diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index b9dd4c7695d..07f084fe5be 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -27,7 +27,7 @@ walktype(Node *n, int top)
 	Type *t;
 	Sym *s;
 	long lno;
-	int et;
+	int et, cl, cr;
 
 	/*
 	 * walk the whole tree of the body of a function.
@@ -229,29 +229,47 @@ loop:
 
 		l = n->left;
 		r = n->right;
-		if(l == N)
-			goto ret;
 
 		walktype(l, Elv);
-		walktype(r, Erv);
-		if(l == N || l->type == T)
+		if(l == N || r == N)
 			goto ret;
 
-		convlit(r, l->type);
-		if(r == N || r->type == T)
-			goto ret;
+		cl = listcount(l);
+		cr = listcount(r);
 
-		if(r->op == OCALL && l->op == OLIST) {
+		if(cl == cr) {
+			walktype(r, Erv);
+			l = ascompatee(n->op, &n->left, &n->right);
+			if(l != N)
+				*n = *reorder3(l);
+			goto ret;
+		}
+
+		if(cr != 1) {
+			yyerror("bad shape across assignment");
+			goto ret;
+		}
+
+		switch(r->op) {
+		case OCALLMETH:
+		case OCALLINTER:
+		case OCALL:
+			walktype(r, Erv);
 			l = ascompatet(n->op, &n->left, &r->type, 0);
 			if(l != N) {
 				*n = *nod(OLIST, r, reorder2(l));
 			}
-			goto ret;
-		}
+			break;
 
-		l = ascompatee(n->op, &n->left, &n->right);
-		if(l != N)
-			*n = *reorder3(l);
+		case OINDEX:
+		case OINDEXPTR:
+			if(!isptrto(r->left->type, TMAP))
+				goto badt;
+			if(cl != 2)
+				goto badt;
+			*n = *mapop(n, top);
+			break;
+		}
 		goto ret;
 
 	case OBREAK:
@@ -1412,40 +1430,6 @@ mapop(Node *n, int top)
 		a = n->left;				// map
 		r = nod(OLIST, a, r);
 
-		on = syslook("mapaccess1", 1);
-
-		argtype(on, t->down);	// any-1
-		argtype(on, t->type);	// any-2
-		argtype(on, t->down);	// any-3
-		argtype(on, t->type);	// any-4
-
-		r = nod(OCALL, on, r);
-		walktype(r, Erv);
-		r->type = t->type;
-		break;
-
-		// mapaccess2(hmap *map[any]any, key any) (val any, pres bool);
-
-		t = fixmap(n->left->type);
-		if(t == T)
-			break;
-
-		convlit(n->right, t->down);
-
-		if(!eqtype(n->right->type, t->down, 0)) {
-			badtype(n->op, n->right->type, t->down);
-			break;
-		}
-
-		a = n->right;				// key
-		if(!isptr[t->down->etype]) {
-			a = nod(OADDR, a, N);
-			a->type = ptrto(t);
-		}
-		r = a;
-		a = n->left;				// map
-		r = nod(OLIST, a, r);
-
 		on = syslook("mapaccess2", 1);
 
 		argtype(on, t->down);	// any-1
@@ -1458,9 +1442,36 @@ mapop(Node *n, int top)
 		r->type = t->type;
 		break;
 
+	access2:
+		// mapaccess2(hmap *map[any-1]any-2, key any-3) (val-4 any, pres bool);
+
+		t = fixmap(n->right->left->type);
+		if(t == T)
+			break;
+
+		a = n->right->right;			// key
+		r = a;
+		a = n->right->left;			// map
+		r = nod(OLIST, a, r);
+
+		on = syslook("mapaccess2", 1);
+
+		argtype(on, t->down);	// any-1
+		argtype(on, t->type);	// any-2
+		argtype(on, t->down);	// any-3
+		argtype(on, t->type);	// any-4
+
+		n->right = nod(OCALL, on, r);
+		walktype(n, Etop);
+		r = n;
+		break;
+
 	case OAS:
-		if(top != Elv)
+		if(top != Elv) {
+			if(top == Etop)
+				goto access2;
 			goto nottop;
+		}
 		if(n->left->op != OINDEX)
 			fatal("mapos: AS left not OINDEX");
 
@@ -1661,7 +1672,7 @@ colas(Node *nl, Node *nr)
 	/* nl is an expression list.
 	 * nr is an expression list.
 	 * return a newname-list from
-	 * the types from the rhs.
+	 * types derived from the rhs.
 	 */
 	n = N;
 	cr = listcount(nr);
@@ -1675,21 +1686,19 @@ colas(Node *nl, Node *nr)
 	l = listfirst(&savel, &nl);
 	r = listfirst(&saver, &nr);
 
-loop:
-	if(l == N)
-		return n;
+	while(l != N) {
+		walktype(r, Erv);
+		defaultlit(r);
+		a = old2new(l, r->type);
+		if(n == N)
+			n = a;
+		else
+			n = nod(OLIST, n, a);
 
-	walktype(r, Erv);
-	defaultlit(r);
-	a = old2new(l, r->type);
-	if(n == N)
-		n = a;
-	else
-		n = nod(OLIST, n, a);
-
-	l = listnext(&savel);
-	r = listnext(&saver);
-	goto loop;
+		l = listnext(&savel);
+		r = listnext(&saver);
+	}
+	return n;
 
 multi:
 	/*
@@ -1738,9 +1747,9 @@ multi:
 		if(t == T || t->etype != TMAP)
 			goto badt;
 
-		a = old2new(nl->left, types[TBOOL]);
+		a = old2new(nl->left, t->type);
 		n = a;
-		a = old2new(nl->right, t->type);
+		a = old2new(nl->right, types[TBOOL]);
 		n = nod(OLIST, n, a);
 		break;
 	}
diff --git a/src/runtime/runtime.c b/src/runtime/runtime.c
index e8c18385926..2c1acadec66 100644
--- a/src/runtime/runtime.c
+++ b/src/runtime/runtime.c
@@ -764,3 +764,362 @@ check(void)
 //	prints(1"check ok\n");
 	initsig();
 }
+
+typedef	struct	Link	Link;
+typedef	struct	Hmap	Hmap;
+typedef	struct	Alg	Alg;
+
+struct	Alg
+{
+	uint64	(*hash)(uint32, void*);
+	uint32	(*equal)(uint32, void*, void*);
+	void	(*print)(uint32, void*);
+	void	(*copy)(uint32, void*, void*);
+};
+
+struct	Link
+{
+	Link*	link;
+	byte	data[8];
+};
+
+struct	Hmap
+{
+	uint32	keysize;
+	uint32	valsize;
+	uint32	hint;
+	Alg*	keyalg;
+	Alg*	valalg;
+	uint32	valoffset;
+	uint32	ko;
+	uint32	vo;
+	uint32	po;
+	Link*	link;
+};
+
+static uint64
+memhash(uint32 s, void *a)
+{
+	prints("memhash\n");
+	return 0x12345;
+}
+
+static uint32
+memequal(uint32 s, void *a, void *b)
+{
+	byte *ba, *bb;
+	uint32 i;
+
+	ba = a;
+	bb = b;
+	for(i=0; i<s; i++)
+		if(ba[i] != bb[i])
+			return 0;
+	return 1;
+}
+
+static void
+memprint(uint32 s, void *a)
+{
+	uint64 v;
+
+	v = 0xbadb00b;
+	switch(s) {
+	case 1:
+		v = *(uint8*)a;
+		break;
+	case 2:
+		v = *(uint16*)a;
+		break;
+	case 4:
+		v = *(uint32*)a;
+		break;
+	case 8:
+		v = *(uint64*)a;
+		break;
+	}
+	sys_printint(v);
+}
+
+static void
+memcopy(uint32 s, void *a, void *b)
+{
+	byte *ba, *bb;
+	uint32 i;
+
+	ba = a;
+	bb = b;
+	if(bb == nil) {
+		for(i=0; i<s; i++)
+			ba[i] = 0;
+		return;
+	}
+	for(i=0; i<s; i++)
+		ba[i] = bb[i];
+}
+
+static uint64
+stringhash(uint32 s, string *a)
+{
+	prints("stringhash\n");
+	return 0x12345;
+}
+
+static uint32
+stringequal(uint32 s, string *a, string *b)
+{
+	return cmpstring(*a, *b) == 0;
+}
+
+static void
+stringprint(uint32 s, string *a)
+{
+	sys_printstring(*a);
+}
+
+static void
+stringcopy(uint32 s, string *a, string *b)
+{
+	if(b == nil) {
+		*b = nil;
+		return;
+	}
+	*a = *b;
+}
+
+static uint32
+rnd(uint32 n, uint32 m)
+{
+	uint32 r;
+
+	r = n % m;
+	if(r)
+		n += m-r;
+	return n;
+}
+
+static	Alg
+algarray[] =
+{
+	{	&memhash,	&memequal,	&memprint,	&memcopy	},
+	{	&stringhash,	&stringequal,	&stringprint,	&stringcopy	},
+};
+
+// newmap(keysize uint32, valsize uint32,
+//	keyalg uint32, valalg uint32,
+//	hint uint32) (hmap *map[any]any);
+void
+sys_newmap(uint32 keysize, uint32 valsize,
+	uint32 keyalg, uint32 valalg, uint32 hint,
+	Hmap* ret)
+{
+	Hmap *m;
+
+	if(keyalg >= nelem(algarray) ||
+	   valalg >= nelem(algarray)) {
+		prints("0<=");
+		sys_printint(keyalg);
+		prints("<");
+		sys_printint(nelem(algarray));
+		prints("\n0<=");
+		sys_printint(valalg);
+		prints("<");
+		sys_printint(nelem(algarray));
+		prints("\n");
+
+		throw("sys_newmap: key/val algorithm out of range");
+	}
+
+	m = mal(sizeof(*m));
+
+	m->keysize = keysize;
+	m->valsize = valsize;
+	m->keyalg = &algarray[keyalg];
+	m->valalg = &algarray[valalg];
+	m->hint = hint;
+
+	// these calculations are compiler dependent
+	m->valoffset = rnd(keysize, valsize);
+	m->ko = rnd(sizeof(m), keysize);
+	m->vo = rnd(m->ko+keysize, valsize);
+	m->po = rnd(m->vo+valsize, 1);
+
+	ret = m;
+	FLUSH(&ret);
+
+	if(debug) {
+		prints("newmap: map=");
+		sys_printpointer(m);
+		prints("; keysize=");
+		sys_printint(keysize);
+		prints("; valsize=");
+		sys_printint(valsize);
+		prints("; keyalg=");
+		sys_printint(keyalg);
+		prints("; valalg=");
+		sys_printint(valalg);
+		prints("; valoffset=");
+		sys_printint(m->valoffset);
+		prints("; ko=");
+		sys_printint(m->ko);
+		prints("; vo=");
+		sys_printint(m->vo);
+		prints("; po=");
+		sys_printint(m->po);
+		prints("\n");
+	}
+}
+
+// mapaccess1(hmap *map[any]any, key any) (val any);
+void
+sys_mapaccess1(Hmap *m, ...)
+{
+	Link *l;
+	byte *ak, *av;
+
+	ak = (byte*)&m + m->ko;
+	av = (byte*)&m + m->vo;
+
+	for(l=m->link; l!=nil; l=l->link) {
+		if(m->keyalg->equal(m->keysize, ak, l->data)) {
+			m->valalg->copy(m->valsize, av, l->data+m->valoffset);
+			goto out;
+		}
+	}
+
+	m->valalg->copy(m->valsize, av, 0);
+
+out:
+	if(1) {
+		prints("sys_mapaccess1: map=");
+		sys_printpointer(m);
+		prints("; key=");
+		m->keyalg->print(m->keysize, ak);
+		prints("; val=");
+		m->valalg->print(m->valsize, av);
+		prints("\n");
+	}
+}
+
+// mapaccess2(hmap *map[any]any, key any) (val any, pres bool);
+void
+sys_mapaccess2(Hmap *m, ...)
+{
+	Link *l;
+	byte *ak, *av, *ap;
+
+	ak = (byte*)&m + m->ko;
+	av = (byte*)&m + m->vo;
+	ap = (byte*)&m + m->po;
+
+	for(l=m->link; l!=nil; l=l->link) {
+		if(m->keyalg->equal(m->keysize, ak, l->data)) {
+			*ap = true;
+			m->valalg->copy(m->valsize, av, l->data+m->valoffset);
+			goto out;
+		}
+	}
+
+	*ap = false;
+	m->valalg->copy(m->valsize, av, nil);
+
+out:
+	if(debug) {
+		prints("sys_mapaccess2: map=");
+		sys_printpointer(m);
+		prints("; key=");
+		m->keyalg->print(m->keysize, ak);
+		prints("; val=");
+		m->valalg->print(m->valsize, av);
+		prints("; pres=");
+		sys_printbool(*ap);
+		prints("\n");
+	}
+}
+
+static void
+sys_mapassign(Hmap *m, byte *ak, byte *av)
+{
+	Link *l;
+
+	// mapassign(hmap *map[any]any, key any, val any);
+
+	for(l=m->link; l!=nil; l=l->link) {
+		if(m->keyalg->equal(m->keysize, ak, l->data))
+			goto out;
+	}
+
+	l = mal((sizeof(*l)-8) + m->keysize + m->valsize);
+	l->link = m->link;
+	m->link = l;
+	m->keyalg->copy(m->keysize, l->data, ak);
+
+out:
+	m->valalg->copy(m->valsize, l->data+m->valoffset, av);
+
+	if(debug) {
+		prints("mapassign: map=");
+		sys_printpointer(m);
+		prints("; key=");
+		m->keyalg->print(m->keysize, ak);
+		prints("; val=");
+		m->valalg->print(m->valsize, av);
+		prints("\n");
+	}
+}
+
+// mapassign1(hmap *map[any]any, key any, val any);
+void
+sys_mapassign1(Hmap *m, ...)
+{
+	Link **ll;
+	byte *ak, *av;
+
+	ak = (byte*)&m + m->ko;
+	av = (byte*)&m + m->vo;
+
+	sys_mapassign(m, ak, av);
+}
+
+// mapassign2(hmap *map[any]any, key any, val any, pres bool);
+void
+sys_mapassign2(Hmap *m, ...)
+{
+	Link **ll;
+	byte *ak, *av, *ap;
+
+
+	ak = (byte*)&m + m->ko;
+	av = (byte*)&m + m->vo;
+	ap = (byte*)&m + m->po;
+
+	if(*ap == true) {
+		// assign
+		sys_mapassign(m, ak, av);
+		return;
+	}
+
+	// delete
+	for(ll=&m->link; (*ll)!=nil; ll=&(*ll)->link) {
+		if(m->keyalg->equal(m->keysize, ak, (*ll)->data)) {
+			m->valalg->copy(m->valsize, (*ll)->data+m->valoffset, nil);
+			(*ll) = (*ll)->link;
+			if(debug) {
+				prints("mapdelete (found): map=");
+				sys_printpointer(m);
+				prints("; key=");
+				m->keyalg->print(m->keysize, ak);
+				prints("\n");
+			}
+			return;
+		}
+	}
+
+	if(debug) {
+		prints("mapdelete (not found): map=");
+		sys_printpointer(m);
+		prints("; key=");
+		m->keyalg->print(m->keysize, ak);
+		prints(" *** not found\n");
+	}
+}