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