parser: add support for unary operators

1 files changed, 13 insertions, 2 deletions

diff --git a/parser/expr.go b/parser/expr.go
index fa8afa4..207f38b 100644
--- a/parser/expr.go
+++ b/parser/expr.go
@@ -42,10 +42,21 @@ func (p *Parser) ParseExpr(in Tokens) (out Tokens, err error) {
 		case lang.Int, lang.String:
 			out = append(out, t)
 			vl++
-		case lang.Define, lang.Add, lang.Sub, lang.Assign, lang.Equal, lang.Greater, lang.Less, lang.Mul, lang.Land, lang.Lor, lang.Shl, lang.Shr:
+		case lang.Define, lang.Add, lang.Sub, lang.Assign, lang.Equal, lang.Greater, lang.Less, lang.Mul, lang.Land, lang.Lor, lang.Shl, lang.Shr, lang.Not:
+			if i == 0 || in[i-1].Id.IsOperator() {
+				// An operator preceded by an operator or no token is unary.
+				t.Id = lang.UnaryOp[t.Id]
+				j := len(out) - 1
+				l := out[j]
+				if p.precedence(l) > 0 {
+					out = append(out[:j], t, l)
+					break
+				}
+				out = append(out, t)
+				break
+			}
 			if vl < 2 {
 				ops = append(ops, t)
-				break
 			}
 		case lang.ParenBlock:
 			// If the previous token is an arithmetic, logic or assign operator then