/
parser.go
87 lines (74 loc) · 1.56 KB
/
parser.go
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package backtrackingparser
import (
"fmt"
"regexp"
"github.com/shivamMg/rd"
. "github.com/shivamMg/rd/examples/arithmetic/tokens"
)
const Grammar = `
Expr = Term "+" Expr | Term "-" Expr | Term
Term = Factor "*" Term | Factor "/" Term | Factor
Factor = "(" Expr ")" | "-" Factor | Number
`
var numberRegex = regexp.MustCompile(`^(\d*\.\d+|\d+)$`)
func Expr(b *rd.Builder) (ok bool) {
b.Enter("Expr")
defer b.Exit(&ok)
if Term(b) && b.Match(Plus) && Expr(b) {
return true
}
b.Backtrack()
if Term(b) && b.Match(Minus) && Expr(b) {
return true
}
b.Backtrack()
return Term(b)
}
func Term(b *rd.Builder) (ok bool) {
b.Enter("Term")
defer b.Exit(&ok)
if Factor(b) && b.Match(Star) && Term(b) {
return true
}
b.Backtrack()
if Factor(b) && b.Match(Slash) && Term(b) {
return true
}
b.Backtrack()
return Factor(b)
}
func Factor(b *rd.Builder) (ok bool) {
b.Enter("Factor")
defer b.Exit(&ok)
if b.Match(OpenParen) && Expr(b) && b.Match(CloseParen) {
return true
}
b.Backtrack()
if b.Match(Minus) && Factor(b) {
return true
}
b.Backtrack()
return Number(b)
}
func Number(b *rd.Builder) (ok bool) {
b.Enter("Number")
defer b.Exit(&ok)
token, ok := b.Next()
if !ok {
return false
}
if numberRegex.MatchString(fmt.Sprint(token)) {
b.Add(token)
return true
}
b.Backtrack()
return false
}
func Parse(tokens []rd.Token) (parseTree *rd.Tree, debugTree *rd.DebugTree, err error) {
b := rd.NewBuilder(tokens)
ok := Expr(b)
if ok && b.Err() == nil {
return b.ParseTree(), b.DebugTree(), nil
}
return nil, b.DebugTree(), b.Err()
}