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package participle
import (
"fmt"
"strings"
)
// String returns the EBNF for the grammar.
//
// Productions are always upper case. Lexer tokens are always lower case.
func (p *Parser) String() string {
seen := map[node]bool{}
outp := []*ebnfp{}
ebnf(p.root, seen, nil, &outp)
out := []string{}
for _, p := range outp {
out = append(out, fmt.Sprintf("%s = %s .", p.name, p.out))
}
return strings.Join(out, "\n")
}
type ebnfp struct {
name string
out string
}
func ebnf(n node, seen map[node]bool, p *ebnfp, outp *[]*ebnfp) {
switch n := n.(type) {
case *disjunction:
for i, next := range n.nodes {
if i > 0 {
p.out += " | "
}
ebnf(next, seen, p, outp)
}
return
case *strct:
name := strings.ToUpper(n.typ.Name()[:1]) + n.typ.Name()[1:]
if p != nil {
p.out += name
}
if seen[n] {
return
}
seen[n] = true
p = &ebnfp{name: name}
*outp = append(*outp, p)
ebnf(n.expr, seen, p, outp)
return
case *sequence:
ebnf(n.node, seen, p, outp)
if n.next != nil {
p.out += " "
ebnf(n.next, seen, p, outp)
}
return
case *parseable:
p.out += n.t.Name()
case *capture:
ebnf(n.node, seen, p, outp)
case *reference:
p.out += strings.ToLower(n.identifier)
case *optional:
ebnf(n.node, seen, p, outp)
p.out += "?"
case *repetition:
ebnf(n.node, seen, p, outp)
p.out += "*"
case *negation:
p.out += "!"
ebnf(n.node, seen, p, outp)
return
case *literal:
p.out += fmt.Sprintf("%q", n.s)
case *group:
composite := (n.mode != groupMatchOnce) && compositeNode(map[node]bool{}, n, false)
if composite {
p.out += "("
}
if child, ok := n.expr.(*group); ok && child.mode == groupMatchOnce {
ebnf(child.expr, seen, p, outp)
} else if child, ok := n.expr.(*capture); ok {
if grandchild, ok := child.node.(*group); ok && grandchild.mode == groupMatchOnce {
ebnf(grandchild.expr, seen, p, outp)
} else {
ebnf(n.expr, seen, p, outp)
}
} else {
ebnf(n.expr, seen, p, outp)
}
if composite {
p.out += ")"
}
switch n.mode {
case groupMatchNonEmpty:
p.out += "!"
case groupMatchZeroOrOne:
p.out += "?"
case groupMatchZeroOrMore:
p.out += "*"
case groupMatchOneOrMore:
p.out += "+"
}
return
default:
panic(fmt.Sprintf("unsupported node type %T", n))
}
}
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