PATCH: Add :^ syntax for zipping two arrays

[Mikael Magnusson <mikachu@xxxxxxxxx>]

Any objections to adding this? Comments on the code is also welcome
since I'm not at all sure I thought of all the gotchas in paramsubst(),
in particular some allocations might be leaking? Not adding tests until
any and all comments are incorporated.

---
 Doc/Zsh/expn.yo | 12 ++++++++++++
 Src/subst.c     | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/Doc/Zsh/expn.yo b/Doc/Zsh/expn.yo
index ff9f2b1..2fb803a 100644
--- a/Doc/Zsh/expn.yo
+++ b/Doc/Zsh/expn.yo
@@ -636,6 +636,18 @@ Similar to the preceding subsitution, but in the opposite sense,
 so that entries present in both the original substitution and as
 elements of var(arrayname) are retained and others removed.
 )
+item(tt(${)var(name)tt(:^)var(arrayname)tt(}))(
+Zips two arrays, such that the output array is twice as long as the
+longest of tt(name) and tt(arrayname), with the elements alternatingly
+being picked from them. If one of the input arrays is shorter, then the
+input is repeated until all of the other array has been used up.  Thus,
+
+example(a=(1 2 3 4); b=(a b); print ${a:^b})
+
+will output `tt(1 a 2 b 3 a 4 b)'. Either or both inputs may be a scalar,
+they will be treated as an array of length 1 with the scalar as the only
+element.
+)
 xitem(tt(${)var(name)tt(:)var(offset)tt(}))
 item(tt(${)var(name)tt(:)var(offset)tt(:)var(length)tt(}))(
 This syntax gives effects similar to parameter subscripting
diff --git a/Src/subst.c b/Src/subst.c
index d4b68e2..a66ce01 100644
--- a/Src/subst.c
+++ b/Src/subst.c
@@ -2878,6 +2878,57 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags)
 	    }
 	    break;
 	}
+    } else if (inbrace && (*s == '^' || *s == Hat)) {
+	char **zip, **ap, **apsrc;
+	++s;
+	if (*itype_end(s, IIDENT, 0)) {
+	    untokenize(s);
+	    zerr("not an identifier: %s", s);
+	    return NULL;
+	}
+	if (vunset) {
+	    if (unset(UNSET)) {
+		*idend = '\0';
+		zerr("%s: parameter not set", idbeg);
+		return NULL;
+	    }
+	    val = dupstring("");
+	} else {
+	    char *sval;
+	    zip = getaparam(s);
+	    if (!zip) {
+		sval = getsparam(s);
+		if (sval)
+		    zip = mkarray(sval);
+	    }
+	    if (!isarr) aval = mkarray(val);
+	    if (zip) {
+		char **out;
+		int alen, ziplen, outlen, i = 0;
+		alen = arrlen(aval);
+		ziplen = arrlen(zip);
+		outlen = alen > ziplen ? alen : ziplen;
+		out = zalloc(sizeof(char *) * (2 * outlen + 1));
+		while (i < outlen) {
+		    if (copied)
+			out[i*2] = aval[i % alen];
+		    else
+			out[i*2] = ztrdup(aval[i % alen]);
+		    out[i*2+1] = ztrdup(zip[i % ziplen]);
+		    i++;
+		}
+		out[i*2] = NULL;
+		aval = out;
+		copied = 1;
+		isarr = 1;
+	    } else {
+		if (unset(UNSET)) {
+		    zerr("%s: parameter not set", s);
+		    return NULL;
+		}
+		val = dupstring("");
+	    }
+	}
     } else if (inbrace && (*s == '|' || *s == Bar ||
 			   *s == '*' || *s == Star)) {
 	int intersect = (*s == '*' || *s == Star);
-- 
1.9.0