* 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, 18 insertions, 6 deletions

diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index c48aa34aaf..b7624df7e8 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -208,16 +208,22 @@ static void freeAndUnprotect(void * p)
 %union {
   ATerm t;
   ATermList ts;
+  struct {
+    ATermList formals;
+    bool ellipsis;
+  } formals;
 }
 
 %type <t> start expr expr_function expr_if expr_op
 %type <t> expr_app expr_select expr_simple bind inheritsrc formal
 %type <t> pattern pattern2
-%type <ts> binds ids expr_list formals string_parts ind_string_parts
+%type <ts> binds ids expr_list string_parts ind_string_parts
+%type <formals> formals
 %token <t> ID INT STR IND_STR PATH URI
 %token IF THEN ELSE ASSERT WITH LET IN REC INHERIT EQ NEQ AND OR IMPL
 %token DOLLAR_CURLY /* == ${ */
 %token IND_STRING_OPEN IND_STRING_CLOSE
+%token ELLIPSIS
 
 %nonassoc IMPL
 %left OR
@@ -326,7 +332,7 @@ pattern
 
 pattern2
   : ID { $$ = makeVarPat($1); }
-  | '{' formals '}' { $$ = makeAttrsPat($2); }
+  | '{' formals '}' { $$ = makeAttrsPat($2.formals, $2.ellipsis ? eTrue : eFalse); }
   ;
 
 binds
@@ -357,9 +363,14 @@ expr_list
   ;
 
 formals
-  : formal ',' formals { $$ = ATinsert($3, $1); } /* idem - right recursive */
-  | formal { $$ = ATinsert(ATempty, $1); }
-  | { $$ = ATempty; }
+  : formal ',' formals /* idem - right recursive */
+    { $$.formals = ATinsert($3.formals, $1); $$.ellipsis = $3.ellipsis; }
+  | formal
+    { $$.formals = ATinsert(ATempty, $1); $$.ellipsis = false; }
+  |
+    { $$.formals = ATempty; $$.ellipsis = false; }
+  | ELLIPSIS
+    { $$.formals = ATempty; $$.ellipsis = true; }
   ;
 
 formal
@@ -401,13 +412,14 @@ static void checkPatternVars(ATerm pos, ATermMap & map, Pattern pat)
     ATerm name;
     ATermList formals;
     Pattern pat1, pat2;
+    ATermBool ellipsis;
     if (matchVarPat(pat, name)) {
         if (map.get(name))
             throw EvalError(format("duplicate formal function argument `%1%' at %2%")
                 % aterm2String(name) % showPos(pos));
         map.set(name, name);
     }
-    else if (matchAttrsPat(pat, formals)) { 
+    else if (matchAttrsPat(pat, formals, ellipsis)) { 
         for (ATermIterator i(formals); i; ++i) {
             ATerm d1;
             if (!matchFormal(*i, name, d1)) abort();