55 lines
1.2 KiB
Go
55 lines
1.2 KiB
Go
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package lang
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import "fmt"
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// Match is used to pattern match an arbitrary Term against a pattern. A pattern
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// is a 2-tuple of the type (as an atom, e.g. AAtom, AConst) and a matching
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// value.
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//
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// If the value is AUnder the pattern will match all Terms of the type,
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// regardless of their value. If the pattern's type and value are both AUnder
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// the pattern will match all Terms.
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//
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// If the pattern's value is a Tuple or a List, each of its values will be used
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// as a sub-pattern to match against the corresponding value in the value.
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func Match(pat Tuple, t Term) bool {
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if len(pat) != 2 {
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return false
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}
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pt, pv := pat[0], pat[1]
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switch pt {
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case AAtom:
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a, ok := t.(Atom)
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return ok && (Equal(pv, AUnder) || Equal(pv, a))
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case AConst:
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c, ok := t.(Const)
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return ok && (Equal(pv, AUnder) || Equal(pv, c))
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case ATuple:
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tt, ok := t.(Tuple)
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if !ok {
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return false
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} else if Equal(pv, AUnder) {
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return true
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}
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pvt := pv.(Tuple)
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if len(tt) != len(pvt) {
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return false
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}
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for i := range tt {
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pvti, ok := pvt[i].(Tuple)
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if !ok || !Match(pvti, tt[i]) {
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return false
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}
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}
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return true
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case AList:
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panic("TODO")
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case AUnder:
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return true
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default:
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panic(fmt.Sprintf("unknown type %T", pt))
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}
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}
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