diff --git a/ucl/builtins.go b/ucl/builtins.go
index 0c84824..e1edbcc 100644
--- a/ucl/builtins.go
+++ b/ucl/builtins.go
@@ -539,6 +539,39 @@ func indexLookup(ctx context.Context, obj, elem Object, pos lexer.Position) (Obj
 	return nil, nil
 }
 
+func indexAssign(ctx context.Context, obj, elem, toVal Object, pos lexer.Position) (_ Object, err error) {
+	if obj == nil {
+		return nil, assignToNilIndex(pos)
+	}
+	switch v := obj.(type) {
+	case ModListable:
+		intIdx, ok := elem.(IntObject)
+		if !ok {
+			return nil, nil
+		}
+		if int(intIdx) >= 0 && int(intIdx) < v.Len() {
+			err = v.SetIndex(int(intIdx), toVal)
+		} else if int(intIdx) < 0 && int(intIdx) >= -v.Len() {
+			err = v.SetIndex(v.Len()+int(intIdx), toVal)
+		}
+		if err != nil {
+			return nil, err
+		}
+		return toVal, nil
+	case ModHashable:
+		strIdx, ok := elem.(StringObject)
+		if !ok {
+			return nil, nil
+		}
+		err = v.SetValue(string(strIdx), toVal)
+		if err != nil {
+			return nil, err
+		}
+		return toVal, nil
+	}
+	return nil, notModIndexableError(pos)
+}
+
 func indexBuiltin(ctx context.Context, args invocationArgs) (Object, error) {
 	if err := args.expectArgn(1); err != nil {
 		return nil, err
diff --git a/ucl/builtins_test.go b/ucl/builtins_test.go
index effb183..4a099f9 100644
--- a/ucl/builtins_test.go
+++ b/ucl/builtins_test.go
@@ -295,53 +295,53 @@ func TestBuiltins_While(t *testing.T) {
 		want string
 	}{
 		{desc: "iterate while true 1", expr: `
-			$x = 0	
+			x = 0	
 			while (lt $x 5) {
 				echo $x
-				$x = (add $x 1)
+				x = add $x 1
 			}
 			echo "done"`, want: "0\n1\n2\n3\n4\ndone\n(nil)\n"},
 		{desc: "iterate while true 2", expr: `
-			$x = 20	
+			x = 20	
 			while (lt $x 5) {
 				echo $x
-				$x = (add $x 1)
+				x = (add $x 1)
 			}
 			echo "done"`, want: "done\n(nil)\n"},
 		{desc: "iterate while true with pipeline", expr: `
-			$x = 0
+			x = 0
 			while (lt $x 5) {
 				echo $x
-				$x = (add $x 1)
+				x = (add $x 1)
 				if (ge $x 3) {
 					break "Ahh"
 				}
 			} | echo " was the break"
 			echo "done"`, want: "0\n1\n2\nAhh was the break\ndone\n(nil)\n"},
 		{desc: "iterate for ever with break 1", expr: `
-			$x = 0
+			x = 0
 			while {
 				echo $x
-				$x = (add $x 1)
+				x = add $x 1
 				if (ge $x 5) {
 					break
 				}
 			}
 			echo "done"`, want: "0\n1\n2\n3\n4\ndone\n(nil)\n"},
 		{desc: "iterate for ever with break 2", expr: `
-			$x = 0
+			x = 0
 			echo (while {
 				echo $x
-				$x = add $x 1
+				x = add $x 1
 				if (ge $x 5) {
 					break $x
 				}
 			})
 			`, want: "0\n1\n2\n3\n4\n5\n(nil)\n"},
 		{desc: "iterate for ever with continue", expr: `
-			$x = 0
+			x = 0
 			while {
-				$x = (add $x 1)
+				x = (add $x 1)
 				if (or (eq $x 2) (eq $x 4)) {
 					echo "quack"
 					continue
@@ -501,10 +501,10 @@ func TestBuiltins_Procs(t *testing.T) {
 				}
 			}
 
-			$helloGreater = makeGreeter "Hello"
+			helloGreater = makeGreeter "Hello"
 			$helloGreater "world"
 
-			$goodbye = makeGreeter "Goodbye cruel"
+			goodbye = makeGreeter "Goodbye cruel"
 			$goodbye "world"
 
 			call (makeGreeter "Quick") ["call me"]
@@ -512,13 +512,13 @@ func TestBuiltins_Procs(t *testing.T) {
 			`, want: "Hello, world\nGoodbye cruel, world\nQuick, call me\n(nil)\n"},
 		{desc: "modifying closed over variables", expr: `
 			proc makeSetter {
-				$bla = "X"
+				bla = "X"
 				proc appendToBla { |x|
-					$bla = cat $bla $x
+					bla = cat $bla $x
 				}
 			}
 		
-			$er = makeSetter
+			er = makeSetter
 			echo (call $er ["xxx"])
 			echo (call $er ["yyy"])
 			`, want: "Xxxx\nXxxxyyy\n(nil)\n"},
@@ -623,7 +623,7 @@ func TestBuiltins_Return(t *testing.T) {
 				echo "world"
 			}
 			proc greet {
-				$what = (greetWhat)
+				what = (greetWhat)
 				echo "Hello, " $what
 			}
 
@@ -687,7 +687,7 @@ func TestBuiltins_Return(t *testing.T) {
 
 			proc test-thing {
 				for [1 2 3] { |x|
-					$myClosure = proc { echo $x }
+					myClosure = proc { echo $x }
 					do-thing $myClosure
 				}
 			}
@@ -714,12 +714,12 @@ func TestBuiltins_Return(t *testing.T) {
 
 			proc test-thing {	
 				[1 2 3] | map { |x|
-					$myProc = proc { echo $x }
+					myProc = proc { echo $x }
 					proc { do-thing $myProc }
 				}
 			}
 
-			$hello = "xx"
+			hello = "xx"
 			for (test-thing) { |y| call $y ; echo $hello }
 		`, want: "1\nxx\n2\nxx\n3\nxx\n(nil)\n"},
 		{desc: "check closure 7", expr: `
@@ -728,15 +728,15 @@ func TestBuiltins_Return(t *testing.T) {
 			}
 
 			proc test-thing {
-				$f = 0
+				f = 0
 				[1 2 3] | map { |x|
-					$myProc = proc { echo $f }
-					$f = (add $f 1)
+					myProc = proc { echo $f }
+					f = (add $f 1)
 					proc { do-thing $myProc }	
 				}
 			}
 
-			$hello = "xx"
+			hello = "xx"
 			for (test-thing) { |y| call $y ; echo $hello }
 		`, want: "3\nxx\n3\nxx\n3\nxx\n(nil)\n"},
 		{desc: "check closure 7", expr: `
@@ -745,16 +745,16 @@ func TestBuiltins_Return(t *testing.T) {
 			}
 
 			proc test-thing {
-				$f = 1
+				f = 1
 				[1 2 3] | map { |x|
-					$g = $f
-					$myProc = (proc { echo $g })	
-					$f = (add $f 1)
+					g = $f
+					myProc = (proc { echo $g })	
+					f = (add $f 1)
 					proc { do-thing $myProc }	
 				}
 			}
 
-			$hello = "xx"
+			hello = "xx"
 			for (test-thing) { |y| call $y ; echo $hello }
 		`, want: "1\nxx\n2\nxx\n3\nxx\n(nil)\n"},
 	}
@@ -917,11 +917,11 @@ func TestBuiltins_Try(t *testing.T) {
 			}
 		`, want: "Hello\nCatch me: bang\nAlways\n", wantErr: "boom"},
 		{desc: "try 12", expr: `
-			$a = try { "e" } catch { "f" }
+			a = try { "e" } catch { "f" }
 			echo $a
 		`, want: "e\n(nil)\n"},
 		{desc: "try 13", expr: `
-			$a = try { error "bang" } catch { "f" }
+			a = try { error "bang" } catch { "f" }
 			echo $a
 		`, want: "f\n(nil)\n"},
 		{desc: "try 14", expr: `
@@ -1081,12 +1081,12 @@ func TestBuiltins_Map(t *testing.T) {
 			map ["a" "b" "c"] (proc { |x| makeUpper $x }) 
 			`, want: "A\nB\nC\n"},
 		{desc: "map list 2", expr: `
-			$makeUpper = proc { |x| $x | toUpper }
+			makeUpper = proc { |x| $x | toUpper }
 
 			map ["a" "b" "c"] $makeUpper 
 			`, want: "A\nB\nC\n"},
 		{desc: "map list with pipe", expr: `
-			$makeUpper = proc { |x| $x | toUpper }
+			makeUpper = proc { |x| $x | toUpper }
 
 			["a" "b" "c"] | map $makeUpper 
 			`, want: "A\nB\nC\n"},
@@ -1094,15 +1094,15 @@ func TestBuiltins_Map(t *testing.T) {
 			map ["a" "b" "c"] { |x| toUpper $x } 
 			`, want: "A\nB\nC\n"},
 		{desc: "map list with stream", expr: `
-			$makeUpper = proc { |x| toUpper $x }
+			makeUpper = proc { |x| toUpper $x }
 		
-			$l = ["a" "b" "c"] | map $makeUpper
+			l = ["a" "b" "c"] | map $makeUpper
 			echo $l
 			`, want: "[A B C]\n(nil)\n"},
 		{desc: "map itr stream", expr: `
-			$add2 = proc { |x| add $x 2 }
+			add2 = proc { |x| add $x 2 }
 		
-			$l = itr | map $add2
+			l = itr | map $add2
 			for $l { |x| echo $x }
 			`, want: "3\n4\n5\n(nil)\n"},
 	}
@@ -1356,7 +1356,7 @@ func TestBuiltins_Filter(t *testing.T) {
 		}},
 		{desc: "filter map 3", expr: `filter [alpha:"hello" bravo:"world"] { |k v| eq $v "alpha" }`, want: map[string]any{}},
 
-		{desc: "filter itr 1", expr: `$s = "" ; itr | filter { |x| ne $x 2 } | for { |x| $s = "$s $x" }; $s`, want: " 1 3"},
+		{desc: "filter itr 1", expr: `s = "" ; itr | filter { |x| ne $x 2 } | for { |x| s = "$s $x" }; $s`, want: " 1 3"},
 	}
 
 	for _, tt := range tests {
@@ -1408,10 +1408,10 @@ func TestBuiltins_Head(t *testing.T) {
 		{desc: "head list 1", expr: `head [1 2 3]`, want: 1},
 
 		{desc: "head itr 1", expr: `head (itr)`, want: 1},
-		{desc: "head itr 2", expr: `$h = (itr) ; head $h`, want: 1},
-		{desc: "head itr 3", expr: `$h = (itr) ; head $h ; head $h`, want: 2},
-		{desc: "head itr 4", expr: `$h = (itr) ; head $h ; head $h ; head $h`, want: 3},
-		{desc: "head itr 5", expr: `$h = (itr) ; head $h ; head $h ; head $h ; head $h`, want: nil},
+		{desc: "head itr 2", expr: `h = (itr) ; head $h`, want: 1},
+		{desc: "head itr 3", expr: `h = (itr) ; head $h ; head $h`, want: 2},
+		{desc: "head itr 4", expr: `h = (itr) ; head $h ; head $h ; head $h`, want: 3},
+		{desc: "head itr 5", expr: `h = (itr) ; head $h ; head $h ; head $h ; head $h`, want: nil},
 	}
 
 	for _, tt := range tests {
@@ -1747,7 +1747,7 @@ func TestBuiltins_Cat(t *testing.T) {
 		{desc: "cat 6", expr: `cat "array = " [1 3 2 4]`, want: "array = [1 3 2 4]"},
 		{desc: "cat 7", expr: `cat 1 $true 3 [4]`, want: "1true3[4]"},
 		{desc: "cat 8", expr: `cat`, want: ""},
-		{desc: "cat 9", expr: `$x = ["a" "b" "c"] ; cat "array = " [1 $x.(0) $x.(2) $x.(1)]`, want: "array = [1 a c b]"},
+		{desc: "cat 9", expr: `x = ["a" "b" "c"] ; cat "array = " [1 $x.(0) $x.(2) $x.(1)]`, want: "array = [1 a c b]"},
 	}
 
 	for _, tt := range tests {
diff --git a/ucl/errors.go b/ucl/errors.go
index f7f80e9..8e20adb 100644
--- a/ucl/errors.go
+++ b/ucl/errors.go
@@ -14,6 +14,8 @@ var (
 var (
 	tooManyFinallyBlocksError = newBadUsage("try needs at most 1 finally")
 	notIndexableError         = newBadUsage("index only support on lists and hashes")
+	notModIndexableError      = newBadUsage("list or hash cannot be modified")
+	assignToNilIndex          = newBadUsage("assigning to nil index value")
 )
 
 type errorWithPos struct {
diff --git a/ucl/eval.go b/ucl/eval.go
index 82313df..c6469ae 100644
--- a/ucl/eval.go
+++ b/ucl/eval.go
@@ -220,7 +220,51 @@ func (e evaluator) assignDot(ctx context.Context, ec *evalCtx, n astDot, toVal O
 		return e.assignArg(ctx, ec, n.Arg, toVal)
 	}
 
-	return nil, errors.New("TODO")
+	val, err := e.evalArgForDotAssign(ctx, ec, n.Arg)
+	if err != nil {
+		return nil, err
+	}
+
+	for i, dot := range n.DotSuffix {
+		isLast := i == len(n.DotSuffix)-1
+
+		var idx Object
+		if dot.KeyIdent != nil {
+			idx = StringObject(dot.KeyIdent.String())
+		} else {
+			idx, err = e.evalPipeline(ctx, ec, dot.Pipeline)
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		if isLast {
+			val, err = indexAssign(ctx, val, idx, toVal, n.Pos)
+		} else {
+			val, err = indexLookup(ctx, val, idx, n.Pos)
+		}
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return val, nil
+}
+
+func (e evaluator) evalArgForDotAssign(ctx context.Context, ec *evalCtx, n astCmdArg) (Object, error) {
+	// Special case for dot assigns of 'a.b = c' where a is actually a var deref (i.e. $a)
+	// which is unnecessary for assignments. Likewise, having '$a.b = c' should be dissallowed
+
+	switch {
+	case n.Ident != nil:
+		if v, ok := ec.getVar(n.Ident.String()); ok {
+			return v, nil
+		}
+		return nil, nil
+	case n.Var != nil:
+		return nil, errors.New("cannot assign to a dereferenced variable")
+	}
+	return e.evalArg(ctx, ec, n)
 }
 
 func (e evaluator) evalArg(ctx context.Context, ec *evalCtx, n astCmdArg) (Object, error) {
@@ -266,8 +310,7 @@ func (e evaluator) assignArg(ctx context.Context, ec *evalCtx, n astCmdArg, toVa
 	case n.Literal != nil:
 		return nil, errors.New("cannot assign to a literal value")
 	case n.Var != nil:
-		ec.setOrDefineVar(*n.Var, toVal)
-		return toVal, nil
+		return nil, errors.New("cannot assign to a dereferenced variable")
 	case n.PseudoVar != nil:
 		pvar, ok := ec.getPseudoVar(*n.PseudoVar)
 		if ok {
diff --git a/ucl/inst_test.go b/ucl/inst_test.go
index 718d0b7..041c367 100644
--- a/ucl/inst_test.go
+++ b/ucl/inst_test.go
@@ -27,15 +27,15 @@ func TestInst_Eval(t *testing.T) {
 		{desc: "simple ident 1", expr: `firstarg a-test`, want: "a-test"},
 
 		// String interpolation
-		{desc: "interpolate string 1", expr: `$what = "world" ; firstarg "hello $what"`, want: "hello world"},
-		{desc: "interpolate string 2", expr: `$what = "world" ; $when = "now" ; firstarg "$when, hello $what"`, want: "now, hello world"},
-		{desc: "interpolate string 3", expr: `$what = "world" ; $when = "now" ; firstarg "${when}, hello ${what}"`, want: "now, hello world"},
-		{desc: "interpolate string 4", expr: `$crazy = [far: "unknown"] ; firstarg "hello ${crazy.far}"`, want: "hello unknown"},
-		{desc: "interpolate string 5", expr: `$oldWords = ["hither" "thither" "yonder"] ; firstarg "hello ${oldWords.(1)}"`, want: "hello thither"},
-		{desc: "interpolate string 6", expr: `$oldWords = ["hither" "thither" "yonder"] ; firstarg "hello ${oldWords.(add 1 1)}"`, want: "hello yonder"},
-		{desc: "interpolate string 7", expr: `$oldWords = ["hither" "thither" "yonder"] ; firstarg "hello ${oldWords.(add 2 | sub (sub 2 1) | sub 1)}"`, want: "hello hither"},
-		{desc: "interpolate string 8", expr: `$words = ["old": ["hither" "thither" "yonder"] "new": ["near" "far"]] ; firstarg "hello ${words.old.(2)}"`, want: "hello yonder"},
-		{desc: "interpolate string 9", expr: `$what = "world" ; firstarg "hello $($what)"`, want: "hello world"},
+		{desc: "interpolate string 1", expr: `what = "world" ; firstarg "hello $what"`, want: "hello world"},
+		{desc: "interpolate string 2", expr: `what = "world" ; when = "now" ; firstarg "$when, hello $what"`, want: "now, hello world"},
+		{desc: "interpolate string 3", expr: `what = "world" ; when = "now" ; firstarg "${when}, hello ${what}"`, want: "now, hello world"},
+		{desc: "interpolate string 4", expr: `crazy = [far: "unknown"] ; firstarg "hello ${crazy.far}"`, want: "hello unknown"},
+		{desc: "interpolate string 5", expr: `oldWords = ["hither" "thither" "yonder"] ; firstarg "hello ${oldWords.(1)}"`, want: "hello thither"},
+		{desc: "interpolate string 6", expr: `oldWords = ["hither" "thither" "yonder"] ; firstarg "hello ${oldWords.(add 1 1)}"`, want: "hello yonder"},
+		{desc: "interpolate string 7", expr: `oldWords = ["hither" "thither" "yonder"] ; firstarg "hello ${oldWords.(add 2 | sub (sub 2 1) | sub 1)}"`, want: "hello hither"},
+		{desc: "interpolate string 8", expr: `words = ["old": ["hither" "thither" "yonder"] "new": ["near" "far"]] ; firstarg "hello ${words.old.(2)}"`, want: "hello yonder"},
+		{desc: "interpolate string 9", expr: `what = "world" ; firstarg "hello $($what)"`, want: "hello world"},
 		{desc: "interpolate string 10", expr: `firstarg "hello $([1 2 3] | len)"`, want: "hello 3"},
 		{desc: "interpolate string 11", expr: `firstarg "hello $(add (add 1 2) 3)"`, want: "hello 6"},
 		{desc: "interpolate string 12", expr: `firstarg ("$(add 2 (add 1 1)) + $([1 2 3].(1) | cat ("$("")")) = $(("$(add 2 (4))"))")`, want: "4 + 2 = 6"},
@@ -62,60 +62,71 @@ func TestInst_Eval(t *testing.T) {
 		// Multi-statements
 		{desc: "multi 1", expr: `firstarg "hello" ; firstarg "world"`, want: "world"},
 		{desc: "multi 2", expr: `list "hello" | toUpper ; firstarg "world"`, want: "world"},
-		{desc: "multi 3", expr: `$new = "this is new" ; firstarg $new`, want: "this is new"},
+		{desc: "multi 3", expr: `new = "this is new" ; firstarg $new`, want: "this is new"},
 
 		// Lists
 		{desc: "list 1", expr: `firstarg ["1" "2" "3"]`, want: []any{"1", "2", "3"}},
-		{desc: "list 2", expr: `$one = "one" ; firstarg [$one (list "two" | map { |x| toUpper $x } | head) "three"]`, want: []any{"one", "TWO", "three"}},
+		{desc: "list 2", expr: `one = "one" ; firstarg [$one (list "two" | map { |x| toUpper $x } | head) "three"]`, want: []any{"one", "TWO", "three"}},
 		{desc: "list 3", expr: `firstarg []`, want: []any{}},
-		{desc: "list 4", expr: `$x = ["a" "b" "c"] ; firstarg [$x.(2) $x.(1) $x.(0)]`, want: []any{"c", "b", "a"}},
+		{desc: "list 4", expr: `x = ["a" "b" "c"] ; firstarg [$x.(2) $x.(1) $x.(0)]`, want: []any{"c", "b", "a"}},
 
 		// Maps
 		{desc: "map 1", expr: `firstarg [one:"1" two:"2" three:"3"]`, want: map[string]any{"one": "1", "two": "2", "three": "3"}},
 		{desc: "map 2", expr: `firstarg ["one":"1" "two":"2" "three":"3"]`, want: map[string]any{"one": "1", "two": "2", "three": "3"}},
 		{desc: "map 3", expr: `
-			$one = "one" ; $n1 = "1"
+			one = "one" ; n1 = "1"
 			firstarg [
 				$one:$n1
 				(list "two" | map { |x| toUpper $x } | head):(list "2" | map { |x| toUpper $x } | head)
 				three:"3"
 			]`, want: map[string]any{"one": "1", "TWO": "2", "three": "3"}},
 		{desc: "map 4", expr: `firstarg [:]`, want: map[string]any{}},
-		{desc: "map 5", expr: `$x = ["a" "b" "c"] ; firstarg ["one":$x.(2) "two":$x.(1) "three":$x.(0)]`, want: map[string]any{"one": "c", "two": "b", "three": "a"}},
-		{desc: "map 6", expr: `$x = [a:"A" b:"B" c:"C"] ; firstarg ["one":$x.c "two":$x.b "three":$x.a]`, want: map[string]any{"one": "C", "two": "B", "three": "A"}},
+		{desc: "map 5", expr: `x = ["a" "b" "c"] ; firstarg ["one":$x.(2) "two":$x.(1) "three":$x.(0)]`, want: map[string]any{"one": "c", "two": "b", "three": "a"}},
+		{desc: "map 6", expr: `x = [a:"A" b:"B" c:"C"] ; firstarg ["one":$x.c "two":$x.b "three":$x.a]`, want: map[string]any{"one": "C", "two": "B", "three": "A"}},
 
 		// Dots
-		{desc: "dot expr 1", expr: `$x = [1 2 3] ; $x.(0)`, want: 1},
-		{desc: "dot expr 2", expr: `$x = [1 2 3] ; $x.(1)`, want: 2},
-		{desc: "dot expr 3", expr: `$x = [1 2 3] ; $x.(2)`, want: 3},
-		{desc: "dot expr 4", expr: `$x = [1 2 3] ; $x.(3)`, want: nil},
-		{desc: "dot expr 5", expr: `$x = [1 2 3] ; $x.(add 1 1)`, want: 3},
-		{desc: "dot expr 6", expr: `$x = [1 2 3] ; $x.(-1)`, want: 3},
-		{desc: "dot expr 7", expr: `$x = [1 2 3] ; $x.(-2)`, want: 2},
-		{desc: "dot expr 8", expr: `$x = [1 2 3] ; $x.(-3)`, want: 1},
-		{desc: "dot expr 9", expr: `$x = [1 2 3] ; $x.(-4)`, want: nil},
+		{desc: "dot expr 1", expr: `x = [1 2 3] ; $x.(0)`, want: 1},
+		{desc: "dot expr 2", expr: `x = [1 2 3] ; $x.(1)`, want: 2},
+		{desc: "dot expr 3", expr: `x = [1 2 3] ; $x.(2)`, want: 3},
+		{desc: "dot expr 4", expr: `x = [1 2 3] ; $x.(3)`, want: nil},
+		{desc: "dot expr 5", expr: `x = [1 2 3] ; $x.(add 1 1)`, want: 3},
+		{desc: "dot expr 6", expr: `x = [1 2 3] ; $x.(-1)`, want: 3},
+		{desc: "dot expr 7", expr: `x = [1 2 3] ; $x.(-2)`, want: 2},
+		{desc: "dot expr 8", expr: `x = [1 2 3] ; $x.(-3)`, want: 1},
+		{desc: "dot expr 9", expr: `x = [1 2 3] ; $x.(-4)`, want: nil},
 
-		{desc: "dot idents 1", expr: `$x = [alpha:"hello" bravo:"world"] ; $x.alpha`, want: "hello"},
-		{desc: "dot idents 2", expr: `$x = [alpha:"hello" bravo:"world"] ; $x.bravo`, want: "world"},
-		{desc: "dot idents 3", expr: `$x = [alpha:"hello" bravo:"world"] ; $x.charlie`, want: nil},
-		{desc: "dot idents 4", expr: `$x = [alpha:"hello" bravo:"world"] ; $x.("alpha")`, want: "hello"},
-		{desc: "dot idents 5", expr: `$x = [alpha:"hello" bravo:"world"] ; $x.("bravo")`, want: "world"},
-		{desc: "dot idents 6", expr: `$x = [alpha:"hello" bravo:"world"] ; $x.("charlie")`, want: nil},
-		{desc: "dot idents 7", expr: `$x = [MORE:"stuff"] ; $x.("more" | toUpper)`, want: "stuff"},
-		{desc: "dot idents 8", expr: `$x = [MORE:"stuff"] ; $x.(toUpper ("more"))`, want: "stuff"},
-		{desc: "dot idents 9", expr: `$x = [MORE:"stuff"] ; $x.y`, want: nil},
+		{desc: "dot idents 1", expr: `x = [alpha:"hello" bravo:"world"] ; $x.alpha`, want: "hello"},
+		{desc: "dot idents 2", expr: `x = [alpha:"hello" bravo:"world"] ; $x.bravo`, want: "world"},
+		{desc: "dot idents 3", expr: `x = [alpha:"hello" bravo:"world"] ; $x.charlie`, want: nil},
+		{desc: "dot idents 4", expr: `x = [alpha:"hello" bravo:"world"] ; $x.("alpha")`, want: "hello"},
+		{desc: "dot idents 5", expr: `x = [alpha:"hello" bravo:"world"] ; $x.("bravo")`, want: "world"},
+		{desc: "dot idents 6", expr: `x = [alpha:"hello" bravo:"world"] ; $x.("charlie")`, want: nil},
+		{desc: "dot idents 7", expr: `x = [MORE:"stuff"] ; $x.("more" | toUpper)`, want: "stuff"},
+		{desc: "dot idents 8", expr: `x = [MORE:"stuff"] ; $x.(toUpper ("more"))`, want: "stuff"},
+		{desc: "dot idents 9", expr: `x = [MORE:"stuff"] ; $x.y`, want: nil},
 
-		{desc: "dot err 1", expr: `$x = [1 2 3] ; $x.Hello`, want: nil},
-		{desc: "dot err 2", expr: `$x = [1 2 3] ; $x.("world")`, want: nil},
-		{desc: "dot err 4", expr: `$x = [a:1 b:2] ; $x.(5)`, want: nil},
-		{desc: "dot err 3", expr: `$x = [a:1 b:2] ; $x.(0)`, want: nil},
-		{desc: "dot err 5", expr: `$x = 123 ; $x.(5)`, wantAnErr: true},
-		{desc: "dot err 6", expr: `$x = 123 ; $x.Five`, wantAnErr: true},
+		{desc: "dot err 1", expr: `x = [1 2 3] ; $x.Hello`, want: nil},
+		{desc: "dot err 2", expr: `x = [1 2 3] ; $x.("world")`, want: nil},
+		{desc: "dot err 4", expr: `x = [a:1 b:2] ; $x.(5)`, want: nil},
+		{desc: "dot err 3", expr: `x = [a:1 b:2] ; $x.(0)`, want: nil},
+		{desc: "dot err 5", expr: `x = 123 ; $x.(5)`, wantAnErr: true},
+		{desc: "dot err 6", expr: `x = 123 ; $x.Five`, wantAnErr: true},
 
 		{desc: "parse comments 1", expr: parseComments1, wantObj: true, wantErr: nil},
 		{desc: "parse comments 2", expr: parseComments2, wantObj: true, wantErr: nil},
 		{desc: "parse comments 3", expr: parseComments3, wantObj: true, wantErr: nil},
 		{desc: "parse comments 4", expr: parseComments4, wantObj: true, wantErr: nil},
+
+		// Assign dots
+		{desc: "assign dot 1", expr: `x = [1 2 3] ; x.(0) = 4 ; "$x"`, want: "[4 2 3]"},
+		{desc: "assign dot 2", expr: `x = [1 2 3] ; x.(1) = 5 ; "$x"`, want: "[1 5 3]"},
+		{desc: "assign dot 3", expr: `x = [1 2 3] ; x.(-1) = 6 ; "$x"`, want: "[1 2 6]"},
+		{desc: "assign dot 4", expr: `y = [a:1 b:2] ; y.a = "hello" ; "$y"`, want: `[a:hello b:2]`},
+		{desc: "assign dot 5", expr: `y = [a:1 b:2] ; y.b = "world" ; "$y"`, want: `[a:1 b:world]`},
+		{desc: "assign dot 6", expr: `y = [a:"b" b:2] ; y.($y.a) = "world" ; "$y"`, want: `[a:b b:world]`},
+		{desc: "assign dot 7", expr: `z = [a:[1 2] b:[3 3]] ; z.a.(1) = 3 ; "$z"`, want: `[a:[1 3] b:[3 3]]`},
+		{desc: "assign dot 8", expr: `z = [[1 2] [3 4]] ; z.(1).(0) = 5 ; "$z"`, want: `[[1 2] [5 4]]`},
+		{desc: "assign dot 7", expr: `z = [[a:1 b:2] [c:3 d:4]] ; z.(1).a = 5 ; "$z"`, want: `[[a:1 b:2] [a:5 c:3 d:4]]`},
 	}
 
 	for _, tt := range tests {
@@ -148,7 +159,7 @@ func TestInst_Eval_WithSubEnv(t *testing.T) {
 
 		inst := ucl.New()
 
-		res, err := inst.Eval(ctx, strings.NewReader(`$a = "hello" ; $a`), ucl.WithSubEnv())
+		res, err := inst.Eval(ctx, strings.NewReader(`a = "hello" ; $a`), ucl.WithSubEnv())
 		assert.NoError(t, err)
 		assert.Equal(t, "hello", res)
 
@@ -167,15 +178,15 @@ func TestInst_Eval_WithSubEnv(t *testing.T) {
 		}{
 			{
 				descr: "reading vars",
-				eval1: `$a = "hello" ; hook { $a }`,
-				eval2: `$a = "world" ; hook { $a }`,
+				eval1: `a = "hello" ; hook { $a }`,
+				eval2: `a = "world" ; hook { $a }`,
 				want1: "hello",
 				want2: "world",
 			},
 			{
 				descr: "modifying vars",
-				eval1: `$a = "hello" ; hook { $a = "new value" ; $a }`,
-				eval2: `$a = "world" ; hook { $a }`,
+				eval1: `a = "hello" ; hook { a = "new value" ; $a }`,
+				eval2: `a = "world" ; hook { $a }`,
 				want1: "new value",
 				want2: "world",
 			},
@@ -195,8 +206,8 @@ func TestInst_Eval_WithSubEnv(t *testing.T) {
 			},
 			{
 				descr: "exporting procs 2",
-				eval1: `$a = "hello" ; export say_hello { $a = "world"; $a } ; hook { say_hello }`,
-				eval2: `$a = "other" ; hook { say_hello }`,
+				eval1: `a = "hello" ; export say_hello { a = "world"; $a } ; hook { say_hello }`,
+				eval2: `a = "other" ; hook { say_hello }`,
 				want1: "world",
 				want2: "world",
 			},
diff --git a/ucl/objs.go b/ucl/objs.go
index 981f7ab..2ecde0f 100644
--- a/ucl/objs.go
+++ b/ucl/objs.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"reflect"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -35,9 +36,13 @@ type ModListable interface {
 
 	// Insert adds a new item to the list. idx can be a positive
 	// number from 0 to len(), in which case the object will be inserted
-	// at that position.  If idx is negative, then the item will be inserted
+	// at that position, shifting all other elements to the right.
+	// If idx is negative, then the item will be inserted
 	// at that position from the right.
 	Insert(idx int, obj Object) error
+
+	// SetIndex replaces the item at index position idx with obj.
+	SetIndex(idx int, obj Object) error
 }
 
 type Hashable interface {
@@ -46,6 +51,11 @@ type Hashable interface {
 	Each(func(k string, v Object) error) error
 }
 
+type ModHashable interface {
+	Hashable
+	SetValue(k string, val Object) error
+}
+
 type ListObject []Object
 
 func NewListObject() *ListObject {
@@ -80,6 +90,11 @@ func (s *ListObject) Index(i int) Object {
 	return (*s)[i]
 }
 
+func (s *ListObject) SetIndex(i int, toVal Object) error {
+	(*s)[i] = toVal
+	return nil
+}
+
 type StringListObject []string
 
 func (ss StringListObject) String() string {
@@ -117,9 +132,17 @@ func (s HashObject) String() string {
 		return "[:]"
 	}
 
+	// Return the keys in sorted order
+	keys := make([]string, 0, len(s))
+	for k := range s {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+
 	sb := strings.Builder{}
 	sb.WriteString("[")
-	for k, v := range s {
+	for _, k := range keys {
+		v := s[k]
 		if sb.Len() != 1 {
 			sb.WriteString(" ")
 		}
@@ -152,6 +175,11 @@ func (s HashObject) Each(fn func(k string, v Object) error) error {
 	return nil
 }
 
+func (s HashObject) SetValue(k string, val Object) error {
+	s[k] = val
+	return nil
+}
+
 type StringObject string
 
 func (s StringObject) String() string {
diff --git a/ucl/userbuiltin_test.go b/ucl/userbuiltin_test.go
index 58bf5ab..5e3fe30 100644
--- a/ucl/userbuiltin_test.go
+++ b/ucl/userbuiltin_test.go
@@ -124,7 +124,7 @@ func TestInst_SetBuiltin(t *testing.T) {
 			want  string
 		}{
 			{descr: "pass via args", expr: `join (add2 "left" "right")`, want: "left:right"},
-			{descr: "pass via vars", expr: `$x = (add2 "blue" "green") ; join $x`, want: "blue:green"},
+			{descr: "pass via vars", expr: `x = (add2 "blue" "green") ; join $x`, want: "blue:green"},
 		}
 
 		for _, tt := range tests {