From 9fa07b376dd52ee8bbcc074e59d36af3f3f2536d Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <e.dolstra@tudelft.nl>
Date: Tue, 26 Oct 2004 17:01:35 +0000
Subject: * String/path concatenation operator (`+').

---
 src/libexpr/eval.cc | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

(limited to 'src/libexpr/eval.cc')

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 215692aeb313..4454aaec452f 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -338,6 +338,20 @@ Expr evalExpr2(EvalState & state, Expr e)
         return makeBool(attrs.get(name) != 0);
     }
 
+    /* String or path concatenation. */
+    if (atMatch(m, e) >> "OpPlus" >> e1 >> e2) {
+        e1 = evalExpr(state, e1);
+        e2 = evalExpr(state, e2);
+        string s1, s2;
+        if (atMatch(m, e1) >> "Str" >> s1 &&
+            atMatch(m, e2) >> "Str" >> s2)
+            return makeString(s1 + s2);
+        else if (atMatch(m, e1) >> "Path" >> s1 &&
+            atMatch(m, e2) >> "Path" >> s2)
+            return makeString(canonPath(s1 + "/" + s2));
+        else throw Error("wrong argument types in `+' operator");
+    }
+
     /* Barf. */
     throw badTerm("invalid expression", e);
 }
-- 
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