter := range filters {
command = FilteredCommand {
filter: filter,
command: command,
}
}
return command
case TokenCommand:
commandChar, _, err := strings.NewReader(token.val).ReadRune()
if err != nil {
panic("Error reading a command character!?")
}
return p.parseBasicCommand(commandChar)
default:
fmt.Println(token)
panic("Invalid token, expected command")
}
}
func (p *parser) parseCommands() []Command {
var commands []Command
for {
nextToken := p.peek()
if nextToken.typ == TokenEOF || nextToken.typ == TokenRBrace {
return commands
}
commands = append(commands, p.parseCommand())
semicolon := p.next()
if semicolon.typ == TokenEOF || semicolon.typ == TokenRBrace {
return commands
}
if semicolon.typ != TokenSemicolon {
panic("Expected ; after command")
}
}
}
func Parse(tokens chan Token) []Command {
p := parser {
tokenStream: tokens,
}
return p.parseCommands()
}
|
