diff --git a/README.md b/README.md
index e66f01bf84..1a74e07e7b 100644
--- a/README.md
+++ b/README.md
@@ -170,7 +170,7 @@ https://github.com/vlang/ui
 
 ```v
 fn main() {
-        for i := 0; i < 3; i++ {
+        for i in 0..3 {
                 println('Hello from V.js')
         }
 }
diff --git a/doc/docs.md b/doc/docs.md
index 19679417a2..0c133b8282 100644
--- a/doc/docs.md
+++ b/doc/docs.md
@@ -641,7 +641,7 @@ so `register()` can change the user object. The same works with non-receiver arg
 
 ```v
 fn multiply_by_2(arr mut []int) {
-    for i := 0; i < arr.len; i++ {
+    for i in 0..arr.len {
         arr[i] *= 2
     }
 }
diff --git a/examples/cli.v b/examples/cli.v
index 62f637a823..93a1c4ce4d 100644
--- a/examples/cli.v
+++ b/examples/cli.v
@@ -41,7 +41,7 @@ fn greet_func(cmd cli.Command) {
 	language := cmd.flags.get_string('language') or { panic('failed to get \'language\' flag: $err') }
 	times := cmd.flags.get_int('times') or { panic('failed to get \'times\' flag: $err') }
 
-	for i := 0; i < times; i++ {
+	for i in 0..times {
 		match language {
 			'english' { println('Hello World') }
 			'german' { println('Hallo Welt') }
diff --git a/examples/fibonacci.v b/examples/fibonacci.v
index 5976fef4cf..8861080acc 100644
--- a/examples/fibonacci.v
+++ b/examples/fibonacci.v
@@ -25,7 +25,7 @@ fn main() {
 	mut b := u64(0)
 	mut c := u64(1)
 
-	for i := 0; i < stop; i++ {
+	for i in 0..stop {
 		// Set a and b to the next term
 		a = b
 		b = c
diff --git a/examples/game_of_life/modules/automaton/automaton.v b/examples/game_of_life/modules/automaton/automaton.v
index b31fa33a76..d31a1381cb 100644
--- a/examples/game_of_life/modules/automaton/automaton.v
+++ b/examples/game_of_life/modules/automaton/automaton.v
@@ -48,8 +48,8 @@ fn new_automaton(f [][]int) Automaton {
 	}
 	field     := &A2D{ maxx: maxx maxy: maxy data: &int( calloc( sizeof(int) * maxy * maxx ) ) }
 	new_field := &A2D{ maxx: maxx maxy: maxy data: &int( calloc( sizeof(int) * maxy * maxx ) ) }
-	for y := 0; y < field.maxy; y++ {
-		for x := 0; x < field.maxx; x++ {
+	for y in 0..field.maxy {
+		for x in 0..field.maxx {
 			field.set( x, y, f[y][x] )
 		}
 	}
diff --git a/examples/hello_v_js.v b/examples/hello_v_js.v
index 16c9536ed2..41ab9c1bf7 100644
--- a/examples/hello_v_js.v
+++ b/examples/hello_v_js.v
@@ -1,5 +1,5 @@
 fn main() {
-        for i := 0; i < 3; i++ {
+        for i in 0..3 {
                 println('Hello from V.js')
         }
 }
diff --git a/examples/nbody.v b/examples/nbody.v
index 5fa23a457b..7ec43f1874 100644
--- a/examples/nbody.v
+++ b/examples/nbody.v
@@ -33,7 +33,7 @@ pub mut:
 }
 
 fn advance(sys mut System, dt f64) {
-    for i := 0; i < N - 1; i++ {
+    for i in 0..N - 1 {
         mut _vx := sys.v[i].x
         mut _vy := sys.v[i].y
         mut _vz := sys.v[i].z
@@ -61,7 +61,7 @@ fn advance(sys mut System, dt f64) {
         sys.v[i].z = _vz
     }
 
-    for i := 0; i < N; i++ {
+    for i in 0..N {
         sys.s[i].x += dt * sys.v[i].x
         sys.s[i].y += dt * sys.v[i].y
         sys.s[i].z += dt * sys.v[i].z
@@ -73,7 +73,7 @@ fn offsetmomentum(sys mut System) {
     mut py := f64(0)
     mut pz := f64(0)
 
-    for i := 0; i < N; i++ {
+    for i in 0..N {
         px += sys.v[i].x * sys.v[i].m
         py += sys.v[i].y * sys.v[i].m
         pz += sys.v[i].z * sys.v[i].m
@@ -85,7 +85,7 @@ fn offsetmomentum(sys mut System) {
 
 fn energy(sys System) f64 {
     mut e := f64(0)
-    for i := 0; i < N; i++ {
+    for i in 0..N {
         e += 0.5 * sys.v[i].m * (sys.v[i].x * sys.v[i].x + sys.v[i].y * sys.v[i].y + sys.v[i].z * sys.v[i].z)
         for j := i + 1; j < N; j++ {
             dx := sys.s[i].x - sys.s[j].x
@@ -124,7 +124,7 @@ sys := &System {arr_momentum(), arr_position()}
 offsetmomentum(mut sys)
 
 println('${energy(sys):.9f}')  //-0.169075164
-for i := 0; i < 50000000; i++ {
+for i in 0..50000000 {
     advance(mut sys, 0.01)
 }
 println('${energy(sys):.9f}') //-0.169059907
diff --git a/examples/news_fetcher.v b/examples/news_fetcher.v
index e2fb26d43e..f15e87b68e 100644
--- a/examples/news_fetcher.v
+++ b/examples/news_fetcher.v
@@ -58,7 +58,7 @@ fn main() {
 	if ids.len > 10 {
 		// ids = ids[:10]
 		mut tmp := [0].repeat(10)
-		for i := 0; i < 10; i++ {
+		for i in 0..10 {
 			tmp[i] = ids[i]
 		}
 		ids = tmp
@@ -69,7 +69,7 @@ fn main() {
 		wg: sync.new_waitgroup()
 	}
 	fetcher.wg.add(ids.len)
-	for i := 0; i < nr_threads; i++ {
+	for i in 0..nr_threads {
 		go fetcher.fetch()
 	}
 	fetcher.wg.wait()
diff --git a/examples/path_tracing.v b/examples/path_tracing.v
index 5e753efa78..1ad3044fe1 100644
--- a/examples/path_tracing.v
+++ b/examples/path_tracing.v
@@ -409,7 +409,7 @@ fn ray_trace(w int, h int, samps int, file_name string, scene_id int) Image {
 	// OpenMP injection point! #pragma omp parallel for schedule(dynamic, 1) shared(c)
 	for y:=0; y < h; y++ {
 		eprint("\rRendering (${samps * 4} spp) ${(100.0 * f64(y)) / (f64(h) - 1.0):5.2f}%")
-		for x := 0; x < w; x++ {
+		for x in 0..w {
 			
 			i := (h - y - 1) * w + x
 			mut ivec := &image.data[i]
@@ -417,7 +417,7 @@ fn ray_trace(w int, h int, samps int, file_name string, scene_id int) Image {
 			for sy := 0; sy < 2; sy ++ {
 				for sx := 0; sx < 2; sx ++ {
 					r = Vec{0,0,0}
-					for s := 0; s < samps; s++ {
+					for s in 0..samps {
 						r1 := v_2 * rand_f64()
 						dx := if r1 < v_1 { math.sqrt(r1) - v_1 } else { v_1 - math.sqrt(v_2 - r1) }
 						
diff --git a/examples/spectral.v b/examples/spectral.v
index cd95f7d5de..4056fae01b 100644
--- a/examples/spectral.v
+++ b/examples/spectral.v
@@ -18,9 +18,9 @@ fn evala(i, j int) int {
 }
 
 fn times(v mut []f64, u []f64) {
-	for i := 0; i < v.len; i++ {
+	for i in 0..v.len {
 		mut a := f64(0)
-		for j := 0; j < u.len; j++ {
+		for j in 0..u.len {
 			a += u[j] / f64(evala(i, j))
 		}
 		v[i] = a
@@ -28,9 +28,9 @@ fn times(v mut []f64, u []f64) {
 }
 
 fn times_trans(v mut []f64, u []f64) {
-	for i := 0; i < v.len; i++ {
+	for i in 0..v.len {
 		mut a := f64(0)
-		for j := 0; j < u.len; j++ {
+		for j in 0..u.len {
 			a += u[j] / f64(evala(j, i))
 		}
 		v[i] = a
@@ -54,13 +54,13 @@ fn main() {
 	}
 	mut u := [f64(1.0)].repeat(n)
 	mut v := [f64(1.0)].repeat(n)
-	for i := 0; i < 10; i++ {
+	for i in 0..10 {
 		a_times_transp(mut v, u)
 		a_times_transp(mut u, v)
 	}
 	mut vbv := f64(0)
 	mut vv := f64(0)
-	for i := 0; i < n; i++ {
+	for i in 0..n {
 		vbv += u[i] * v[i]
 		vv += v[i] * v[i]
 	}
diff --git a/examples/tetris/tetris.v b/examples/tetris/tetris.v
index 0c19f532ac..3e05f7549e 100644
--- a/examples/tetris/tetris.v
+++ b/examples/tetris/tetris.v
@@ -175,7 +175,7 @@ fn (g mut Game) init_game() {
 	g.generate_tetro()
 	g.field = [] // TODO: g.field = [][]int
 	// Generate the field, fill it with 0's, add -1's on each edge
-	for i := 0; i < FieldHeight + 2; i++ {
+	for i in 0..FieldHeight + 2 {
 		mut row := [0].repeat(FieldWidth + 2)
 		row[0] = - 1
 		row[FieldWidth + 1] = - 1
@@ -183,7 +183,7 @@ fn (g mut Game) init_game() {
 	}
 	mut first_row := g.field[0]
 	mut last_row := g.field[FieldHeight + 1]
-	for j := 0; j < FieldWidth + 2; j++ {
+	for j in 0..FieldWidth + 2 {
 		first_row[j] = - 1
 		last_row[j] = - 1
 	}
@@ -238,7 +238,7 @@ fn (g mut Game) move_tetro() {
 
 fn (g mut Game) move_right(dx int) bool {
 	// Reached left/right edge or another tetro?
-	for i := 0; i < TetroSize; i++ {
+	for i in 0..TetroSize {
 		tetro := g.tetro[i]
 		y := tetro.y + g.pos_y
 		x := tetro.x + g.pos_x + dx
@@ -293,7 +293,7 @@ fn (g mut Game) get_tetro() {
 
 // TODO mut
 fn (g &Game) drop_tetro() {
-	for i := 0; i < TetroSize; i++ {
+	for i in 0..TetroSize {
 		tetro := g.tetro[i]
 		x := tetro.x + g.pos_x
 		y := tetro.y + g.pos_y
@@ -305,7 +305,7 @@ fn (g &Game) drop_tetro() {
 }
 
 fn (g &Game) draw_tetro() {
-	for i := 0; i < TetroSize; i++ {
+	for i in 0..TetroSize {
 		tetro := g.tetro[i]
 		g.draw_block(g.pos_y + tetro.y, g.pos_x + tetro.x, g.tetro_idx + 1)
 	}
diff --git a/examples/vcasino/VCasino.v b/examples/vcasino/VCasino.v
index c5f5c9fac7..8b2d8b817d 100644
--- a/examples/vcasino/VCasino.v
+++ b/examples/vcasino/VCasino.v
@@ -21,7 +21,7 @@ fn display_help() {
 
 fn option_parser() bool {
     help := Options{'--help', '-h'}
-    for i := 0; i < os.args.len; i++ {
+    for i in 0..os.args.len {
         if os.args[i]== help.long_opt || os.args[i]== help.short_opt {
             display_help()
             return true
@@ -31,7 +31,7 @@ fn option_parser() bool {
 }
 
 fn str_is_nbr(s string) bool {
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
         if !s[i].is_digit() {
             return false
         }
diff --git a/vlib/bitfield/bitfield.v b/vlib/bitfield/bitfield.v
index 4a2b57e7dd..2b5a154bd0 100644
--- a/vlib/bitfield/bitfield.v
+++ b/vlib/bitfield/bitfield.v
@@ -91,7 +91,7 @@ pub fn from_bytes(input []byte) BitField {
 
 pub fn from_string(input string) BitField {
 	mut output := new(input.len)
-	for i := 0; i < input.len; i++ {
+	for i in 0..input.len {
 		if input[i] != 48 {
 			output.setbit(i)
 		}
@@ -104,7 +104,7 @@ pub fn from_string(input string) BitField {
 
 pub fn (input BitField) string() string {
 	mut output := ''
-	for i := 0; i < input.size; i++ {
+	for i in 0..input.size {
 		if input.getbit(i) == 1 {
 			output = output + '1'
 		}
@@ -157,7 +157,7 @@ pub fn (instance mut BitField) clearbit(bitnr int) {
 // setall() sets all bits in the array to 1
 
 pub fn (instance mut BitField) setall() {
-	for i := 0; i < bitnslots(instance.size); i++ {
+	for i in 0..bitnslots(instance.size) {
 		instance.field[i] = u32(-1)
 	}
 	cleartail(mut instance)
@@ -166,7 +166,7 @@ pub fn (instance mut BitField) setall() {
 // clearall() clears (sets to zero) all bits in the array
 
 pub fn (instance mut BitField) clearall() {
-	for i := 0; i < bitnslots(instance.size); i++ {
+	for i in 0..bitnslots(instance.size) {
 		instance.field[i] = u32(0)
 	}
 }
@@ -251,7 +251,7 @@ pub fn join(input1 BitField, input2 BitField) BitField {
 	output_size := input1.size + input2.size
 	mut output := new(output_size)
 	// copy the first input to output as is
-	for i := 0; i < bitnslots(input1.size); i++ {
+	for i in 0..bitnslots(input1.size) {
 		output.field[i] = input1.field[i]
 	}
 
@@ -259,7 +259,7 @@ pub fn join(input1 BitField, input2 BitField) BitField {
 	offset_bit := input1.size % SLOT_SIZE
 	offset_slot := input1.size / SLOT_SIZE
 
-	for i := 0; i < bitnslots(input2.size); i++ {
+	for i in 0..bitnslots(input2.size) {
 		output.field[i + offset_slot] |=
 		    u32(input2.field[i] << u32(offset_bit))
 	}
@@ -278,12 +278,12 @@ pub fn join(input1 BitField, input2 BitField) BitField {
 	 * If offset_bit is zero, no additional copies needed.
 	 */
 	if (output_size - 1) % SLOT_SIZE < (input2.size - 1) % SLOT_SIZE {
-		for i := 0; i < bitnslots(input2.size); i++ {
+		for i in 0..bitnslots(input2.size) {
 			output.field[i + offset_slot + 1] |=
 			    u32(input2.field[i] >> u32(SLOT_SIZE - offset_bit))
 		}
 	} else if (output_size - 1) % SLOT_SIZE > (input2.size - 1) % SLOT_SIZE {
-		for i := 0; i < bitnslots(input2.size) - 1; i++ {
+		for i in 0..bitnslots(input2.size) - 1 {
 			output.field[i + offset_slot + 1] |=
 			    u32(input2.field[i] >> u32(SLOT_SIZE - offset_bit))
 		}
@@ -331,7 +331,7 @@ pub fn clone(input BitField) BitField {
 
 pub fn cmp(input1 BitField, input2 BitField) bool {
 	if input1.size != input2.size {return false}
-	for i := 0; i < bitnslots(input1.size); i++ {
+	for i in 0..bitnslots(input1.size) {
 		if input1.field[i] != input2.field[i] {return false}
 	}
 	return true
@@ -344,14 +344,14 @@ pub fn (instance BitField) popcount() int {
 	bitnslots := bitnslots(size)
 	tail := size % SLOT_SIZE
 	mut count := 0
-	for i := 0; i < bitnslots - 1; i++ {
-		for j := 0; j < SLOT_SIZE; j++ {
+	for i in 0..bitnslots - 1 {
+		for j in 0..SLOT_SIZE {
 			if u32(instance.field[i] >> u32(j)) & u32(1) == u32(1) {
 				count++
 			}
 		}
 	}
-	for j := 0; j < tail; j++ {
+	for j in 0..tail {
 		if u32(instance.field[bitnslots - 1] >> u32(j)) & u32(1) == u32(1) {
 			count++
 		}
@@ -412,7 +412,7 @@ pub fn (input BitField) slice(_start int, _end int) BitField {
 
 	if output_slots > 1 {
 		if start_offset != 0 {
-			for i := 0; i < output_slots - 1; i++ {
+			for i in 0..output_slots - 1 {
 				output.field[i] =
 				    u32(input.field[start_slot + i] >> u32(start_offset))
 				output.field[i] = output.field[i] |
@@ -421,7 +421,7 @@ pub fn (input BitField) slice(_start int, _end int) BitField {
 			}
 		}
 		else {
-			for i := 0; i < output_slots - 1; i++ {
+			for i in 0..output_slots - 1 {
 				output.field[i] =
 				    u32(input.field[start_slot + i])
 			}
@@ -465,14 +465,14 @@ pub fn (instance BitField) reverse() BitField {
 	bitnslots := bitnslots(size)
 	mut output := new(size)
 	for i:= 0; i < (bitnslots - 1); i++ {
-		for j := 0; j < SLOT_SIZE; j++ {
+		for j in 0..SLOT_SIZE {
 			if u32(instance.field[i] >> u32(j)) & u32(1) == u32(1) {
 				bitset(mut output, size - i * SLOT_SIZE - j - 1)
 			}
 		}
 	}
 	bits_in_last_input_slot := (size - 1) % SLOT_SIZE + 1
-	for j := 0; j < bits_in_last_input_slot; j++ {
+	for j in 0..bits_in_last_input_slot {
 		if u32(instance.field[bitnslots - 1] >> u32(j)) & u32(1) == u32(1) {
 			bitset(mut output, bits_in_last_input_slot - j - 1)
 		}
diff --git a/vlib/bitfield/bitfield_test.v b/vlib/bitfield/bitfield_test.v
index 6977b1d38c..8d2279bf9d 100644
--- a/vlib/bitfield/bitfield_test.v
+++ b/vlib/bitfield/bitfield_test.v
@@ -49,7 +49,7 @@ fn test_clone_cmp() {
 	rand.seed(time.now().unix)
 	len := 80
 	mut input := bitfield.new(len)
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if rand.next(2) == 1 {
 			input.setbit(i)
 		}
@@ -63,7 +63,7 @@ fn test_slice_join() {
 	rand.seed(time.now().unix)
 	len := 80
 	mut input := bitfield.new(len)
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if rand.next(2) == 1 {
 			input.setbit(i)
 		}
@@ -87,7 +87,7 @@ fn test_popcount() {
 	len := 80
 	mut count0 := 0
 	mut input := bitfield.new(len)
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if rand.next(2) == 1 {
 			input.setbit(i)
 			count0++
@@ -103,7 +103,7 @@ fn test_hamming() {
 	mut count := 0
 	mut input1 := bitfield.new(len)
 	mut input2 := bitfield.new(len)
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		match rand.next(4) {
 			0, 1 {
 				input1.setbit(i)
@@ -129,7 +129,7 @@ fn test_bf_from_bytes() {
 	input := [byte(0xF0), byte(0x0F), byte(0xF0), byte(0xFF)]
 	output := bitfield.from_bytes(input)
 	mut result := 1
-	for i := 0; i < input.len * 8; i++ {
+	for i in 0..input.len * 8 {
 		if (input[i / 8] >> (i % 8)) & 1 != output.getbit(i) {
 			result = 0
 		}
@@ -141,7 +141,7 @@ fn test_bf_from_string() {
 	rand.seed(time.now().unix)
 	len := 80
 	mut input := ''
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if rand.next(2) == 1 {
 			input = input + '1'
 		}
@@ -151,7 +151,7 @@ fn test_bf_from_string() {
 	}
 	output := bitfield.from_string(input)
 	mut result := 1
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if input[i] != output.getbit(i) + 48 {
 			result = 0
 		}
@@ -163,13 +163,13 @@ fn test_bf_bf2str() {
 	rand.seed(time.now().unix)
 	len := 80
 	mut input := bitfield.new(len)
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if rand.next(2) == 1 {
 			input.setbit(i)
 		}
 	}
 	mut check := ''
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if input.getbit(i) == 1 {
 			check = check + '1'
 		}
@@ -179,7 +179,7 @@ fn test_bf_bf2str() {
 	}
 	output := input.string()
 	mut result := 1
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if check[i] != output[i] {
 			result = 0
 		}
@@ -193,7 +193,7 @@ fn test_bf_setall() {
 	mut input := bitfield.new(len)
 	input.setall()
 	mut result := 1
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if input.getbit(i) != 1 {
 			result = 0
 		}
@@ -205,14 +205,14 @@ fn test_bf_clearall() {
 		rand.seed(time.now().unix)
 	len := 80
 	mut input := bitfield.new(len)
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if rand.next(2) == 1 {
 			input.setbit(i)
 		}
 	}
 	input.clearall()
 	mut result := 1
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if input.getbit(i) != 0 {
 			result = 0
 		}
@@ -224,7 +224,7 @@ fn test_bf_reverse() {
 	rand.seed(time.now().unix)
 	len := 80
 	mut input := bitfield.new(len)
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if rand.next(2) == 1 {
 			input.setbit(i)
 		}
@@ -232,7 +232,7 @@ fn test_bf_reverse() {
 	check := bitfield.clone(input)
 	output := input.reverse()
 	mut result := 1
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		if output.getbit(i) != check.getbit(len - i - 1) {
 			result = 0
 		}
@@ -244,7 +244,7 @@ fn test_bf_resize() {
 	rand.seed(time.now().unix)
 	len := 80
 	mut input := bitfield.new(rand.next(len) + 1)
-	for i := 0; i < 100; i++ {
+	for i in 0..100 {
 		input.resize(rand.next(len) + 1)
 		input.setbit(input.getsize() - 1)
 	}
@@ -263,12 +263,12 @@ fn test_bf_pos() {
 	len := 80
 	mut result := 1
 	for i := 1; i < len; i++ {	// needle size
-		for j := 0; j < len - i; j++ {	// needle position in the haystack
+		for j in 0..len - i {	// needle position in the haystack
 			// create the needle
 			mut needle := bitfield.new(i)
 
 			// fill the needle with random values
-			for k := 0; k < i; k++ {
+			for k in 0..i {
 				if rand.next(2) == 1 {
 					needle.setbit(k)
 				}
diff --git a/vlib/builtin/array.v b/vlib/builtin/array.v
index 5962596d64..a5e583e7e3 100644
--- a/vlib/builtin/array.v
+++ b/vlib/builtin/array.v
@@ -98,7 +98,7 @@ pub fn (a array) repeat(nr_repeats int) array {
 		element_size: a.element_size
 		data: calloc(size)
 	}
-	for i := 0; i < nr_repeats; i++ {
+	for i in 0..nr_repeats {
 		C.memcpy(arr.data + i * a.len * a.element_size, a.data, a.len * a.element_size)
 	}
 	return arr
@@ -335,7 +335,7 @@ pub fn (a array) reverse() array {
 		element_size: a.element_size
 		data: calloc(a.cap * a.element_size)
 	}
-	for i := 0; i < a.len; i++ {
+	for i in 0..a.len {
 		C.memcpy(arr.data + i * arr.element_size, &a[a.len - 1 - i], arr.element_size)
 	}
 	return arr
@@ -355,7 +355,7 @@ pub fn (a array) free() {
 pub fn (a []string) str() string {
 	mut sb := strings.new_builder(a.len * 3)
 	sb.write('[')
-	for i := 0; i < a.len; i++ {
+	for i in 0..a.len {
 		val := a[i]
 		sb.write('"')
 		sb.write(val)
@@ -373,7 +373,7 @@ pub fn (a []string) str() string {
 pub fn (a []bool) str() string {
 	mut sb := strings.new_builder(a.len * 3)
 	sb.write('[')
-	for i := 0; i < a.len; i++ {
+	for i in 0..a.len {
 		val := a[i]
 		if val {
 			sb.write('true')
@@ -394,7 +394,7 @@ pub fn (a []bool) str() string {
 pub fn (b []byte) hex() string {
 	mut hex := malloc(b.len * 2 + 1)
 	mut ptr := &hex[0]
-	for i := 0; i < b.len; i++ {
+	for i in 0..b.len {
 		// QTODO
 		ptr += C.sprintf(ptr, '%02x', b[i])
 	}
@@ -435,7 +435,7 @@ pub fn (a mut []int) sort() {
 // []string.index returns the index of the first element equal to the given value,
 // or -1 if the value is not found in the array.
 pub fn (a []string) index(v string) int {
-	for i := 0; i < a.len; i++ {
+	for i in 0..a.len {
 		if a[i] == v {
 			return i
 		}
@@ -446,7 +446,7 @@ pub fn (a []string) index(v string) int {
 // []int.index returns the index of the first element equal to the given value,
 // or -1 if the value is not found in the array.
 pub fn (a []int) index(v int) int {
-	for i := 0; i < a.len; i++ {
+	for i in 0..a.len {
 		if a[i] == v {
 			return i
 		}
@@ -457,7 +457,7 @@ pub fn (a []int) index(v int) int {
 // []byte.index returns the index of the first element equal to the given value,
 // or -1 if the value is not found in the array.
 pub fn (a []byte) index(v byte) int {
-	for i := 0; i < a.len; i++ {
+	for i in 0..a.len {
 		if a[i] == v {
 			return i
 		}
@@ -469,7 +469,7 @@ pub fn (a []byte) index(v byte) int {
 // or -1 if the value is not found in the array.
 // TODO is `char` type yet in the language?
 pub fn (a []char) index(v char) int {
-	for i := 0; i < a.len; i++ {
+	for i in 0..a.len {
 		if a[i] == v {
 			return i
 		}
@@ -480,13 +480,11 @@ pub fn (a []char) index(v char) int {
 // []int.reduce executes a given reducer function on each element of the array,
 // resulting in a single output value.
 pub fn (a []int) reduce(iter fn(accum, curr int)int, accum_start int) int {
-	mut _accum := 0
-	/*
-	_accum = accum_start
-	for i := 0; i < a.len; i++ {
-		_accum = iter(_accum, a[i])
+	mut _accum := accum_start
+	for i in a {
+		_accum = iter(_accum, i)
 	}
-	*/
+	
 	return _accum
 }
 
@@ -497,7 +495,7 @@ fn array_eq<T>(a1, a2 []T) bool {
 	if a1.len != a2.len {
 		return false
 	}
-	for i := 0; i < a1.len; i++ {
+	for i in 0..a1.len {
 		if a1[i] != a2[i] {
 			return false
 		}
@@ -528,7 +526,7 @@ pub fn (a1 []string) eq(a2 []string) bool {
 	if a1.len != a2.len {
 		return false
 	}
-	for i := 0; i < a1.len; i++ {
+	for i in 0..a1.len {
 		if a1[i] != a2[i] {
 			return false
 		}
diff --git a/vlib/builtin/array_test.v b/vlib/builtin/array_test.v
index 3195b1c62c..a851a7a9df 100644
--- a/vlib/builtin/array_test.v
+++ b/vlib/builtin/array_test.v
@@ -62,7 +62,7 @@ fn test_short() {
 
 fn test_large() {
 	mut a := [0].repeat(0)
-	for i := 0; i < 10000; i++ {
+	for i in 0..10000 {
 		a << i
 	}
 	assert a.len == 10000
@@ -311,7 +311,7 @@ fn test_clone() {
 
 fn test_doubling() {
 	mut nums := [1, 2, 3, 4, 5]
-	for i := 0; i < nums.len; i++ {
+	for i in 0..nums.len {
 		nums[i] *= 2
 	}
 	assert nums.str() == '[2, 4, 6, 8, 10]'
@@ -562,7 +562,7 @@ fn test_push_many_self() {
     actual_arr << actual_arr
     expected_arr := [1, 2, 3, 4, 1, 2, 3, 4]
     assert actual_arr.len == expected_arr.len
-    for i := 0; i < actual_arr.len; i++ {
+    for i in 0..actual_arr.len {
         assert actual_arr[i] == expected_arr[i]
     }
 }
diff --git a/vlib/builtin/bare/array_bare.v b/vlib/builtin/bare/array_bare.v
index e80ec8a53a..a2f8c0c181 100644
--- a/vlib/builtin/bare/array_bare.v
+++ b/vlib/builtin/bare/array_bare.v
@@ -47,7 +47,7 @@ pub fn (a array) repeat(nr_repeats int) array {
 		element_size: a.element_size
 		data: malloc(nr_repeats * a.len * a.element_size)
 	}
-	for i := 0; i < nr_repeats; i++ {
+	for i in 0..nr_repeats {
 		mem_copy(arr.data + i * a.len * a.element_size, a.data, a.len * a.element_size)
 	}
 	return arr
diff --git a/vlib/builtin/bare/string_bare.v b/vlib/builtin/bare/string_bare.v
index 1c6eb423d8..3b4d2e69e9 100644
--- a/vlib/builtin/bare/string_bare.v
+++ b/vlib/builtin/bare/string_bare.v
@@ -28,10 +28,10 @@ fn (s string) add(a string) string {
 		len: new_len
 		str: malloc(new_len + 1)
 	}
-	for j := 0; j < s.len; j++ {
+	for j in 0..s.len {
 		res[j] = s[j]
 	}
-	for j := 0; j < a.len; j++ {
+	for j in 0..a.len {
 		res[s.len + j] = a[j]
 	}
 	res[new_len] = `\0`// V strings are not null terminated, but just in case
diff --git a/vlib/builtin/int.v b/vlib/builtin/int.v
index ae20bb4985..f9adcf7827 100644
--- a/vlib/builtin/int.v
+++ b/vlib/builtin/int.v
@@ -186,7 +186,7 @@ pub fn (c rune) str() string {
 		len: len
 		str: malloc(len + 1)
 	}
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		str.str[i] = int(c)>>8 * (3 - i) & 0xff
 	}
 	str[len] = `\0`
@@ -210,7 +210,7 @@ pub fn (c byte) is_capital() bool {
 pub fn (b []byte) clone() []byte {
 	mut res := [byte(0)].repeat(b.len)
 	//mut res := make([]byte, {repeat:b.len})
-	for i := 0; i < b.len; i++ {
+	for i in 0..b.len {
 		res[i] = b[i]
 	}
 	return res
diff --git a/vlib/builtin/js/array.v b/vlib/builtin/js/array.v
index 705f7103c0..53d0fc2a95 100644
--- a/vlib/builtin/js/array.v
+++ b/vlib/builtin/js/array.v
@@ -109,7 +109,7 @@ pub fn (a array) free() {
 pub fn (a []string) str() string {
 	mut sb := strings.new_builder(a.len * 3)
 	sb.write('[')
-	for i := 0; i < a.len; i++ {
+	for i in 0..a.len {
 		val := a[i]
 		sb.write('"')
 		sb.write(val)
diff --git a/vlib/builtin/js/int.v b/vlib/builtin/js/int.v
index 1c1c7d4fec..f1affe00da 100644
--- a/vlib/builtin/js/int.v
+++ b/vlib/builtin/js/int.v
@@ -83,7 +83,7 @@ pub fn (c byte) is_capital() bool {
 
 pub fn (b []byte) clone() []byte {
 	mut res := [byte(0)].repeat(b.len)
-	for i := 0; i < b.len; i++ {
+	for i in 0..b.len {
 		res[i] = b[i]
 	}
 	return res
diff --git a/vlib/builtin/map_test.v b/vlib/builtin/map_test.v
index f232448ea9..c6003cfc70 100644
--- a/vlib/builtin/map_test.v
+++ b/vlib/builtin/map_test.v
@@ -74,7 +74,7 @@ fn test_large_map() {
 	//ticks := time.ticks()
 	mut nums := map[string]int
 	N := 30 * 1000
-	for i := 0; i < N; i++ {
+	for i in 0..N {
 	        key := i.str()
 	        nums[key] = i
 	}
diff --git a/vlib/builtin/sorted_map.v b/vlib/builtin/sorted_map.v
index d2e9fad020..f1dd745ee4 100644
--- a/vlib/builtin/sorted_map.v
+++ b/vlib/builtin/sorted_map.v
@@ -309,7 +309,7 @@ fn (n mut mapnode) merge(idx int) {
 	sibling := &mapnode(n.children[idx + 1])
 	child.keys[mid_index] = n.keys[idx]
 	child.values[mid_index] = n.values[idx]
-	for i := 0; i < sibling.size; i++ {
+	for i in 0..sibling.size {
 		child.keys[i + degree] = sibling.keys[i]
 		child.values[i + degree] = sibling.values[i]
 	}
@@ -413,4 +413,4 @@ pub fn (m SortedMap) print() {
 // 	}
 // 	sb.writeln('}')
 // 	return sb.str()
-// }
\ No newline at end of file
+// }
diff --git a/vlib/builtin/string.v b/vlib/builtin/string.v
index c84ba6ea16..b1e8232476 100644
--- a/vlib/builtin/string.v
+++ b/vlib/builtin/string.v
@@ -109,7 +109,7 @@ pub fn (a string) clone() string {
 		len: a.len
 		str: malloc(a.len + 1)
 	}
-	for i := 0; i < a.len; i++ {
+	for i in 0..a.len {
 		b[i] = a[i]
 	}
 	b[a.len] = `\0`
@@ -168,7 +168,7 @@ pub fn (s string) replace(rep, with string) string {
 	for i := 0; i < s.len; i++ {
 		// Reached the location of rep, replace it with "with"
 		if i == cur_idx {
-			for j := 0; j < with.len; j++ {
+			for j in 0..with.len {
 				b[b_i] = with[j]
 				b_i++
 			}
@@ -266,7 +266,7 @@ val_idx:rep_i}
 		if i == cur_idx.idx {
 			rep := vals[cur_idx.val_idx]
 			with := vals[cur_idx.val_idx + 1]
-			for j := 0; j < with.len; j++ {
+			for j in 0..with.len {
 				b[b_i] = with[j]
 				b_i++
 			}
@@ -339,7 +339,7 @@ fn (s string) eq(a string) bool {
 	if s.len != a.len {
 		return false
 	}
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
 		if s[i] != a[i] {
 			return false
 		}
@@ -354,7 +354,7 @@ fn (s string) ne(a string) bool {
 
 // s < a
 fn (s string) lt(a string) bool {
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
 		if i >= a.len || s[i] > a[i] {
 			return false
 		}
@@ -390,10 +390,10 @@ fn (s string) add(a string) string {
 		len: new_len
 		str: malloc(new_len + 1)
 	}
-	for j := 0; j < s.len; j++ {
+	for j in 0..s.len {
 		res[j] = s[j]
 	}
-	for j := 0; j < a.len; j++ {
+	for j in 0..a.len {
 		res[s.len + j] = a[j]
 	}
 	res[new_len] = `\0` // V strings are not null terminated, but just in case
@@ -528,7 +528,7 @@ pub fn (s string) substr(start, end int) string {
 		len: len
 		str: malloc(len + 1)
 	}
-	for i := 0; i < len; i++ {
+	for i in 0..len {
 		res.str[i] = s.str[start + i]
 	}
 	res.str[len] = `\0`
@@ -595,7 +595,7 @@ fn (s string) index_kmp(p string) int {
 		prefix[i] = j
 	}
 	j = 0
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
 		for p[j] != s[i] && j > 0 {
 			j = prefix[j - 1]
 		}
@@ -665,7 +665,7 @@ pub fn (s string) index_after(p string, start int) int {
 }
 
 pub fn (s string) index_byte(c byte) int {
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
 		if s[i] == c {
 			return i
 		}
@@ -714,7 +714,7 @@ pub fn (s string) starts_with(p string) bool {
 	if p.len > s.len {
 		return false
 	}
-	for i := 0; i < p.len; i++ {
+	for i in 0..p.len {
 		if s[i] != p[i] {
 			return false
 		}
@@ -726,7 +726,7 @@ pub fn (s string) ends_with(p string) bool {
 	if p.len > s.len {
 		return false
 	}
-	for i := 0; i < p.len; i++ {
+	for i in 0..p.len {
 		if p[i] != s[s.len - p.len + i] {
 			return false
 		}
@@ -737,7 +737,7 @@ pub fn (s string) ends_with(p string) bool {
 // TODO only works with ASCII
 pub fn (s string) to_lower() string {
 	mut b := malloc(s.len + 1)
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
 		b[i] = C.tolower(s.str[i])
 	}
 	return tos(b, s.len)
@@ -745,7 +745,7 @@ pub fn (s string) to_lower() string {
 
 pub fn (s string) to_upper() string {
 	mut b := malloc(s.len + 1)
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
 		b[i] = C.toupper(s.str[i])
 	}
 	return tos(b, s.len)
@@ -807,7 +807,7 @@ fn (ar []int) contains(val int) bool {
 /*
 pub fn (a []string) to_c() voidptr {
 	mut res := malloc(sizeof(byteptr) * a.len)
-	for i := 0; i < a.len; i++ {
+	for i in 0..a.len {
 		val := a[i]
 		res[i] = val.str
 	}
@@ -1177,14 +1177,14 @@ pub fn (a []string) join(del string) string {
 	mut idx := 0
 	// Go thru every string and copy its every char one by one
 	for i, val in a {
-		for j := 0; j < val.len; j++ {
+		for j in 0..val.len {
 			c := val[j]
 			res.str[idx] = val.str[j]
 			idx++
 		}
 		// Add del if it's not last
 		if i != a.len - 1 {
-			for k := 0; k < del.len; k++ {
+			for k in 0..del.len {
 				res.str[idx] = del.str[k]
 				idx++
 			}
diff --git a/vlib/cli/command.v b/vlib/cli/command.v
index fb8420105b..63fc36f3e4 100644
--- a/vlib/cli/command.v
+++ b/vlib/cli/command.v
@@ -43,7 +43,7 @@ pub fn (cmd mut Command) parse(args []string) {
 	cmd.add_default_commands()
 
 	cmd.args = args[1..]
-	for i := 0; i < cmd.commands.len; i++ {
+	for i in 0..cmd.commands.len {
 		cmd.commands[i].parent = cmd
 	}
 
@@ -75,7 +75,7 @@ fn (cmd mut Command) parse_flags() {
 			break
 		}
 		mut found := false
-		for i := 0; i < cmd.flags.len; i++ {
+		for i in 0..cmd.flags.len {
 			mut flag := &cmd.flags[i]
 			if flag.matches(cmd.args) {
 				found = true
@@ -102,9 +102,9 @@ fn (cmd &Command) parse_commands() {
 	cmd.check_help_flag()
 	cmd.check_version_flag()
 
-	for i := 0; i < cmd.args.len; i++ {
+	for i in 0..cmd.args.len {
 		arg := cmd.args[i]
-		for j := 0; j < cmd.commands.len; j++ {
+		for j in 0..cmd.commands.len {
 			mut command := cmd.commands[j]
 			if command.name == arg {
 				for flag in global_flags {
diff --git a/vlib/cli/command_test.v b/vlib/cli/command_test.v
index 66c4895a68..b0b7884f44 100644
--- a/vlib/cli/command_test.v
+++ b/vlib/cli/command_test.v
@@ -178,7 +178,7 @@ fn compare_arrays(array0 []string, array1 []string) bool {
 	if array0.len != array1.len {
 		return false
 	}
-	for i := 0; i < array0.len; i++ {
+	for i in 0..array0.len {
 		if array0[i] != array1[i] {
 			return false
 		}
diff --git a/vlib/clipboard/clipboard_linux.v b/vlib/clipboard/clipboard_linux.v
index d20a1416d3..decf50578e 100644
--- a/vlib/clipboard/clipboard_linux.v
+++ b/vlib/clipboard/clipboard_linux.v
@@ -361,7 +361,7 @@ fn (cb &Clipboard) pick_target(prop Property) Atom {
 		//This is higher than the maximum priority.
 		mut priority := math.max_i32
 
-		for i := 0; i < prop.nitems; i++ {
+		for i in 0..prop.nitems {
 			//See if this data type is allowed and of higher priority (closer to zero)
 			//than the present one.
 
diff --git a/vlib/crypto/aes/block_generic.v b/vlib/crypto/aes/block_generic.v
index 4729400229..ca3bb39abe 100644
--- a/vlib/crypto/aes/block_generic.v
+++ b/vlib/crypto/aes/block_generic.v
@@ -63,7 +63,7 @@ fn encrypt_block_generic(xk []u32, dst, src []byte) {
 	mut t1 := u32(0)
 	mut t2 := u32(0)
 	mut t3 := u32(0)
-	for r := 0; r < nr; r++ {
+	for r in 0..nr {
 		t0 = xk[k+0] ^ te0[byte(s0>>24)] ^ te1[byte(s1>>16)] ^ te2[byte(s2>>8)] ^ u32(te3[byte(s3)])
 		t1 = xk[k+1] ^ te0[byte(s1>>24)] ^ te1[byte(s2>>16)] ^ te2[byte(s3>>8)] ^ u32(te3[byte(s0)])
 		t2 = xk[k+2] ^ te0[byte(s2>>24)] ^ te1[byte(s3>>16)] ^ te2[byte(s0>>8)] ^ u32(te3[byte(s1)])
@@ -115,7 +115,7 @@ fn decrypt_block_generic(xk []u32, dst, src []byte) {
 	mut t1 := u32(0)
 	mut t2 := u32(0)
 	mut t3 := u32(0)
-	for r := 0; r < nr; r++ {
+	for r in 0..nr {
 		t0 = xk[k+0] ^ td0[byte(s0>>24)] ^ td1[byte(s3>>16)] ^ td2[byte(s2>>8)] ^ u32(td3[byte(s1)])
 		t1 = xk[k+1] ^ td0[byte(s1>>24)] ^ td1[byte(s0>>16)] ^ td2[byte(s3>>8)] ^ u32(td3[byte(s2)])
 		t2 = xk[k+2] ^ td0[byte(s2>>24)] ^ td1[byte(s1>>16)] ^ td2[byte(s0>>8)] ^ u32(td3[byte(s3)])
@@ -189,7 +189,7 @@ fn expand_key_generic(key []byte, enc mut []u32, dec mut []u32) {
 	n := enc.len
 	for i = 0; i < n; i += 4 {
 		ei := n - i - 4
-		for j := 0; j < 4; j++ {
+		for j in 0..4 {
 			mut x := enc[ei+j]
 			if i > 0 && i+4 < n {
 				x = td0[s_box0[x>>24]] ^ td1[s_box0[x>>16&0xff]] ^ td2[s_box0[x>>8&0xff]] ^ td3[s_box0[x&u32(0xff)]]
diff --git a/vlib/crypto/cipher/xor_generic.v b/vlib/crypto/cipher/xor_generic.v
index 5ab797a2b3..d93336b7b9 100644
--- a/vlib/crypto/cipher/xor_generic.v
+++ b/vlib/crypto/cipher/xor_generic.v
@@ -24,7 +24,7 @@ pub fn xor_bytes(dst mut []byte, a, b []byte) int {
 
 // n needs to be smaller or equal than the length of a and b.
 pub fn safe_xor_bytes(dst mut []byte, a, b []byte, n int) {
-	for i := 0; i < n; i++ {
+	for i in 0..n {
 		dst[i] = a[i] ^ b[i]
 	}
 }
diff --git a/vlib/crypto/rc4/rc4.v b/vlib/crypto/rc4/rc4.v
index 985ab48934..5ff4f90c53 100644
--- a/vlib/crypto/rc4/rc4.v
+++ b/vlib/crypto/rc4/rc4.v
@@ -32,11 +32,11 @@ pub fn new_cipher(key []byte) ?Cipher {
 	mut c := Cipher{
 		s: [u32(0)].repeat(256)
 	}
-	for i := 0; i < 256; i++ {
+	for i in 0..256 {
 		c.s[i] = u32(i)
 	}
 	mut j := byte(0)
-	for i := 0; i < 256; i++ {
+	for i in 0..256 {
 		j += byte(c.s[i]) + key[i%key.len]
 		tmp := c.s[i]
 		c.s[i] = c.s[j]
diff --git a/vlib/crypto/sha1/sha1block_generic.v b/vlib/crypto/sha1/sha1block_generic.v
index fad3eef5aa..02b7e06fdb 100644
--- a/vlib/crypto/sha1/sha1block_generic.v
+++ b/vlib/crypto/sha1/sha1block_generic.v
@@ -28,7 +28,7 @@ fn block_generic(dig mut Digest, p_ []byte) {
 	for p.len >= chunk {
 		// Can interlace the computation of w with the
 		// rounds below if needed for speed.
-		for i := 0; i < 16; i++ {
+		for i in 0..16 {
 			j := i * 4
 			w[i] = u32(p[j]<<24) | u32(p[j+1]<<16) | u32(p[j+2]<<8) | u32(p[j+3])
 		}
diff --git a/vlib/crypto/sha256/sha256block_generic.v b/vlib/crypto/sha256/sha256block_generic.v
index e6807d04be..12328b240c 100644
--- a/vlib/crypto/sha256/sha256block_generic.v
+++ b/vlib/crypto/sha256/sha256block_generic.v
@@ -97,7 +97,7 @@ fn block_generic(dig mut Digest, p_ []byte) {
 	for p.len >= chunk {
 		// Can interlace the computation of w with the
 		// rounds below if needed for speed.
-		for i := 0; i < 16; i++ {
+		for i in 0..16 {
 			j := i * 4
 			w[i] = u32(p[j]<<24) | u32(p[j+1]<<16) | u32(p[j+2]<<8) | u32(p[j+3])
 		}
@@ -118,7 +118,7 @@ fn block_generic(dig mut Digest, p_ []byte) {
 		mut g := h6
 		mut h := h7
 
-		for i := 0; i < 64; i++ {
+		for i in 0..64 {
 			t1 := h + ((bits.rotate_left_32(e, -6)) ^ (bits.rotate_left_32(e, -11)) ^ (bits.rotate_left_32(e, -25))) + ((e & f) ^ (~e & g)) + u32(_k[i]) + w[i]
 			t2 := ((bits.rotate_left_32(a, -2)) ^ (bits.rotate_left_32(a, -13)) ^ (bits.rotate_left_32(a, -22))) + ((a & b) ^ (a & c) ^ (b & c))
 
diff --git a/vlib/crypto/sha512/sha512block_generic.v b/vlib/crypto/sha512/sha512block_generic.v
index 77fee2ba77..b28cc9e222 100644
--- a/vlib/crypto/sha512/sha512block_generic.v
+++ b/vlib/crypto/sha512/sha512block_generic.v
@@ -105,7 +105,7 @@ fn block_generic(dig mut Digest, p_ []byte) {
 	mut h6 := dig.h[6]
 	mut h7 := dig.h[7]
 	for p.len >= Chunk {
-		for i := 0; i < 16; i++ {
+		for i in 0..16 {
 			j := i * 8
 			w[i] = (u64(p[j])<<56) | (u64(p[j + 1])<<48) | (u64(p[j + 2])<<40) | (u64(p[j + 3])<<32) | (u64(p[j + 4])<<24) | (u64(p[j + 5])<<16) | (u64(p[j + 6])<<8) | u64(p[j + 7])
 		}
@@ -124,7 +124,7 @@ fn block_generic(dig mut Digest, p_ []byte) {
 		mut f := h5
 		mut g := h6
 		mut h := h7
-		for i := 0; i < 80; i++ {
+		for i in 0..80 {
 			t1 := h + (bits.rotate_left_64(e, -14) ^ bits.rotate_left_64(e, -18) ^ bits.rotate_left_64(e, -41)) + ((e & f) ^ (~e & g)) + _k[i] + w[i]
 			t2 := (bits.rotate_left_64(a, -28) ^ bits.rotate_left_64(a, -34) ^ bits.rotate_left_64(a, -39)) + ((a & b) ^ (a & c) ^ (b & c))
 			h = g
diff --git a/vlib/encoding/base64/base64_memory_test.v b/vlib/encoding/base64/base64_memory_test.v
index c33fba9b3d..161eee8c9d 100644
--- a/vlib/encoding/base64/base64_memory_test.v
+++ b/vlib/encoding/base64/base64_memory_test.v
@@ -14,14 +14,14 @@ fn test_long_encoding(){
 	mut s := 0
 
 	ebuffer := malloc( s_encoded.len )
-	for i := 0; i < repeats; i++ {
+	for i in 0..repeats {
 		resultsize := base64.encode_in_buffer(s_original, ebuffer)
 		s += resultsize
 		assert resultsize == s_encoded.len
 	}
 
 	dbuffer := malloc( s_decoded.len )
-	for i := 0; i < repeats; i++ {
+	for i in 0..repeats {
 		resultsize := base64.decode_in_buffer(s_encoded, dbuffer)
 		s += resultsize
 		assert resultsize == s_decoded.len
diff --git a/vlib/freetype/freetype.v b/vlib/freetype/freetype.v
index 2306a58bff..d4431006a8 100644
--- a/vlib/freetype/freetype.v
+++ b/vlib/freetype/freetype.v
@@ -226,7 +226,7 @@ pub fn new_context(cfg gg.Cfg) &FreeType {
 	// Gen texture
 	// Load first 128 characters of ASCII set
 	mut chars := []Character
-	for c := 0; c < 128; c++ {
+	for c in 0..128 {
 		ch := ft_load_char(face, i64(c))
 		// s := utf32_to_str(uint(0x043f))
 		// s := 'п'
@@ -309,7 +309,7 @@ fn (ctx mut FreeType) private_draw_text(_x, _y int, utext ustring, cfg gx.TextCf
 	gl.bind_vao(ctx.vao)
 	// Iterate through all characters
 	// utext := text.ustring()
-	for i := 0; i < utext.len; i++ {
+	for i in 0..utext.len {
 		_rune := utext.at(i)
 		// println('$i => $_rune')
 		mut ch := Character{}
@@ -325,7 +325,7 @@ fn (ctx mut FreeType) private_draw_text(_x, _y int, utext ustring, cfg gx.TextCf
 		}
 		else if _rune.len > 1 {
 			// TODO O(1) use map
-			for j := 0; j < ctx.utf_runes.len; j++ {
+			for j in 0..ctx.utf_runes.len {
 				rune_j := ctx.utf_runes[j]
 				if rune_j==_rune {
 					ch = ctx.utf_chars[j]
@@ -406,7 +406,7 @@ pub fn (ctx mut FreeType) text_size(s string) (int, int) {
 	mut maxy := u32(0)
 	mut _rune := ''
 	mut ch := Character{}
-	for i := 0; i < utext.len; i++ {
+	for i in 0..utext.len {
 		_rune = utext.at(i)
 		ch = Character{}		
 		mut found := false
@@ -421,7 +421,7 @@ pub fn (ctx mut FreeType) text_size(s string) (int, int) {
 		}
 		else if _rune.len > 1 {
 			// TODO O(1) use map
-			for j := 0; j < ctx.utf_runes.len; j++ {
+			for j in 0..ctx.utf_runes.len {
 				rune_j := ctx.utf_runes[j]
 				if rune_j==_rune {
 					ch = ctx.utf_chars[j]
diff --git a/vlib/glm/glm.v b/vlib/glm/glm.v
index fa21901113..ba6c18a6d8 100644
--- a/vlib/glm/glm.v
+++ b/vlib/glm/glm.v
@@ -59,11 +59,11 @@ pub fn (v Vec2) str() string {
 
 pub fn (m Mat4) str() string {
 	mut s := '[ '
-	for i := 0; i < 4; i++ {
+	for i in 0..4 {
 		if i != 0 {
 			s += '  '
 		}
-		for j := 0; j < 4; j++ {
+		for j in 0..4 {
 			val := m.data[i * 4 + j]
 			s += '${val:.2f} '
 		}
diff --git a/vlib/hash/crc32/crc32.v b/vlib/hash/crc32/crc32.v
index e75b8f7e37..7c116f2abe 100644
--- a/vlib/hash/crc32/crc32.v
+++ b/vlib/hash/crc32/crc32.v
@@ -24,9 +24,9 @@ mut:
 }
 
 fn(c mut Crc32) generate_table(poly int) {
-	for i := 0; i < 256; i++ {
+	for i in 0..256 {
 		mut crc := u32(i)
-		for j := 0; j < 8; j++ {
+		for j in 0..8 {
 			if crc & u32(1) == u32(1) {
 				crc = (crc >> 1) ^ u32(poly)
 			} else {
@@ -39,7 +39,7 @@ fn(c mut Crc32) generate_table(poly int) {
 
 fn(c &Crc32) sum32(b []byte) u32 {
 	mut crc := ~u32(0)
-	for i := 0; i < b.len; i++ {
+	for i in 0..b.len {
 		crc = c.table[byte(crc)^b[i]] ^ u32(crc >> u32(8))
 	}
 	return ~crc
diff --git a/vlib/hash/fnv1a/fnv1a.v b/vlib/hash/fnv1a/fnv1a.v
index 2ef6f423ca..24c35b2690 100644
--- a/vlib/hash/fnv1a/fnv1a.v
+++ b/vlib/hash/fnv1a/fnv1a.v
@@ -10,7 +10,7 @@ const (
 [inline]
 pub fn sum32_string(data string) u32 {
 	mut hash := fnv32_offset_basis
-	for i := 0; i < data.len; i++ {
+	for i in 0..data.len {
 		hash = (hash ^ u32(data[i])) * fnv32_prime
 	}
 	return hash
@@ -19,7 +19,7 @@ pub fn sum32_string(data string) u32 {
 [inline]
 pub fn sum32(data []byte) u32 {
 	mut hash := fnv32_offset_basis
-	for i := 0; i < data.len; i++ {
+	for i in 0..data.len {
 		hash = (hash ^ u32(data[i])) * fnv32_prime
 	}
 	return hash
@@ -28,7 +28,7 @@ pub fn sum32(data []byte) u32 {
 [inline]
 pub fn sum64_string(data string) u64 {
 	mut hash := fnv64_offset_basis
-	for i := 0; i < data.len; i++ {
+	for i in 0..data.len {
 		hash = (hash ^ u64(data[i])) * fnv64_prime
 	}
 	return hash
@@ -37,7 +37,7 @@ pub fn sum64_string(data string) u64 {
 [inline]
 pub fn sum64(data []byte) u64 {
 	mut hash := fnv64_offset_basis
-	for i := 0; i < data.len; i++ {
+	for i in 0..data.len {
 		hash = (hash ^ u64(data[i])) * fnv64_prime
 	}
 	return hash
diff --git a/vlib/math/stats/stats.v b/vlib/math/stats/stats.v
index bde6853e49..8affafd1fa 100644
--- a/vlib/math/stats/stats.v
+++ b/vlib/math/stats/stats.v
@@ -119,7 +119,7 @@ pub fn mode(arr []f64) f64 {
 		freqs<<freq(arr,v)
 	}
 	mut max := 0
-	for i := 0; i < freqs.len; i++ {
+	for i in 0..freqs.len {
 		if freqs[i] > freqs[max] {
 			max = i
 		}
diff --git a/vlib/mysql/result.v b/vlib/mysql/result.v
index 7ee4280c72..589205c08a 100644
--- a/vlib/mysql/result.v
+++ b/vlib/mysql/result.v
@@ -45,7 +45,7 @@ pub fn (r Result) rows() []Row {
 	nr_cols := r.num_fields()
 	for rr := r.fetch_row(); rr; rr = r.fetch_row() {
 		mut row := Row{}
-		for i := 0; i < nr_cols; i++ {
+		for i in 0..nr_cols {
 			if rr[i] == 0 {
 				row.vals << ''
 			} else {
@@ -61,7 +61,7 @@ pub fn (r Result) fetch_fields() []Field {
 	mut fields := []Field
 	nr_cols := r.num_fields()
 	orig_fields := mysql_fetch_fields(r.result)
-	for i := 0; i < nr_cols; i++ {
+	for i in 0..nr_cols {
 		fields << Field{
 			name: string(orig_fields[i].name)
 			org_name: string(orig_fields[i].org_name)
diff --git a/vlib/net/ftp/ftp.v b/vlib/net/ftp/ftp.v
index d6a1efa806..3c4b34cc47 100644
--- a/vlib/net/ftp/ftp.v
+++ b/vlib/net/ftp/ftp.v
@@ -47,7 +47,7 @@ fn (dtp DTP) read() []byte {
 		buf, len := dtp.sock.recv(1024)
 		if len == 0 { break }
 
-		for i := 0; i < len; i++ {
+		for i in 0..len {
 			data << buf[i]
 		}
 		unsafe { free(buf) }
diff --git a/vlib/net/socket.v b/vlib/net/socket.v
index 20ac95316d..cf0ef5830d 100644
--- a/vlib/net/socket.v
+++ b/vlib/net/socket.v
@@ -329,7 +329,7 @@ pub fn (s Socket) read_line() string {
 		}
 		buf[n] = `\0`
 		mut eol_idx := -1
-		for i := 0; i < n; i++ {
+		for i in 0..n {
 			if int(buf[i]) == `\n` {
 				eol_idx = i
 				// Ensure that tos_clone(buf) later,
diff --git a/vlib/net/urllib/urllib.v b/vlib/net/urllib/urllib.v
index e35e3cd453..81f8a9e12c 100644
--- a/vlib/net/urllib/urllib.v
+++ b/vlib/net/urllib/urllib.v
@@ -242,7 +242,7 @@ fn escape(s string, mode EncodingMode) string {
 	mut space_count := 0
 	mut hex_count := 0
 	mut c := byte(0)
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
 		c = s[i]
 		if should_escape(c, mode) {
 			if c == ` ` && mode == .encode_query_component {
@@ -267,7 +267,7 @@ fn escape(s string, mode EncodingMode) string {
 	}
 	if hex_count == 0 {
 		copy(t, s.bytes())
-		for i := 0; i < s.len; i++ {
+		for i in 0..s.len {
 			if s[i] == ` ` {
 				t[i] = `+`
 			}
@@ -276,7 +276,7 @@ fn escape(s string, mode EncodingMode) string {
 	}
 	upperhex := '0123456789ABCDEF'
 	mut j := 0
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
 		c1 := s[i]
 		if c1 == ` ` && mode == .encode_query_component {
 			t[j] = `+`
@@ -382,7 +382,7 @@ fn (u &Userinfo) string() string {
 // (scheme must be [a-zA-Z][a-zA-Z0-9+-.]*)
 // If so, return [scheme, path]; else return ['', rawurl]
 fn split_by_scheme(rawurl string) ?[]string {
-	for i := 0; i < rawurl.len; i++ {
+	for i in 0..rawurl.len {
 		c := rawurl[i]
 		if (`a` <= c && c <= `z`) || (`A` <= c && c <= `Z`) {
 			// do nothing
@@ -692,7 +692,7 @@ fn (u &URL) escaped_path() string {
 // valid_encoded_path reports whether s is a valid encoded path.
 // It must not contain any bytes that require escaping during path encoding.
 fn valid_encoded_path(s string) bool {
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
 		// RFC 3986, Appendix A.
 		// pchar = unreserved / pct-encoded / sub-delims / ':' / '@'.
 		// should_escape is not quite compliant with the RFC,
@@ -1097,7 +1097,7 @@ pub fn valid_userinfo(s string) bool {
 
 // string_contains_ctl_byte reports whether s contains any ASCII control character.
 fn string_contains_ctl_byte(s string) bool {
-	for i := 0; i < s.len; i++ {
+	for i in 0..s.len {
 		b := s[i]
 		if b < ` ` || b == 0x7f {
 			return true
diff --git a/vlib/os/os_windows.v b/vlib/os/os_windows.v
index e0efb66767..9a834e637b 100644
--- a/vlib/os/os_windows.v
+++ b/vlib/os/os_windows.v
@@ -82,7 +82,7 @@ mut:
 
 fn init_os_args_wide(argc int, argv &byteptr) []string {
 	mut args := []string
-	for i := 0; i < argc; i++ {
+	for i in 0..argc {
 		args << string_from_wide(&u16(argv[i]))
 	}
 	return args
diff --git a/vlib/pg/pg.v b/vlib/pg/pg.v
index af59aaa911..97b64fe272 100644
--- a/vlib/pg/pg.v
+++ b/vlib/pg/pg.v
@@ -50,9 +50,9 @@ fn res_to_rows(res voidptr) []pg.Row {
 	nr_rows := C.PQntuples(res)
 	nr_cols := C.PQnfields(res)
 	mut rows := []pg.Row
-	for i := 0; i < nr_rows; i++ {
+	for i in 0..nr_rows {
 		mut row := Row{}
-		for j := 0; j < nr_cols; j++ {
+		for j in 0..nr_cols {
 			val := C.PQgetvalue(res, i, j)
 			row.vals << string(val)
 		}
@@ -124,7 +124,7 @@ pub fn (db DB) exec_one(query string) ?pg.Row {
 //
 pub fn (db DB) exec_param_many(query string, params []string) []pg.Row {
 	mut param_vals := &byteptr( malloc( params.len * sizeof(byteptr) ) )
-	for i := 0; i < params.len; i++ {
+	for i in 0..params.len {
 		param_vals[i] = params[i].str
 	}
 	res := C.PQexecParams(db.conn, query.str, params.len, 0, param_vals, 0, 0, 0)
diff --git a/vlib/sdl/examples/tvintris/tvintris.v b/vlib/sdl/examples/tvintris/tvintris.v
index 2ed96427a8..ec404d4dd9 100644
--- a/vlib/sdl/examples/tvintris/tvintris.v
+++ b/vlib/sdl/examples/tvintris/tvintris.v
@@ -257,11 +257,11 @@ fn (sdlc mut SdlContext) set_sdl_context(w int, h int, title string) {
 		C.Mix_VolumeMusic(sdlc.actx.volume)
 	}
 	njoy := C.SDL_NumJoysticks()
-	for i := 0; i < njoy; i++ {
+	for i in 0..njoy {
 		C.SDL_JoystickOpen(i)
 		jn := tos_clone(sdl.joystick_name_for_index(i))
 		println('JOY NAME $jn')
-		for j := 0; j < NJOYMAX; j++ {
+		for j in 0..NJOYMAX {
 			if sdlc.jnames[j] == jn {
 				println('FOUND JOYSTICK $j $jn ID=$i')
 				sdlc.jids[j] = i
@@ -534,7 +534,7 @@ fn (g mut Game) init_game() {
 	g.generate_tetro()
 	g.field = []
 	// Generate the field, fill it with 0's, add -1's on each edge
-	for i := 0; i < FieldHeight + 2; i++ {
+	for i in 0..FieldHeight + 2 {
 		mut row := [0].repeat(FieldWidth + 2)
 		row[0] = - 1
 		row[FieldWidth + 1] = - 1
@@ -542,7 +542,7 @@ fn (g mut Game) init_game() {
 	}
 	mut first_row := g.field[0]
 	mut last_row := g.field[FieldHeight + 1]
-	for j := 0; j < FieldWidth + 2; j++ {
+	for j in 0..FieldWidth + 2 {
 		first_row[j] = - 1
 		last_row[j] = - 1
 	}
@@ -626,7 +626,7 @@ fn (g mut Game) move_tetro() {
 
 fn (g mut Game) move_right(dx int) bool {
 	// Reached left/right edge or another tetro?
-	for i := 0; i < TetroSize; i++ {
+	for i in 0..TetroSize {
 		tetro := g.tetro[i]
 		y := tetro.y + g.pos_y
 		x := tetro.x + g.pos_x + dx
@@ -693,7 +693,7 @@ fn (g mut Game) get_tetro() {
 }
 
 fn (g &Game) drop_tetro() {
-	for i := 0; i < TetroSize; i++ {
+	for i in 0..TetroSize {
 		tetro := g.tetro[i]
 		x := tetro.x + g.pos_x
 		y := tetro.y + g.pos_y
@@ -705,7 +705,7 @@ fn (g &Game) drop_tetro() {
 }
 
 fn (g &Game) draw_tetro() {
-	for i := 0; i < TetroSize; i++ {
+	for i in 0..TetroSize {
 		tetro := g.tetro[i]
 		g.draw_block(g.pos_y + tetro.y, g.pos_x + tetro.x, g.tetro_idx + 1)
 	}
diff --git a/vlib/strings/similarity.v b/vlib/strings/similarity.v
index 93f1d58369..76b2c08ec8 100644
--- a/vlib/strings/similarity.v
+++ b/vlib/strings/similarity.v
@@ -51,13 +51,13 @@ pub fn dice_coefficient(s1, s2 string) f32 {
 	a := if s1.len > s2.len { s1 } else { s2 }
 	b := if a == s1 { s2 } else { s1 }
 	mut first_bigrams := map[string]int
-	for i := 0; i < a.len - 1; i++ {
+	for i in 0..a.len - 1 {
 		bigram := a[i..i + 2]
 		q := if bigram in first_bigrams { first_bigrams[bigram] + 1 } else { 1 }
 		first_bigrams[bigram] = q
 	}
 	mut intersection_size := 0
-	for i := 0; i < b.len - 1; i++ {
+	for i in 0..b.len - 1 {
 		bigram := b[i..i + 2]
 		count := if bigram in first_bigrams { first_bigrams[bigram] } else { 0 }
 		if count > 0 {
diff --git a/vlib/time/time_test.v b/vlib/time/time_test.v
index 39c4edae24..ca9b7e4153 100644
--- a/vlib/time/time_test.v
+++ b/vlib/time/time_test.v
@@ -106,7 +106,7 @@ fn test_smonth() {
 }
 
 fn test_day_of_week() {
-	for i := 0; i < 7; i++ {
+	for i in 0..7 {
 		day_of_week := i + 1
 		// 2 Dec 2019 is Monday
 		t := time.Time{
diff --git a/vlib/v/gen/cgen_test.v b/vlib/v/gen/cgen_test.v
index 0d526f00b5..65df7b3d2f 100644
--- a/vlib/v/gen/cgen_test.v
+++ b/vlib/v/gen/cgen_test.v
@@ -16,7 +16,7 @@ fn test_c_files() {
 	vroot := filepath.dir(vexe)
 	term_ok := term.ok_message('OK')
 	term_fail := term.fail_message('FAIL')
-	for i in 1 .. nr_tests + 1 {
+	for i in 1..(nr_tests + 1) {
 		path := '$vroot/vlib/v/gen/tests/${i}.vv'
 		mut ctext := os.read_file('$vroot/vlib/v/gen/tests/${i}.c') or {
 			panic(err)
diff --git a/vlib/vweb/vweb.v b/vlib/vweb/vweb.v
index be4f5680aa..f1e10de6f7 100644
--- a/vlib/vweb/vweb.v
+++ b/vlib/vweb/vweb.v
@@ -192,7 +192,7 @@ fn handle_conn<T>(conn net.Socket, app mut T) {
 	mut len := 0
 	mut body_len := 0
 	//for line in lines[1..] {
-	for j := 0; j < 100; j++ {
+	for j in 0..100 {
 		//println(j)
 		line := conn.read_line()
 		sline := strip(line)