* Added an experimental feature suggested by Andres: ellipses ("...")

  in attribute set pattern matches.  This allows defining a function
  that takes *at least* the listed attributes, while ignoring
  additional attributes.  For instance,

    {stdenv, fetchurl, fuse, ...}:
    
    stdenv.mkDerivation {
      ...
    };
    
  defines a function that requires an attribute set that contains the 
  specified attributes but ignores others.  The main advantage is that
  we can then write in all-packages.nix

    aefs = import ../bla/aefs pkgs;

  instead of

    aefs = import ../bla/aefs {
      inherit stdenv fetchurl fuse;
    };

  This saves a lot of typing (not to mention not having to update
  all-packages.nix with purely mechanical changes).  It saves as much
  typing as the "args: with args;" style, but has the advantage that
  the function arguments are properly declared (not implicit in what
  the body of the "with" uses).

1 files changed, 3 insertions, 1 deletions

diff --git a/src/libexpr/expr-to-xml.cc b/src/libexpr/expr-to-xml.cc
index 6ec906356a..e401001ead 100644
--- a/src/libexpr/expr-to-xml.cc
+++ b/src/libexpr/expr-to-xml.cc
@@ -45,15 +45,17 @@ static void printPatternAsXML(Pattern pat, XMLWriter & doc)
     ATerm name;
     ATermList formals;
     Pattern pat1, pat2;
+    ATermBool ellipsis;
     if (matchVarPat(pat, name))
         doc.writeEmptyElement("varpat", singletonAttrs("name", aterm2String(name)));
-    else if (matchAttrsPat(pat, formals)) {
+    else if (matchAttrsPat(pat, formals, ellipsis)) {
         XMLOpenElement _(doc, "attrspat");
         for (ATermIterator i(formals); i; ++i) {
             Expr name; ATerm dummy;
             if (!matchFormal(*i, name, dummy)) abort();
             doc.writeEmptyElement("attr", singletonAttrs("name", aterm2String(name)));
         }
+        if (ellipsis == eTrue) doc.writeEmptyElement("ellipsis");
     }
     else if (matchAtPat(pat, pat1, pat2)) {
         XMLOpenElement _(doc, "at");