59 lines
1 KiB
Go
59 lines
1 KiB
Go
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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// Perform some post-construction validation. This currently does:
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//
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// Checks for left recursion.
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func validate(n node) error {
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checked := map[*strct]bool{}
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seen := map[node]bool{}
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return visit(n, func(n node, next func() error) error {
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if n, ok := n.(*strct); ok {
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if !checked[n] && isLeftRecursive(n) {
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return fmt.Errorf("left recursion detected on\n\n%s", indent(n.String()))
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}
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checked[n] = true
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if seen[n] {
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return nil
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}
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}
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seen[n] = true
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return next()
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})
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}
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func isLeftRecursive(root *strct) (found bool) {
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defer func() { _ = recover() }()
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seen := map[node]bool{}
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_ = visit(root.expr, func(n node, next func() error) error {
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if found {
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return nil
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}
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switch n := n.(type) {
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case *strct:
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if root.typ == n.typ {
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found = true
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}
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case *sequence:
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if !n.head {
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panic("done")
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}
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}
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if seen[n] {
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return nil
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}
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seen[n] = true
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return next()
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})
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return
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}
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func indent(s string) string {
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return " " + strings.Join(strings.Split(s, "\n"), "\n ")
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}
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