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|
package main
import (
"fmt"
"main/subex"
"strings"
"unicode/utf8"
)
type parser struct {
tokenStream chan Token
rewinds []Token
labels map[rune]int
}
func (p *parser) next() Token {
var token Token
if len(p.rewinds) == 0 {
token = <- p.tokenStream
} else {
token = p.rewinds[len(p.rewinds)-1]
p.rewinds = p.rewinds[:len(p.rewinds)-1]
}
if token.typ == TokenErr {
fmt.Println(token)
panic("Lexing error")
}
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
}
func (p *parser) parseSubex() subex.SubexAST {
delim := p.next()
if delim.typ != TokenSubstituteDelimiter {
panic("Missing substitute delimiter")
}
subexProgramToken := p.next()
if subexProgramToken.typ != TokenSubex {
panic("Missing subex from substitution")
}
var subexProgram string
if delim.val == "=" || delim.val == "~" || delim.val == "\"" || delim.val == "`" || delim.val == "^" {
subexProgram = delim.val + subexProgramToken.val + delim.val
} else {
subexProgram = subexProgramToken.val
}
reader := subex.NewStringRuneReader(subexProgram)
subexAST := subex.Parse(reader)
delim = p.next()
if delim.typ != TokenSubstituteDelimiter {
panic("Missing end substitute delimiter")
}
return subexAST
}
func (p *parser) parseBasicCommand(commands []Command, commandChar rune) []Command {
switch commandChar {
case 'p':
return append(commands, PrintValueCommand{})
case 'd':
return append(commands, DeleteValueCommand{})
case 'n':
return append(commands, NextCommand{})
case 'N':
return append(commands, AppendNextCommand{})
case 's':
ast := p.parseSubex()
subex := subex.CompileTransducer(ast)
return append(commands, SubstituteValueCommand {subex}, JumpCommand {len(commands) + 3})
case 'o':
return append(commands, NoopCommand{})
case 'x':
delim := p.peek()
if delim.typ != TokenSubstituteDelimiter {
return append(commands, SwapXRegCommand{})
}
ast := p.parseSubex()
subex := subex.CompileTransducer(ast)
return append(commands, SubstituteToXRegCommand {subex}, JumpCommand {len(commands) + 3})
case 'X':
delim := p.peek()
if delim.typ != TokenSubstituteDelimiter {
return append(commands, AppendXRegCommand{})
}
ast := p.parseSubex()
subex := subex.CompileTransducer(ast)
return append(commands, SubstituteAppendXRegCommand {subex}, JumpCommand {len(commands) + 3})
case 'y':
delim := p.peek()
if delim.typ != TokenSubstituteDelimiter {
return append(commands, SwapYRegCommand{})
}
ast := p.parseSubex()
subex := subex.CompileTransducer(ast)
return append(commands, SubstituteToYRegCommand {subex}, JumpCommand {len(commands) + 3})
case 'Y':
delim := p.peek()
if delim.typ != TokenSubstituteDelimiter {
return append(commands, AppendYRegCommand{})
}
ast := p.parseSubex()
subex := subex.CompileTransducer(ast)
return append(commands, SubstituteAppendYRegCommand {subex}, JumpCommand {len(commands) + 3})
case 'z':
delim := p.peek()
if delim.typ != TokenSubstituteDelimiter {
return append(commands, SwapZRegCommand{})
}
ast := p.parseSubex()
subex := subex.CompileTransducer(ast)
return append(commands, SubstituteToZRegCommand {subex}, JumpCommand {len(commands) + 3})
case 'Z':
delim := p.peek()
if delim.typ != TokenSubstituteDelimiter {
return append(commands, AppendZRegCommand{})
}
ast := p.parseSubex()
subex := subex.CompileTransducer(ast)
return append(commands, SubstituteAppendZRegCommand {subex}, JumpCommand {len(commands) + 3})
case 'a':
return append(commands, IsStartCommand{}, JumpCommand {len(commands) + 3})
case 'A':
return append(commands, IsPrevStartCommand{}, JumpCommand {len(commands) + 3})
case 'e':
return append(commands, IsEndCommand{}, JumpCommand {len(commands) + 3})
case 'E':
return append(commands, IsNextEndCommand{}, JumpCommand {len(commands) + 3})
case ':':
labelToken := p.next()
if labelToken.typ != TokenLabel {
panic("Missing branch label")
}
label, _ := utf8.DecodeRuneInString(labelToken.val)
p.labels[label] = len(commands)
return commands
case 'b':
labelToken := p.next()
if labelToken.typ != TokenLabel {
panic("Missing branch label")
}
label, _ := utf8.DecodeRuneInString(labelToken.val)
return append(commands, BranchPlaceholderCommand {label})
default:
panic("Invalid command")
}
}
func (p *parser) parseCommand(commands []Command) []Command {
token := p.next()
switch token.typ {
case TokenLBrace:
jumpToBlockCommand := &JumpCommand{0}
commands = append(commands, JumpCommand {len(commands) + 2}, jumpToBlockCommand)
commands = p.parseCommands(commands)
if p.next().typ != TokenRBrace {
panic("Missing matching }")
}
jumpToBlockCommand.destination = len(commands)
return commands
case TokenCommand:
commandChar, _, err := strings.NewReader(token.val).ReadRune()
if err != nil {
panic("Error reading a command character!?")
}
return p.parseBasicCommand(commands, commandChar)
default:
panic("Invalid token, expected command")
}
}
func (p *parser) parseCommands(commands []Command) []Command {
for {
nextToken := p.peek()
if nextToken.typ == TokenEOF || nextToken.typ == TokenRBrace {
return commands
}
commands = p.parseCommand(commands)
}
}
func Parse(tokens chan Token) []Command {
p := parser {
tokenStream: tokens,
rewinds: nil,
labels: make(map[rune]int),
}
program := p.parseCommands(nil)
for i, command := range program {
switch branch := command.(type) {
case BranchPlaceholderCommand:
destination, exists := p.labels[branch.label]
if !exists {
panic("Tried to branch to a label that doesn't exist")
}
program[i] = JumpCommand {destination}
}
}
return program
}
|
