Add substitute next commands

1 files changed, 9 insertions, 1 deletions

diff --git a/subex/parse.go b/subex/parse.go
index d825f75..b6bf2f6 100644
--- a/subex/parse.go
+++ b/subex/parse.go
@@ -516,7 +516,14 @@ func parseSubex(l RuneReader, minPower int, inType Type) (lhs SubexAST, outType
 			lhs = SubexASTCopyNumber{}
 		case '`':
 			outType = inType
-			lhs = parseValueReplacement(l, '`')
+			switch inType {
+			case ValueType:
+				lhs = parseValueReplacement(l, '`')
+			case RuneType:
+				lhs = parseRuneReplacement(l, '`')
+			default:
+				panic("Invalid inType")
+			}
 		case ' ':
 			if inType == RuneType {
 				outType = RuneType
@@ -540,6 +547,7 @@ func parseSubex(l RuneReader, minPower int, inType Type) (lhs SubexAST, outType
 	loop: for {
 		if minPower <= 20 {
 			next, outType2 := parseSubex(l, 21, inType)
+			// TODO: next might legitimately be SubexASTEmpty, e.g. ``
 			if next != nil && (next != SubexASTEmpty{}) {
 				outType = resolveTypes(outType, outType2)
 				lhs = SubexASTConcat{lhs, next}