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authorShea Levy <shea@shealevy.com>2014-10-16T02·04-0400
committerShea Levy <shea@shealevy.com>2014-11-15T21·12-0500
commit997defa16617caf5fd869924558389639d1c8caf (patch)
treeba286d246324da0066c8528639e43bd26c986cdb /src/libexpr/eval.cc
parent8cfe939b0f222e3b27493a3c62e0b1088b12e110 (diff)
Add functors (callable attribute sets).
With this, attribute sets with a `__functor` attribute can be applied
just like normal functions. This can be used to attach arbitrary
metadata to a function without callers needing to treat it specially.
Diffstat (limited to 'src/libexpr/eval.cc')
-rw-r--r--src/libexpr/eval.cc12
1 files changed, 12 insertions, 0 deletions
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 8bc992d0350b..81774974a90c 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -180,6 +180,7 @@ EvalState::EvalState(const Strings & _searchPath)
     , sFile(symbols.create("file"))
     , sLine(symbols.create("line"))
     , sColumn(symbols.create("column"))
+    , sFunctor(symbols.create("__functor"))
     , repair(false)
     , baseEnv(allocEnv(128))
     , staticBaseEnv(false, 0)
@@ -885,6 +886,17 @@ void EvalState::callFunction(Value & fun, Value & arg, Value & v, const Pos & po
         return;
     }
 
+    if (fun.type == tAttrs) {
+      auto found = fun.attrs->find(sFunctor);
+      if (found != fun.attrs->end()) {
+        forceValue(*found->value);
+        Value * v2 = allocValue();
+        callFunction(*found->value, fun, *v2, pos);
+        forceValue(*v2);
+        return callFunction(*v2, arg, v, pos);
+      }
+    }
+
     if (fun.type != tLambda)
         throwTypeError("attempt to call something which is not a function but %1%, at %2%", fun, pos);