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|
package subex
import (
"main/walk"
)
func expectBracket(l *RuneReader, ifLeft walk.Atom, ifRight walk.Atom) walk.Atom {
switch l.next() {
case '(':
return ifLeft
case ')':
return ifRight
default:
panic("Expected ( or )")
}
}
// Having just read termType, read in a bracket and return the corresponding Atom
func parseTerminatorAtomLiteral(termType rune, l *RuneReader) walk.Atom {
switch termType {
case '@':
return expectBracket(l, walk.ArrayBegin, walk.ArrayEnd)
case '~':
return expectBracket(l, walk.StartString{}, walk.EndString{})
case '#':
return expectBracket(l, walk.MapBegin, walk.MapEnd)
default:
return nil
}
}
func parseReplacement(l *RuneReader) (output []TransducerOutput) {
// TODO escaping
loop: for {
r := l.next()
switch r {
case eof:
panic("Missing closing \"")
case '"':
break loop
case '$':
slot := l.next()
if slot == eof {
panic("Missing slot character")
}
output = append(output, TransducerReplacementLoad{slot: slot})
case '@', '~', '#':
output = append(output, TransducerReplacementAtom{atom: parseTerminatorAtomLiteral(r, l)})
default:
output = append(output, TransducerReplacementAtom{atom: r})
}
}
return output
}
// Parse the contents of a range subex [] into a map
func parseRangeSubex(l *RuneReader) map[walk.Atom]walk.Atom {
// TODO escaping
parts := make(map[walk.Atom]walk.Atom)
var froms []walk.Atom
var hasTo bool
for {
fromsStart := l.next()
if fromsStart == ']' {
hasTo = false
break
} else if fromsStart == '=' {
hasTo = true
break
} else {
atom := parseTerminatorAtomLiteral(fromsStart, l)
if atom != nil {
froms = append(froms, atom)
continue
}
}
if l.accept("-") {
fromsEnd := l.next()
if fromsEnd == ']' || fromsEnd == '=' {
l.rewind()
fromsEnd = fromsStart
}
for i := fromsStart; i <= fromsEnd; i += 1 {
froms = append(froms, i)
}
} else {
froms = append(froms, fromsStart)
}
}
if len(froms) == 0 {
panic("Missing from part of range expression")
}
var tos []walk.Atom
if hasTo {
for {
tosStart := l.next()
if tosStart == ']' {
break
} else {
atom := parseTerminatorAtomLiteral(tosStart, l)
if atom != nil {
tos = append(tos, atom)
continue
}
}
if l.accept("-") {
tosEnd := l.next()
if tosEnd == ']' {
l.rewind()
tosEnd = tosStart
}
for i := tosStart; i <= tosEnd; i += 1 {
tos = append(tos, i)
}
} else {
tos = append(tos, tosStart)
}
}
} else {
tos = froms
}
if len(tos) == 0 {
panic("Missing to part of range expression")
}
for i, from := range froms {
parts[from] = tos[i % len(tos)]
}
return parts
}
func parseSubex(l *RuneReader, minPower int) SubexAST {
var lhs SubexAST
r := l.next()
switch r {
case eof:
return nil
case '(':
lhs = parseSubex(l, 0)
if !l.accept(")") {
panic("Missing matching )")
}
case '[':
rangeParts := parseRangeSubex(l)
lhs = SubexASTRange {rangeParts}
case ')', '*', '-', '|', '!', '?', ';':
l.rewind()
return nil
case '$':
slot := l.next()
if slot == eof {
panic("Missing slot character")
}
match := parseSubex(l, 100)
if match == nil {
panic("Missing regex for store")
}
lhs = SubexASTStore{
match: match,
slot: slot,
}
case '"':
replacement := parseReplacement(l)
lhs = SubexASTOutput{replacement}
case '.':
lhs = SubexASTCopyAny{}
case '@', '#', '~':
lhs = SubexASTCopyAtom{atom: parseTerminatorAtomLiteral(r, l)}
default:
lhs = SubexASTCopyAtom{atom: r}
}
loop: for {
if minPower <= 0 {
next := parseSubex(l, 1)
if next != nil {
lhs = SubexASTConcat{lhs, next}
continue loop
}
}
r := l.next()
switch {
case r == '*' && minPower <= 8:
lhs = SubexASTMaximise{lhs}
case r == '-' && minPower <= 8:
lhs = SubexASTMinimise{lhs}
case r == '!' && minPower <= 8:
lhs = SubexASTTry{lhs}
case r == '?' && minPower <= 8:
lhs = SubexASTMaybe{lhs}
case r == '|' && minPower <= 4:
rhs := parseSubex(l, 5)
if rhs == nil {
panic("Missing subex after |")
}
lhs = SubexASTOr{lhs, rhs}
case r == ';' && minPower <= 2:
rhs := parseSubex(l, 3)
if rhs == nil {
panic("Missing subex after ;")
}
lhs = SubexASTJoin{
content: lhs,
delimiter: rhs,
}
default:
l.rewind()
break loop
}
}
return lhs
}
func Parse(input string) SubexAST {
l := RuneReader {
input: input,
pos: 0,
width: 0,
}
return parseSubex(&l, 0)
}
|
