diff --git a/cmd/tools/preludes/tests_assertions.v b/cmd/tools/preludes/tests_assertions.v
index ec901e96a7..f6769ec4ff 100644
--- a/cmd/tools/preludes/tests_assertions.v
+++ b/cmd/tools/preludes/tests_assertions.v
@@ -11,7 +11,7 @@ import term
 // / since it is done in normal V code, instead of in embedded C ...
 // //////////////////////////////////////////////////////////////////
 fn cb_assertion_failed(filename string, line int, sourceline string, funcname string) {
-	color_on := term.can_show_color_on_stderr()
+	// color_on := term.can_show_color_on_stderr()
 	use_relative_paths := match os.getenv('VERROR_PATHS') {
 		'absolute'{
 			false
diff --git a/cmd/v/v.v b/cmd/v/v.v
index d8567c9227..7ee0187532 100644
--- a/cmd/v/v.v
+++ b/cmd/v/v.v
@@ -125,6 +125,9 @@ fn parse_args(args []string) (&pref.Preferences, string) {
 			'-live' {
 				res.is_live = true
 			}
+			'-repl' {
+				res.is_repl = true
+			}
 			'-sharedlive' {
 				res.is_live = true
 				res.is_shared = true
diff --git a/vlib/builtin/builtin_windows.c.v b/vlib/builtin/builtin_windows.c.v
index 5cf489241c..1a774616b7 100644
--- a/vlib/builtin/builtin_windows.c.v
+++ b/vlib/builtin/builtin_windows.c.v
@@ -92,7 +92,8 @@ $if msvc {
 	handle := C.GetCurrentProcess()
 	defer { C.SymCleanup(handle) }
 
-	options := C.SymSetOptions(SYMOPT_DEBUG | SYMOPT_LOAD_LINES | SYMOPT_UNDNAME)
+	C.SymSetOptions(SYMOPT_DEBUG | SYMOPT_LOAD_LINES | SYMOPT_UNDNAME)
+
 	syminitok := C.SymInitialize( handle, 0, 1)
 	if syminitok != 1 {
 		println('Failed getting process: Aborting backtrace.\n')
diff --git a/vlib/builtin/string.v b/vlib/builtin/string.v
index 720aa22f33..6aa21d6220 100644
--- a/vlib/builtin/string.v
+++ b/vlib/builtin/string.v
@@ -1223,7 +1223,6 @@ pub fn (a []string) join(del string) string {
 	// Go thru every string and copy its every char one by one
 	for i, val in a {
 		for j in 0..val.len {
-			c := val[j]
 			res.str[idx] = val.str[j]
 			idx++
 		}
diff --git a/vlib/v/ast/scope.v b/vlib/v/ast/scope.v
index 1aca6c7346..34d9f3cddf 100644
--- a/vlib/v/ast/scope.v
+++ b/vlib/v/ast/scope.v
@@ -4,6 +4,7 @@
 module ast
 
 import v.table
+import v.token
 
 pub struct Scope {
 mut:
@@ -11,9 +12,15 @@ mut:
 	children  []&Scope
 	start_pos int
 	end_pos   int
+	unused_vars map[string]UnusedVar
 	objects   map[string]ScopeObject
 }
 
+pub struct UnusedVar {
+	name string
+	pos token.Position
+}
+
 pub fn new_scope(parent &Scope, start_pos int) &Scope {
 	return &ast.Scope{
 		parent: parent
@@ -107,6 +114,30 @@ pub fn (s mut Scope) register(name string, obj ScopeObject) {
 	s.objects[name] = obj
 }
 
+pub fn (s mut Scope) register_unused_var(name string, pos token.Position) {
+	s.unused_vars[name] = UnusedVar{name, pos}
+}
+
+pub fn (s mut Scope) remove_unused_var(name string) {
+	mut sc := s
+	for !isnil(sc) {
+		sc.unused_vars.delete(name)
+		sc = sc.parent
+	}
+}
+
+pub fn (s mut Scope) unused_vars() []UnusedVar {
+	ret := []UnusedVar
+	for _, v in s.unused_vars {
+		ret << v
+	}
+	return ret
+}
+
+pub fn (s mut Scope) clear_unused_vars() {
+	s.unused_vars = map[string]UnusedVar
+}
+
 pub fn (s &Scope) outermost() &Scope {
 	mut sc := s
 	for !isnil(sc.parent) {
diff --git a/vlib/v/builder/cc.v b/vlib/v/builder/cc.v
index f504b6aae5..fef727be91 100644
--- a/vlib/v/builder/cc.v
+++ b/vlib/v/builder/cc.v
@@ -174,7 +174,7 @@ fn (v mut Builder) cc() {
 	is_cc_clang := v.pref.ccompiler.contains('clang') || guessed_compiler == 'clang'
 	is_cc_tcc  := v.pref.ccompiler.contains('tcc') || guessed_compiler == 'tcc'
 	is_cc_gcc  := v.pref.ccompiler.contains('gcc') || guessed_compiler == 'gcc'
-	is_cc_msvc := v.pref.ccompiler.contains('msvc') || guessed_compiler == 'msvc'
+	// is_cc_msvc := v.pref.ccompiler.contains('msvc') || guessed_compiler == 'msvc'
 	//
 	if is_cc_clang {
 		if debug_mode {
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 6491370da4..f5ae37c9d4 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1515,7 +1515,7 @@ pub fn (c mut Checker) match_expr(node mut ast.MatchExpr) table.Type {
 
 		if !has_else {
 			mut used_values_count := 0
-			for bi, branch in node.branches {
+			for _, branch in node.branches {
 				used_values_count += branch.exprs.len
 				for bi_ei, bexpr in branch.exprs {
 					match bexpr {
diff --git a/vlib/v/checker/tests/inout/match_err.vv b/vlib/v/checker/tests/inout/match_err.vv
index f83c93155e..952e4b768b 100644
--- a/vlib/v/checker/tests/inout/match_err.vv
+++ b/vlib/v/checker/tests/inout/match_err.vv
@@ -6,4 +6,5 @@ fn main() {
 		2 { 'test' }
 		else { '' }
 	}
+	_ = res
 }
diff --git a/vlib/v/checker/tests/inout/match_expr_else.out b/vlib/v/checker/tests/inout/match_expr_else.out
index 962a3b44ce..2544b8f7fd 100644
--- a/vlib/v/checker/tests/inout/match_expr_else.out
+++ b/vlib/v/checker/tests/inout/match_expr_else.out
@@ -1,7 +1,7 @@
-vlib/v/checker/tests/inout/match_expr_else.v:5:9: error: match must be exhaustive (add match branches for: `f64` or an else{} branch)
+vlib/v/checker/tests/inout/match_expr_else.v:5:6: error: match must be exhaustive (add match branches for: `f64` or an else{} branch)
     3| fn main() {
     4|     x := A('test')
-    5|     res := match x {
-                  ~~~~~~~~~
+    5|     _ = match x {
+               ~~~~~~~~~
     6|         int {
     7|             'int'
diff --git a/vlib/v/checker/tests/inout/match_expr_else.vv b/vlib/v/checker/tests/inout/match_expr_else.vv
index d32dabd9f2..d120acbd19 100644
--- a/vlib/v/checker/tests/inout/match_expr_else.vv
+++ b/vlib/v/checker/tests/inout/match_expr_else.vv
@@ -2,7 +2,7 @@ type A = int | string | f64
 
 fn main() {
 	x := A('test')
-	res := match x {
+	_ = match x {
 		int {
 			'int'
 		}
diff --git a/vlib/v/checker/tests/inout/short_struct_too_many.out b/vlib/v/checker/tests/inout/short_struct_too_many.out
index b403965637..7a0e28d331 100644
--- a/vlib/v/checker/tests/inout/short_struct_too_many.out
+++ b/vlib/v/checker/tests/inout/short_struct_too_many.out
@@ -3,4 +3,5 @@ vlib/v/checker/tests/inout/short_struct_too_many.v:6:7: error: too many fields
     5| fn main() {
     6|     t := Test{true, false}
                 ~~~~~~~~~~~~~~~~~
-    7| }
\ No newline at end of file
+    7|     _ = t
+    8| }
diff --git a/vlib/v/checker/tests/inout/short_struct_too_many.vv b/vlib/v/checker/tests/inout/short_struct_too_many.vv
index a707dc3513..d33acc614d 100644
--- a/vlib/v/checker/tests/inout/short_struct_too_many.vv
+++ b/vlib/v/checker/tests/inout/short_struct_too_many.vv
@@ -4,4 +4,5 @@ struct Test {
 
 fn main() {
 	t := Test{true, false}
+	_ = t
 }
diff --git a/vlib/v/checker/tests/inout/struct_unknown_field.out b/vlib/v/checker/tests/inout/struct_unknown_field.out
index 1e2d6577b7..9e01e772a3 100644
--- a/vlib/v/checker/tests/inout/struct_unknown_field.out
+++ b/vlib/v/checker/tests/inout/struct_unknown_field.out
@@ -4,4 +4,4 @@ vlib/v/checker/tests/inout/struct_unknown_field.v:8:9: error: unknown field `bar
     8|         bar: false
                ~~~~~~~~~~
     9|     }
-   10| }
+   10|      _ = t
diff --git a/vlib/v/checker/tests/inout/struct_unknown_field.vv b/vlib/v/checker/tests/inout/struct_unknown_field.vv
index 8a1145d01e..e4ec496630 100644
--- a/vlib/v/checker/tests/inout/struct_unknown_field.vv
+++ b/vlib/v/checker/tests/inout/struct_unknown_field.vv
@@ -7,4 +7,5 @@ fn main() {
         foo: true
         bar: false
     }
+	 _ = t
 }
diff --git a/vlib/v/checker/tests/inout/void_fn_as_value.out b/vlib/v/checker/tests/inout/void_fn_as_value.out
index 0ad36288a4..94eb71e5d0 100644
--- a/vlib/v/checker/tests/inout/void_fn_as_value.out
+++ b/vlib/v/checker/tests/inout/void_fn_as_value.out
@@ -4,4 +4,4 @@ vlib/v/checker/tests/inout/void_fn_as_value.v:5:8: error: unknown function: x
     5|   a += x('a','b')
               ~~~~~~~~~~
     6|   mut b := 'abcdef'
-    7| }
+    7|   _ = b
diff --git a/vlib/v/checker/tests/inout/void_fn_as_value.vv b/vlib/v/checker/tests/inout/void_fn_as_value.vv
index d88cc2d871..4d6f97dc39 100644
--- a/vlib/v/checker/tests/inout/void_fn_as_value.vv
+++ b/vlib/v/checker/tests/inout/void_fn_as_value.vv
@@ -4,4 +4,5 @@ fn main() {
   mut a := 'aa'
   a += x('a','b')
   mut b := 'abcdef'
+  _ = b
 }
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index 00f145d308..c1ee187887 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -94,6 +94,8 @@ pub fn cgen(files []ast.File, table &table.Table, pref &pref.Preferences) string
 		x := 10 // line
 		// sep
 		y := 20
+		_ = x
+		_ = y
 	} else {
 	}
 	// println('start cgen2')
@@ -919,7 +921,7 @@ fn (mut g Gen) expr(node ast.Expr) {
 		ast.ArrayInit {
 			type_sym := g.table.get_type_symbol(it.typ)
 			if type_sym.kind != .array_fixed {
-				elem_sym := g.table.get_type_symbol(it.elem_type)
+				// elem_sym := g.table.get_type_symbol(it.elem_type)
 				elem_type_str := g.typ(it.elem_type)
 				if it.exprs.len == 0 {
 					// use __new_array to fix conflicts when the name of the variable is new_array
@@ -1801,8 +1803,8 @@ fn (mut g Gen) return_statement(node ast.Return) {
 	// multiple returns
 	if node.exprs.len > 1 {
 		g.write(' ')
-		typ_sym := g.table.get_type_symbol(g.fn_decl.return_type)
-		mr_info := typ_sym.info as table.MultiReturn
+		// typ_sym := g.table.get_type_symbol(g.fn_decl.return_type)
+		// mr_info := typ_sym.info as table.MultiReturn
 		mut styp := g.typ(g.fn_decl.return_type)
 		if fn_return_is_optional { // && !table.type_is(node.types[0], .optional) && node.types[0] !=
 			styp = styp[7..] // remove 'Option_'
@@ -1958,7 +1960,7 @@ fn (mut g Gen) struct_init(struct_init ast.StructInit) {
 	}
 */
 	// User set fields
-	for i, field in struct_init.fields {
+	for _, field in struct_init.fields {
 		field_name := c_name(field.name)
 		inited_fields << field.name
 		g.write('\t.$field_name = ')
diff --git a/vlib/v/gen/js/js.v b/vlib/v/gen/js/js.v
index 6812c0d2b8..6a61cfd457 100644
--- a/vlib/v/gen/js/js.v
+++ b/vlib/v/gen/js/js.v
@@ -594,7 +594,7 @@ fn (g mut JsGen) gen_branch_stmt(it ast.BranchStmt) {
 }
 
 fn (g mut JsGen) gen_const_decl(it ast.ConstDecl) {
-	old_indent := g.indents[g.namespace]
+	// old_indent := g.indents[g.namespace]
 	for i, field in it.fields {
 		// TODO hack. Cut the generated value and paste it into definitions.
 		pos := g.out.len
@@ -689,7 +689,7 @@ fn (g mut JsGen) gen_method_decl(it ast.FnDecl) {
 			name = util.replace_op(name)
 		}
 
-		type_name := g.typ(it.return_type)
+		// type_name := g.typ(it.return_type)
 
 		// generate jsdoc for the function
 		g.writeln(g.doc.gen_fn(it))
@@ -767,7 +767,7 @@ fn (g mut JsGen) gen_for_in_stmt(it ast.ForInStmt) {
 	} else if it.kind == .array || table.type_is(it.cond_type, .variadic) {
 		// `for num in nums {`
 		i := if it.key_var == '' { g.new_tmp_var() } else { it.key_var }
-		styp := g.typ(it.val_type)
+		// styp := g.typ(it.val_type)
 		g.inside_loop = true
 		g.write('for (let $i = 0; $i < ')
 		g.expr(it.cond)
@@ -780,8 +780,8 @@ fn (g mut JsGen) gen_for_in_stmt(it ast.ForInStmt) {
 		g.writeln('}')
 	} else if it.kind == .map {
 		// `for key, val in map[string]int {`
-		key_styp := g.typ(it.key_type)
-		val_styp := g.typ(it.val_type)
+		// key_styp := g.typ(it.key_type)
+		// val_styp := g.typ(it.val_type)
 		key := if it.key_var == '' { g.new_tmp_var() } else { it.key_var }
 		g.write('for (let [$key, $it.val_var] of ')
 		g.expr(it.cond)
@@ -817,7 +817,7 @@ fn (g mut JsGen) gen_for_stmt(it ast.ForStmt) {
 }
 
 fn (g mut JsGen) fn_args(args []table.Arg, is_variadic bool) {
-	no_names := args.len > 0 && args[0].name == 'arg_1'
+	// no_names := args.len > 0 && args[0].name == 'arg_1'
 	for i, arg in args {
 		is_varg := i == args.len - 1 && is_variadic
 		if is_varg {
@@ -860,10 +860,10 @@ fn (g mut JsGen) gen_go_stmt(node ast.GoStmt) {
 }
 
 fn (g mut JsGen) gen_map_init_expr(it ast.MapInit) {
-	key_typ_sym := g.table.get_type_symbol(it.key_type)
-	value_typ_sym := g.table.get_type_symbol(it.value_type)
-	key_typ_str := key_typ_sym.name.replace('.', '__')
-	value_typ_str := value_typ_sym.name.replace('.', '__')
+	// key_typ_sym := g.table.get_type_symbol(it.key_type)
+	// value_typ_sym := g.table.get_type_symbol(it.value_type)
+	// key_typ_str := key_typ_sym.name.replace('.', '__')
+	// value_typ_str := value_typ_sym.name.replace('.', '__')
 	if it.vals.len > 0 {
 		g.writeln('new Map([')
 		g.inc_indent()
diff --git a/vlib/v/parser/containers.v b/vlib/v/parser/containers.v
index e29772bd59..157a18d76f 100644
--- a/vlib/v/parser/containers.v
+++ b/vlib/v/parser/containers.v
@@ -43,6 +43,7 @@ fn (var p Parser) array_init() ast.ArrayInit {
 			// NB: do not remove the next line without testing
 			// v selfcompilation with tcc first
 			tcc_stack_bug := 12345
+			_ = tcc_stack_bug
 		}
 		last_pos = p.tok.position()
 		p.check(.rsbr)
diff --git a/vlib/v/parser/fn.v b/vlib/v/parser/fn.v
index 8140717cdf..c2117b5acd 100644
--- a/vlib/v/parser/fn.v
+++ b/vlib/v/parser/fn.v
@@ -11,7 +11,6 @@ import v.util
 
 pub fn (mut p Parser) call_expr(is_c, is_js bool, mod string) ast.CallExpr {
 	first_pos := p.tok.position()
-	tok := p.tok
 	name := p.check_name()
 	fn_name := if is_c {
 		'C.$name'
diff --git a/vlib/v/parser/for.v b/vlib/v/parser/for.v
index f6ff6f78f4..8b8621463f 100644
--- a/vlib/v/parser/for.v
+++ b/vlib/v/parser/for.v
@@ -43,7 +43,6 @@ fn (var p Parser) for_stmt() ast.Stmt {
 		// Allow `for i = 0; i < ...`
 		p.check(.semicolon)
 		if p.tok.kind != .semicolon {
-			var typ := table.void_type
 			cond = p.expr(0)
 			has_cond = true
 		}
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index 90a2bf397d..6e4bfe4904 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -192,6 +192,16 @@ pub fn (mut p Parser) open_scope() {
 }
 
 pub fn (mut p Parser) close_scope() {
+	if !p.pref.is_repl {
+		for v in p.scope.unused_vars() {
+			if p.pref.is_prod {
+				p.error_with_pos('Unused variable: $v.name', v.pos)
+			} else {
+				p.warn_with_pos('Unused variable: $v.name', v.pos)
+			}
+		}
+	}
+  p.scope.clear_unused_vars()
 	p.scope.end_pos = p.tok.pos
 	p.scope.parent.children << p.scope
 	p.scope = p.scope.parent
@@ -376,6 +386,9 @@ pub fn (mut p Parser) stmt() ast.Stmt {
 			}
 		}
 		.key_mut, .key_static, .key_var {
+			if p.peek_tok.kind == .name && p.peek_tok.lit != '_' && !p.peek_tok.lit.starts_with('__') {
+				p.scope.register_unused_var(p.peek_tok.lit, p.peek_tok.position())
+			}
 			return p.assign_stmt()
 		}
 		.key_for {
@@ -437,7 +450,14 @@ pub fn (mut p Parser) stmt() ast.Stmt {
 		else {
 			// `x := ...`
 			if p.tok.kind == .name && p.peek_tok.kind in [.decl_assign, .comma] {
-				return p.assign_stmt()
+				register_unused := p.peek_tok.kind == .decl_assign
+				lit := p.tok.lit
+				pos := p.tok.position()
+				ret := p.assign_stmt()
+				if register_unused && lit != '_' && !lit.starts_with('__') {
+					p.scope.register_unused_var(lit, pos)
+				}
+				return ret
 			} else if p.tok.kind == .name && p.peek_tok.kind == .colon {
 				// `label:`
 				name := p.check_name()
@@ -445,6 +465,8 @@ pub fn (mut p Parser) stmt() ast.Stmt {
 				return ast.GotoLabel{
 					name: name
 				}
+			} else if p.tok.kind == .name {
+				p.scope.remove_unused_var(p.tok.lit)
 			}
 			epos := p.tok.position()
 			expr := p.expr(0)
@@ -994,6 +1016,9 @@ fn (mut p Parser) return_stmt() ast.Return {
 		}
 	}
 	for {
+		if p.tok.kind == .name {
+			p.scope.remove_unused_var(p.tok.lit)
+		}
 		expr := p.expr(0)
 		exprs << expr
 		if p.tok.kind == .comma {
diff --git a/vlib/v/parser/pratt.v b/vlib/v/parser/pratt.v
index 5b859175cb..c3c300bf8d 100644
--- a/vlib/v/parser/pratt.v
+++ b/vlib/v/parser/pratt.v
@@ -16,6 +16,7 @@ pub fn (mut p Parser) expr(precedence int) ast.Expr {
 	// Prefix
 	match p.tok.kind {
 		.name {
+			p.scope.remove_unused_var(p.tok.lit)
 			node = p.name_expr()
 			p.is_stmt_ident = is_stmt_ident
 		}
@@ -78,6 +79,7 @@ pub fn (mut p Parser) expr(precedence int) ast.Expr {
 					type_name: p.check_name()
 				}
 			} else {
+				p.scope.remove_unused_var(p.tok.lit)
 				sizeof_type := p.parse_type()
 				node = ast.SizeOf{
 					typ: sizeof_type
@@ -102,6 +104,7 @@ pub fn (mut p Parser) expr(precedence int) ast.Expr {
 			} else {
 				// it should be a struct
 				if p.peek_tok.kind == .pipe {
+					p.scope.remove_unused_var(p.tok.lit)
 					node = p.assoc()
 				} else if p.peek_tok.kind == .colon || p.tok.kind == .rcbr {
 					node = p.struct_init(true) // short_syntax: true
diff --git a/vlib/v/tests/prod/assoc.prod.v b/vlib/v/tests/prod/assoc.prod.v
index 18845a14e2..406a29b378 100644
--- a/vlib/v/tests/prod/assoc.prod.v
+++ b/vlib/v/tests/prod/assoc.prod.v
@@ -1,13 +1,16 @@
 struct MyStruct {
-    s string
+	s string
 }
+
 fn new_st() MyStruct {
-    return MyStruct{}
+	return MyStruct{}
 }
+
 fn get_st() MyStruct {
-    r := new_st() 
-    return {r|s:'6'}
+	r := new_st()
+	return {r|s:'6'}
 }
+
 fn main() {
     s := get_st()
     println(s)