* Added a list concatenation operator:

    [1 2 3] ++ [4 5 6] => [1 2 3 4 5 6]

1 files changed, 16 insertions, 0 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index d4593b5c0e..9a6d414db7 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -140,6 +140,15 @@ bool evalBool(EvalState & state, Expr e)
 }
 
 
+ATermList evalList(EvalState & state, Expr e)
+{
+    e = evalExpr(state, e);
+    ATermList list;
+    if (!matchList(e, list)) throw Error("list expected");
+    return list;
+}
+
+
 Expr evalExpr2(EvalState & state, Expr e)
 {
     Expr e1, e2, e3, e4;
@@ -336,6 +345,13 @@ Expr evalExpr2(EvalState & state, Expr e)
         else throw Error("wrong argument types in `+' operator");
     }
 
+    /* List concatenation. */
+    if (matchOpConcat(e, e1, e2)) {
+        ATermList l1 = evalList(state, e1);
+        ATermList l2 = evalList(state, e2);
+        return makeList(ATconcat(l1, l2));
+    }
+
     /* Barf. */
     throw badTerm("invalid expression", e);
 }