From 85cb0a8c85dd3df7fc0701b82b4ba1a879e113ae Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20D=C3=A4schle?= <daniel.daeschle@gmail.com>
Date: Sat, 30 Apr 2022 00:59:14 +0200
Subject: [PATCH] all: basic implementation of result type (#14140)

---
 vlib/builtin/option.v                         |  16 ++
 vlib/v/ast/ast.v                              |   3 +-
 vlib/v/ast/str.v                              |   5 +-
 vlib/v/ast/table.v                            |   6 +-
 vlib/v/ast/types.v                            |   8 +
 vlib/v/checker/check_types.v                  |   9 +-
 vlib/v/checker/checker.v                      |  59 ++++--
 vlib/v/checker/fn.v                           |  12 +-
 vlib/v/checker/return.v                       |   2 +-
 vlib/v/checker/str.v                          |   2 +-
 vlib/v/checker/tests/fn_return_or_err.out     |   4 +-
 vlib/v/checker/tests/go_wait_or.out           |   8 +-
 .../propagate_option_with_result_err.out      |   7 +
 .../tests/propagate_option_with_result_err.vv |  10 +
 .../tests/propagate_result_with_option.out    |   7 +
 .../tests/propagate_result_with_option.vv     |  10 +
 vlib/v/checker/tests/unexpected_or.out        |   2 +-
 .../checker/tests/unexpected_or_propagate.out |   2 +-
 vlib/v/fmt/fmt.v                              |   7 +-
 vlib/v/fmt/tests/result_return_type_keep.vv   |   3 +
 vlib/v/gen/c/assert.v                         |   2 +-
 vlib/v/gen/c/auto_str_methods.v               |  42 ++++-
 vlib/v/gen/c/cgen.v                           | 176 +++++++++++++++++-
 vlib/v/gen/c/fn.v                             |   5 +-
 vlib/v/gen/c/str_intp.v                       |   3 +-
 vlib/v/gen/js/auto_str_methods.v              |   2 +
 vlib/v/gen/js/fn.v                            |  10 +-
 vlib/v/gen/js/js.v                            |   2 +-
 vlib/v/parser/expr.v                          |   4 +-
 vlib/v/parser/fn.v                            |   9 +-
 vlib/v/parser/parse_type.v                    |  23 ++-
 vlib/v/parser/parser.v                        |  12 +-
 vlib/v/parser/tests/option_result_err.out     |   5 +
 vlib/v/parser/tests/option_result_err.vv      |   3 +
 vlib/v/parser/tests/result_option_err.out     |   5 +
 vlib/v/parser/tests/result_option_err.vv      |   3 +
 vlib/v/scanner/scanner.v                      |   2 +-
 vlib/v/tests/results_test.v                   |  65 +++++++
 vlib/v/token/token.v                          |   2 +-
 39 files changed, 478 insertions(+), 79 deletions(-)
 create mode 100644 vlib/v/checker/tests/propagate_option_with_result_err.out
 create mode 100644 vlib/v/checker/tests/propagate_option_with_result_err.vv
 create mode 100644 vlib/v/checker/tests/propagate_result_with_option.out
 create mode 100644 vlib/v/checker/tests/propagate_result_with_option.vv
 create mode 100644 vlib/v/fmt/tests/result_return_type_keep.vv
 create mode 100644 vlib/v/parser/tests/option_result_err.out
 create mode 100644 vlib/v/parser/tests/option_result_err.vv
 create mode 100644 vlib/v/parser/tests/result_option_err.out
 create mode 100644 vlib/v/parser/tests/result_option_err.vv
 create mode 100644 vlib/v/tests/results_test.v

diff --git a/vlib/builtin/option.v b/vlib/builtin/option.v
index 2cfcc55388..d487595d8b 100644
--- a/vlib/builtin/option.v
+++ b/vlib/builtin/option.v
@@ -118,6 +118,22 @@ fn opt_ok(data voidptr, mut option Option, size int) {
 	}
 }
 
+struct result {
+	is_error bool
+	err      IError = none__
+	// Data is trailing after err
+	// and is not included in here but in the
+	// derived Result_xxx types
+}
+
+fn result_ok(data voidptr, mut res result, size int) {
+	unsafe {
+		*res = result{}
+		// use err to get the end of ResultBase and then memcpy into it
+		vmemcpy(&u8(&res.err) + sizeof(IError), data, size)
+	}
+}
+
 pub fn (_ none) str() string {
 	return 'none'
 }
diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index b2244306c8..06fb9a1bf7 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -1487,7 +1487,8 @@ pub mut:
 pub enum OrKind {
 	absent
 	block
-	propagate
+	propagate_option
+	propagate_result
 }
 
 // `or { ... }`
diff --git a/vlib/v/ast/str.v b/vlib/v/ast/str.v
index f80a877379..9ef7494d07 100644
--- a/vlib/v/ast/str.v
+++ b/vlib/v/ast/str.v
@@ -210,7 +210,8 @@ pub fn (lit &StringInterLiteral) get_fspec_braces(i int) (string, bool) {
 				}
 				CallExpr {
 					if sub_expr.args.len != 0 || sub_expr.concrete_types.len != 0
-						|| sub_expr.or_block.kind == .propagate || sub_expr.or_block.stmts.len > 0 {
+						|| sub_expr.or_block.kind == .propagate_option
+						|| sub_expr.or_block.stmts.len > 0 {
 						needs_braces = true
 					} else if sub_expr.left is CallExpr {
 						sub_expr = sub_expr.left
@@ -302,7 +303,7 @@ pub fn (x Expr) str() string {
 		}
 		CallExpr {
 			sargs := args2str(x.args)
-			propagate_suffix := if x.or_block.kind == .propagate { ' ?' } else { '' }
+			propagate_suffix := if x.or_block.kind == .propagate_option { ' ?' } else { '' }
 			if x.is_method {
 				return '${x.left.str()}.${x.name}($sargs)$propagate_suffix'
 			}
diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index 79c5a95d3d..20d1951934 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -232,7 +232,7 @@ pub fn (t &Table) fn_type_signature(f &Fn) string {
 	return sig
 }
 
-// source_signature generates the signature of a function which looks like in the V source
+// fn_type_source_signature generates the signature of a function which looks like in the V source
 pub fn (t &Table) fn_type_source_signature(f &Fn) string {
 	mut sig := '('
 	for i, arg in f.params {
@@ -252,10 +252,14 @@ pub fn (t &Table) fn_type_source_signature(f &Fn) string {
 	sig += ')'
 	if f.return_type == ovoid_type {
 		sig += ' ?'
+	} else if f.return_type == rvoid_type {
+		sig += ' !'
 	} else if f.return_type != void_type {
 		return_type_sym := t.sym(f.return_type)
 		if f.return_type.has_flag(.optional) {
 			sig += ' ?$return_type_sym.name'
+		} else if f.return_type.has_flag(.result) {
+			sig += ' !$return_type_sym.name'
 		} else {
 			sig += ' $return_type_sym.name'
 		}
diff --git a/vlib/v/ast/types.v b/vlib/v/ast/types.v
index 97935bafac..515f179e81 100644
--- a/vlib/v/ast/types.v
+++ b/vlib/v/ast/types.v
@@ -98,6 +98,7 @@ pub mut:
 // max of 8
 pub enum TypeFlag {
 	optional
+	result
 	variadic
 	generic
 	shared_f
@@ -472,6 +473,7 @@ pub const (
 pub const (
 	void_type          = new_type(void_type_idx)
 	ovoid_type         = new_type(void_type_idx).set_flag(.optional) // the return type of `fn () ?`
+	rvoid_type         = new_type(void_type_idx).set_flag(.result) // the return type of `fn () !`
 	voidptr_type       = new_type(voidptr_type_idx)
 	byteptr_type       = new_type(byteptr_type_idx)
 	charptr_type       = new_type(charptr_type_idx)
@@ -1227,6 +1229,9 @@ pub fn (t &Table) type_to_str_using_aliases(typ Type, import_aliases map[string]
 			if typ.has_flag(.optional) {
 				return '?'
 			}
+			if typ.has_flag(.result) {
+				return '!'
+			}
 			return 'void'
 		}
 		.thread {
@@ -1262,6 +1267,9 @@ pub fn (t &Table) type_to_str_using_aliases(typ Type, import_aliases map[string]
 	if typ.has_flag(.optional) {
 		res = '?$res'
 	}
+	if typ.has_flag(.result) {
+		res = '!$res'
+	}
 	return res
 }
 
diff --git a/vlib/v/checker/check_types.v b/vlib/v/checker/check_types.v
index 6c846a1db0..9d2bb65a50 100644
--- a/vlib/v/checker/check_types.v
+++ b/vlib/v/checker/check_types.v
@@ -89,12 +89,15 @@ pub fn (mut c Checker) check_types(got ast.Type, expected ast.Type) bool {
 	if expected == ast.charptr_type && got == ast.char_type.ref() {
 		return true
 	}
-	if expected.has_flag(.optional) {
+	if expected.has_flag(.optional) || expected.has_flag(.result) {
 		sym := c.table.sym(got)
-		if sym.idx == ast.error_type_idx || got in [ast.none_type, ast.error_type] {
+		if ((sym.idx == ast.error_type_idx || got in [ast.none_type, ast.error_type])
+			&& expected.has_flag(.optional))
+			|| ((sym.idx == ast.error_type_idx || got == ast.error_type)
+			&& expected.has_flag(.result)) {
 			// IErorr
 			return true
-		} else if !c.check_basic(got, expected.clear_flag(.optional)) {
+		} else if !c.check_basic(got, expected.clear_flag(.optional).clear_flag(.result)) {
 			return false
 		}
 	}
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 4627e0d123..3bdbf50278 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1488,39 +1488,61 @@ fn (mut c Checker) type_implements(typ ast.Type, interface_type ast.Type, pos to
 // return the actual type of the expression, once the optional is handled
 pub fn (mut c Checker) check_expr_opt_call(expr ast.Expr, ret_type ast.Type) ast.Type {
 	if expr is ast.CallExpr {
-		if expr.return_type.has_flag(.optional) {
+		if expr.return_type.has_flag(.optional) || expr.return_type.has_flag(.result) {
+			return_modifier_kind := if expr.return_type.has_flag(.optional) {
+				'an option'
+			} else {
+				'a result'
+			}
+			return_modifier := if expr.return_type.has_flag(.optional) { '?' } else { '!' }
 			if expr.or_block.kind == .absent {
 				if c.inside_defer {
-					c.error('${expr.name}() returns an option, so it should have an `or {}` block at the end',
+					c.error('${expr.name}() returns $return_modifier_kind, so it should have an `or {}` block at the end',
 						expr.pos)
 				} else {
-					c.error('${expr.name}() returns an option, so it should have either an `or {}` block, or `?` at the end',
+					c.error('${expr.name}() returns $return_modifier_kind, so it should have either an `or {}` block, or `$return_modifier` at the end',
 						expr.pos)
 				}
 			} else {
-				c.check_or_expr(expr.or_block, ret_type, expr.return_type.clear_flag(.optional))
+				c.check_or_expr(expr.or_block, ret_type, expr.return_type)
 			}
 			return ret_type.clear_flag(.optional)
 		} else if expr.or_block.kind == .block {
-			c.error('unexpected `or` block, the function `$expr.name` does not return an optional',
+			c.error('unexpected `or` block, the function `$expr.name` does neither return an optional nor a result',
 				expr.or_block.pos)
-		} else if expr.or_block.kind == .propagate {
+		} else if expr.or_block.kind == .propagate_option {
 			c.error('unexpected `?`, the function `$expr.name` does not return an optional',
 				expr.or_block.pos)
 		}
 	} else if expr is ast.IndexExpr {
 		if expr.or_expr.kind != .absent {
-			c.check_or_expr(expr.or_expr, ret_type, ret_type)
+			c.check_or_expr(expr.or_expr, ret_type, ret_type.set_flag(.optional))
 		}
 	}
 	return ret_type
 }
 
 pub fn (mut c Checker) check_or_expr(node ast.OrExpr, ret_type ast.Type, expr_return_type ast.Type) {
-	if node.kind == .propagate {
+	if node.kind == .propagate_option {
 		if !c.table.cur_fn.return_type.has_flag(.optional) && c.table.cur_fn.name != 'main.main'
 			&& !c.inside_const {
-			c.error('to propagate the optional call, `$c.table.cur_fn.name` must return an optional',
+			c.error('to propagate the call, `$c.table.cur_fn.name` must return an optional type',
+				node.pos)
+		}
+		if !expr_return_type.has_flag(.optional) {
+			c.error('to propagate an option, the call must also return an optional type',
+				node.pos)
+		}
+		return
+	}
+	if node.kind == .propagate_result {
+		if !c.table.cur_fn.return_type.has_flag(.result) && c.table.cur_fn.name != 'main.main'
+			&& !c.inside_const {
+			c.error('to propagate the call, `$c.table.cur_fn.name` must return an result type',
+				node.pos)
+		}
+		if !expr_return_type.has_flag(.result) {
+			c.error('to propagate a result, the call must also return a result type',
 				node.pos)
 		}
 		return
@@ -1535,7 +1557,7 @@ pub fn (mut c Checker) check_or_expr(node ast.OrExpr, ret_type ast.Type, expr_re
 		return
 	}
 	last_stmt := node.stmts[stmts_len - 1]
-	c.check_or_last_stmt(last_stmt, ret_type, expr_return_type)
+	c.check_or_last_stmt(last_stmt, ret_type, expr_return_type.clear_flag(.optional).clear_flag(.result))
 }
 
 fn (mut c Checker) check_or_last_stmt(stmt ast.Stmt, ret_type ast.Type, expr_return_type ast.Type) {
@@ -2600,17 +2622,22 @@ pub fn (mut c Checker) expr(node_ ast.Expr) ast.Type {
 		}
 		ast.CallExpr {
 			mut ret_type := c.call_expr(mut node)
-			if !ret_type.has_flag(.optional) {
+			if !ret_type.has_flag(.optional) && !ret_type.has_flag(.result) {
 				if node.or_block.kind == .block {
-					c.error('unexpected `or` block, the function `$node.name` does not return an optional',
+					c.error('unexpected `or` block, the function `$node.name` does neither return an optional nor a result',
 						node.or_block.pos)
-				} else if node.or_block.kind == .propagate {
-					c.error('unexpected `?`, the function `$node.name` does not return an optional',
+				} else if node.or_block.kind == .propagate_option {
+					c.error('unexpected `?`, the function `$node.name` does neither return an optional nor a result',
 						node.or_block.pos)
 				}
 			}
-			if ret_type.has_flag(.optional) && node.or_block.kind != .absent {
-				ret_type = ret_type.clear_flag(.optional)
+			if node.or_block.kind != .absent {
+				if ret_type.has_flag(.optional) {
+					ret_type = ret_type.clear_flag(.optional)
+				}
+				if ret_type.has_flag(.result) {
+					ret_type = ret_type.clear_flag(.result)
+				}
 			}
 			return ret_type
 		}
diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index 1c8e2ea042..d1072743c8 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -310,6 +310,16 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			}
 		}
 	}
+	// same for result `fn (...) ! { ... }`
+	if node.return_type != ast.void_type && node.return_type.has_flag(.result)
+		&& (node.stmts.len == 0 || node.stmts.last() !is ast.Return) {
+		sym := c.table.sym(node.return_type)
+		if sym.kind == .void {
+			node.stmts << ast.Return{
+				pos: node.pos
+			}
+		}
+	}
 	c.fn_scope = node.scope
 	c.stmts(node.stmts)
 	node_has_top_return := has_top_return(node.stmts)
@@ -411,7 +421,7 @@ pub fn (mut c Checker) call_expr(mut node ast.CallExpr) ast.Type {
 	c.expected_or_type = node.return_type.clear_flag(.optional)
 	c.stmts_ending_with_expression(node.or_block.stmts)
 	c.expected_or_type = ast.void_type
-	if node.or_block.kind == .propagate && !c.table.cur_fn.return_type.has_flag(.optional)
+	if node.or_block.kind == .propagate_option && !c.table.cur_fn.return_type.has_flag(.optional)
 		&& !c.inside_const {
 		if !c.table.cur_fn.is_main {
 			c.error('to propagate the optional call, `$c.table.cur_fn.name` must return an optional',
diff --git a/vlib/v/checker/return.v b/vlib/v/checker/return.v
index f442826d95..08fce331e0 100644
--- a/vlib/v/checker/return.v
+++ b/vlib/v/checker/return.v
@@ -158,7 +158,7 @@ pub fn (mut c Checker) return_stmt(mut node ast.Return) {
 	if exp_is_optional && node.exprs.len > 0 {
 		expr0 := node.exprs[0]
 		if expr0 is ast.CallExpr {
-			if expr0.or_block.kind == .propagate && node.exprs.len == 1 {
+			if expr0.or_block.kind == .propagate_option && node.exprs.len == 1 {
 				c.error('`?` is not needed, use `return ${expr0.name}()`', expr0.pos)
 			}
 		}
diff --git a/vlib/v/checker/str.v b/vlib/v/checker/str.v
index 8f3ed9c223..fa1575e00b 100644
--- a/vlib/v/checker/str.v
+++ b/vlib/v/checker/str.v
@@ -7,7 +7,7 @@ import v.ast
 import v.token
 
 pub fn (mut c Checker) get_default_fmt(ftyp ast.Type, typ ast.Type) u8 {
-	if ftyp.has_flag(.optional) {
+	if ftyp.has_flag(.optional) || ftyp.has_flag(.result) {
 		return `s`
 	} else if typ.is_float() {
 		return `g`
diff --git a/vlib/v/checker/tests/fn_return_or_err.out b/vlib/v/checker/tests/fn_return_or_err.out
index ebb4494d27..3da8179470 100644
--- a/vlib/v/checker/tests/fn_return_or_err.out
+++ b/vlib/v/checker/tests/fn_return_or_err.out
@@ -1,5 +1,5 @@
-vlib/v/checker/tests/fn_return_or_err.vv:6:17: error: unexpected `or` block, the function `pop` does not return an optional
-    4 |
+vlib/v/checker/tests/fn_return_or_err.vv:6:17: error: unexpected `or` block, the function `pop` does neither return an optional nor a result
+    4 | 
     5 | pub fn next(mut v []Typ) Typ {
     6 |     return v.pop() or { Typ{} }
       |                    ~~~~~~~~~~~~
diff --git a/vlib/v/checker/tests/go_wait_or.out b/vlib/v/checker/tests/go_wait_or.out
index 146f4fbbf4..d00dbd2209 100644
--- a/vlib/v/checker/tests/go_wait_or.out
+++ b/vlib/v/checker/tests/go_wait_or.out
@@ -1,25 +1,25 @@
-vlib/v/checker/tests/go_wait_or.vv:11:17: error: unexpected `?`, the function `wait` does not return an optional
+vlib/v/checker/tests/go_wait_or.vv:11:17: error: unexpected `?`, the function `wait` does neither return an optional nor a result
     9 |         go d(1)
    10 |     ]
    11 |     r := tg.wait() ?
       |                    ^
    12 |     println(r)
    13 |     s := tg[0].wait() or { panic('problem') }
-vlib/v/checker/tests/go_wait_or.vv:13:20: error: unexpected `or` block, the function `wait` does not return an optional
+vlib/v/checker/tests/go_wait_or.vv:13:20: error: unexpected `or` block, the function `wait` does neither return an optional nor a result
    11 |     r := tg.wait() ?
    12 |     println(r)
    13 |     s := tg[0].wait() or { panic('problem') }
       |                       ~~~~~~~~~~~~~~~~~~~~~~~
    14 |     println(s)
    15 |     tg2 := [
-vlib/v/checker/tests/go_wait_or.vv:19:13: error: unexpected `or` block, the function `wait` does not return an optional
+vlib/v/checker/tests/go_wait_or.vv:19:13: error: unexpected `or` block, the function `wait` does neither return an optional nor a result
    17 |         go e(1)
    18 |     ]
    19 |     tg2.wait() or { panic('problem') }
       |                ~~~~~~~~~~~~~~~~~~~~~~~
    20 |     tg2[0].wait() ?
    21 |     tg3 := [
-vlib/v/checker/tests/go_wait_or.vv:20:16: error: unexpected `?`, the function `wait` does not return an optional
+vlib/v/checker/tests/go_wait_or.vv:20:16: error: unexpected `?`, the function `wait` does neither return an optional nor a result
    18 |     ]
    19 |     tg2.wait() or { panic('problem') }
    20 |     tg2[0].wait() ?
diff --git a/vlib/v/checker/tests/propagate_option_with_result_err.out b/vlib/v/checker/tests/propagate_option_with_result_err.out
new file mode 100644
index 0000000000..edbb23304c
--- /dev/null
+++ b/vlib/v/checker/tests/propagate_option_with_result_err.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/propagate_option_with_result_err.vv:6:8: error: to propagate an option, the call must also return an optional type
+    4 | 
+    5 | fn bar() ?string {
+    6 |     foo() ?
+      |           ^
+    7 |     return ''
+    8 | }
diff --git a/vlib/v/checker/tests/propagate_option_with_result_err.vv b/vlib/v/checker/tests/propagate_option_with_result_err.vv
new file mode 100644
index 0000000000..0b57053fbb
--- /dev/null
+++ b/vlib/v/checker/tests/propagate_option_with_result_err.vv
@@ -0,0 +1,10 @@
+fn foo() !string {
+	return ''
+}
+
+fn bar() ?string {
+	foo() ?
+	return ''
+}
+
+fn main() {}
diff --git a/vlib/v/checker/tests/propagate_result_with_option.out b/vlib/v/checker/tests/propagate_result_with_option.out
new file mode 100644
index 0000000000..d54af05115
--- /dev/null
+++ b/vlib/v/checker/tests/propagate_result_with_option.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/propagate_result_with_option.vv:6:8: error: to propagate a result, the call must also return a result type
+    4 | 
+    5 | fn bar() !string {
+    6 |     foo() !
+      |           ^
+    7 |     return ''
+    8 | }
diff --git a/vlib/v/checker/tests/propagate_result_with_option.vv b/vlib/v/checker/tests/propagate_result_with_option.vv
new file mode 100644
index 0000000000..8025c9f638
--- /dev/null
+++ b/vlib/v/checker/tests/propagate_result_with_option.vv
@@ -0,0 +1,10 @@
+fn foo() ?string {
+	return ''
+}
+
+fn bar() !string {
+	foo() !
+	return ''
+}
+
+fn main() {}
diff --git a/vlib/v/checker/tests/unexpected_or.out b/vlib/v/checker/tests/unexpected_or.out
index ab1e077c69..03eeaea331 100644
--- a/vlib/v/checker/tests/unexpected_or.out
+++ b/vlib/v/checker/tests/unexpected_or.out
@@ -1,4 +1,4 @@
-vlib/v/checker/tests/unexpected_or.vv:6:17: error: unexpected `or` block, the function `ret_zero` does not return an optional
+vlib/v/checker/tests/unexpected_or.vv:6:17: error: unexpected `or` block, the function `ret_zero` does neither return an optional nor a result
     4 | 
     5 | fn main() {
     6 |     _ = ret_zero() or { 1 }
diff --git a/vlib/v/checker/tests/unexpected_or_propagate.out b/vlib/v/checker/tests/unexpected_or_propagate.out
index 411748d155..7470c57b5d 100644
--- a/vlib/v/checker/tests/unexpected_or_propagate.out
+++ b/vlib/v/checker/tests/unexpected_or_propagate.out
@@ -1,4 +1,4 @@
-vlib/v/checker/tests/unexpected_or_propagate.vv:6:17: error: unexpected `?`, the function `ret_zero` does not return an optional
+vlib/v/checker/tests/unexpected_or_propagate.vv:6:17: error: unexpected `?`, the function `ret_zero` does neither return an optional nor a result
     4 |
     5 | fn opt_fn() ?int {
     6 |     a := ret_zero()?
diff --git a/vlib/v/fmt/fmt.v b/vlib/v/fmt/fmt.v
index fe35d39191..edc5f07bf3 100644
--- a/vlib/v/fmt/fmt.v
+++ b/vlib/v/fmt/fmt.v
@@ -1335,6 +1335,8 @@ pub fn (mut f Fmt) fn_type_decl(node ast.FnTypeDecl) {
 		f.write(' $ret_str')
 	} else if fn_info.return_type.has_flag(.optional) {
 		f.write(' ?')
+	} else if fn_info.return_type.has_flag(.result) {
+		f.write(' !')
 	}
 
 	f.comments(node.comments, has_nl: false)
@@ -2315,9 +2317,12 @@ pub fn (mut f Fmt) or_expr(node ast.OrExpr) {
 			f.stmts(node.stmts)
 			f.write('}')
 		}
-		.propagate {
+		.propagate_option {
 			f.write(' ?')
 		}
+		.propagate_result {
+			f.write(' !')
+		}
 	}
 }
 
diff --git a/vlib/v/fmt/tests/result_return_type_keep.vv b/vlib/v/fmt/tests/result_return_type_keep.vv
new file mode 100644
index 0000000000..4a88ca2289
--- /dev/null
+++ b/vlib/v/fmt/tests/result_return_type_keep.vv
@@ -0,0 +1,3 @@
+fn foo() !int {
+	return 1
+}
diff --git a/vlib/v/gen/c/assert.v b/vlib/v/gen/c/assert.v
index 0d236f5807..a87d1deb2a 100644
--- a/vlib/v/gen/c/assert.v
+++ b/vlib/v/gen/c/assert.v
@@ -159,7 +159,7 @@ fn (mut g Gen) gen_assert_single_expr(expr ast.Expr, typ ast.Type) {
 			if expr is ast.CTempVar {
 				if expr.orig is ast.CallExpr {
 					should_clone = false
-					if expr.orig.or_block.kind == .propagate {
+					if expr.orig.or_block.kind == .propagate_option {
 						should_clone = true
 					}
 					if expr.orig.is_method && expr.orig.args.len == 0
diff --git a/vlib/v/gen/c/auto_str_methods.v b/vlib/v/gen/c/auto_str_methods.v
index dae5ae955b..62b551e496 100644
--- a/vlib/v/gen/c/auto_str_methods.v
+++ b/vlib/v/gen/c/auto_str_methods.v
@@ -169,7 +169,8 @@ fn (mut g Gen) final_gen_str(typ StrType) {
 	}
 	g.generated_str_fns << typ
 	sym := g.table.sym(typ.typ)
-	if sym.has_method_with_generic_parent('str') && !typ.typ.has_flag(.optional) {
+	if sym.has_method_with_generic_parent('str') && !(typ.typ.has_flag(.optional)
+		|| typ.typ.has_flag(.result)) {
 		return
 	}
 	styp := typ.styp
@@ -178,6 +179,10 @@ fn (mut g Gen) final_gen_str(typ StrType) {
 		g.gen_str_for_option(typ.typ, styp, str_fn_name)
 		return
 	}
+	if typ.typ.has_flag(.result) {
+		g.gen_str_for_result(typ.typ, styp, str_fn_name)
+		return
+	}
 	match sym.info {
 		ast.Alias {
 			if sym.info.is_import {
@@ -258,6 +263,39 @@ fn (mut g Gen) gen_str_for_option(typ ast.Type, styp string, str_fn_name string)
 	g.auto_str_funcs.writeln('}')
 }
 
+fn (mut g Gen) gen_str_for_result(typ ast.Type, styp string, str_fn_name string) {
+	$if trace_autostr ? {
+		eprintln('> gen_str_for_result: $typ.debug() | $styp | $str_fn_name')
+	}
+	parent_type := typ.clear_flag(.result)
+	sym := g.table.sym(parent_type)
+	sym_has_str_method, _, _ := sym.str_method_info()
+	parent_str_fn_name := g.get_str_fn(parent_type)
+
+	g.definitions.writeln('string ${str_fn_name}($styp it); // auto')
+	g.auto_str_funcs.writeln('string ${str_fn_name}($styp it) { return indent_${str_fn_name}(it, 0); }')
+	g.definitions.writeln('string indent_${str_fn_name}($styp it, int indent_count); // auto')
+	g.auto_str_funcs.writeln('string indent_${str_fn_name}($styp it, int indent_count) {')
+	g.auto_str_funcs.writeln('\tstring res;')
+	g.auto_str_funcs.writeln('\tif (!it.is_error) {')
+	if sym.kind == .string {
+		tmp_res := '${parent_str_fn_name}(*($sym.cname*)it.data)'
+		g.auto_str_funcs.writeln('\t\tres = ${str_intp_sq(tmp_res)};')
+	} else if should_use_indent_func(sym.kind) && !sym_has_str_method {
+		g.auto_str_funcs.writeln('\t\tres = indent_${parent_str_fn_name}(*($sym.cname*)it.data, indent_count);')
+	} else {
+		g.auto_str_funcs.writeln('\t\tres = ${parent_str_fn_name}(*($sym.cname*)it.data);')
+	}
+	g.auto_str_funcs.writeln('\t} else {')
+
+	tmp_str := str_intp_sub('error: %%', 'IError_str(it.err)')
+	g.auto_str_funcs.writeln('\t\tres = $tmp_str;')
+	g.auto_str_funcs.writeln('\t}')
+
+	g.auto_str_funcs.writeln('\treturn ${str_intp_sub('result(%%)', 'res')};')
+	g.auto_str_funcs.writeln('}')
+}
+
 fn (mut g Gen) gen_str_for_alias(info ast.Alias, styp string, str_fn_name string) {
 	parent_str_fn_name := g.get_str_fn(info.parent_type)
 	$if trace_autostr ? {
@@ -506,6 +544,8 @@ fn (mut g Gen) fn_decl_str(info ast.FnType) string {
 	fn_str += ')'
 	if info.func.return_type == ast.ovoid_type {
 		fn_str += ' ?'
+	} else if info.func.return_type == ast.rvoid_type {
+		fn_str += ' !'
 	} else if info.func.return_type != ast.void_type {
 		x := util.strip_main_name(g.table.get_type_name(g.unwrap_generic(info.func.return_type)))
 		if info.func.return_type.has_flag(.optional) {
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index a4b20fe684..a03406716c 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -73,7 +73,8 @@ mut:
 	embedded_data             strings.Builder // data to embed in the executable/binary
 	shared_types              strings.Builder // shared/lock types
 	shared_functions          strings.Builder // shared constructors
-	options                   strings.Builder // `Option_xxxx` types
+	options                   strings.Builder // `option_xxxx` types
+	out_results               strings.Builder // `result_xxxx` types
 	json_forward_decls        strings.Builder // json type forward decls
 	sql_buf                   strings.Builder // for writing exprs to args via `sqlite3_bind_int()` etc
 	file                      &ast.File
@@ -100,6 +101,7 @@ mut:
 	is_cc_msvc                bool   // g.pref.ccompiler == 'msvc'
 	vlines_path               string // set to the proper path for generating #line directives
 	optionals                 map[string]string // to avoid duplicates
+	results                   map[string]string // to avoid duplicates
 	done_optionals            shared []string   // to avoid duplicates
 	chan_pop_optionals        map[string]string // types for `x := <-ch or {...}`
 	chan_push_optionals       map[string]string // types for `ch <- x or {...}`
@@ -246,6 +248,7 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 		pcs_declarations: strings.new_builder(100)
 		embedded_data: strings.new_builder(1000)
 		options: strings.new_builder(100)
+		out_results: strings.new_builder(100)
 		shared_types: strings.new_builder(100)
 		shared_functions: strings.new_builder(100)
 		json_forward_decls: strings.new_builder(100)
@@ -319,6 +322,9 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 			for k, v in g.optionals {
 				global_g.optionals[k] = v
 			}
+			for k, v in g.results {
+				global_g.results[k] = v
+			}
 			for k, v in g.as_cast_type_names {
 				global_g.as_cast_type_names[k] = v
 			}
@@ -373,6 +379,7 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 
 	global_g.gen_jsons()
 	global_g.write_optionals()
+	global_g.write_results()
 	global_g.dump_expr_definitions() // this uses global_g.get_str_fn, so it has to go before the below for loop
 	for i := 0; i < global_g.str_types.len; i++ {
 		global_g.final_gen_str(global_g.str_types[i])
@@ -441,6 +448,8 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 	b.write_string(g.shared_types.str())
 	b.writeln('\n// V Option_xxx definitions:')
 	b.write_string(g.options.str())
+	b.writeln('\n// V result_xxx definitions:')
+	b.write_string(g.out_results.str())
 	b.writeln('\n// V json forward decls:')
 	b.write_string(g.json_forward_decls.str())
 	b.writeln('\n// V definitions:')
@@ -535,6 +544,7 @@ fn cgen_process_one_file_cb(p &pool.PoolProcessor, idx int, wid int) &Gen {
 		hotcode_definitions: strings.new_builder(100)
 		embedded_data: strings.new_builder(1000)
 		options: strings.new_builder(100)
+		out_results: strings.new_builder(100)
 		shared_types: strings.new_builder(100)
 		shared_functions: strings.new_builder(100)
 		channel_definitions: strings.new_builder(100)
@@ -595,6 +605,7 @@ pub fn (mut g Gen) free_builders() {
 		g.shared_functions.free()
 		g.channel_definitions.free()
 		g.options.free()
+		g.out_results.free()
 		g.json_forward_decls.free()
 		g.enum_typedefs.free()
 		g.sql_buf.free()
@@ -884,6 +895,8 @@ fn (mut g Gen) typ(t ast.Type) string {
 	if t.has_flag(.optional) {
 		// Register an optional if it's not registered yet
 		return g.register_optional(t)
+	} else if t.has_flag(.result) {
+		return g.register_result(t)
 	} else {
 		return g.base_type(t)
 	}
@@ -965,6 +978,15 @@ fn (mut g Gen) optional_type_name(t ast.Type) (string, string) {
 	return styp, base
 }
 
+fn (mut g Gen) result_type_name(t ast.Type) (string, string) {
+	base := g.base_type(t)
+	mut styp := 'result_$base'
+	if t.is_ptr() {
+		styp = styp.replace('*', '_ptr')
+	}
+	return styp, base
+}
+
 fn (g Gen) optional_type_text(styp string, base string) string {
 	// replace void with something else
 	size := if base == 'void' {
@@ -982,12 +1004,35 @@ fn (g Gen) optional_type_text(styp string, base string) string {
 	return ret
 }
 
+fn (g Gen) result_type_text(styp string, base string) string {
+	// replace void with something else
+	size := if base == 'void' {
+		'u8'
+	} else if base.starts_with('anon_fn') {
+		'void*'
+	} else {
+		base
+	}
+	ret := 'struct $styp {
+	bool is_error;
+	IError err;
+	byte data[sizeof($size) > 0 ? sizeof($size) : 1];
+}'
+	return ret
+}
+
 fn (mut g Gen) register_optional(t ast.Type) string {
 	styp, base := g.optional_type_name(t)
 	g.optionals[base] = styp
 	return styp
 }
 
+fn (mut g Gen) register_result(t ast.Type) string {
+	styp, base := g.result_type_name(t)
+	g.results[base] = styp
+	return styp
+}
+
 fn (mut g Gen) write_optionals() {
 	mut done := []string{}
 	rlock g.done_optionals {
@@ -1003,6 +1048,18 @@ fn (mut g Gen) write_optionals() {
 	}
 }
 
+fn (mut g Gen) write_results() {
+	mut done := []string{}
+	for base, styp in g.results {
+		if base in done {
+			continue
+		}
+		done << base
+		g.typedefs.writeln('typedef struct $styp $styp;')
+		g.out_results.write_string(g.result_type_text(styp, base) + ';\n\n')
+	}
+}
+
 fn (mut g Gen) find_or_register_shared(t ast.Type, base string) string {
 	g.shareds[t.idx()] = base
 	return '__shared__$base'
@@ -1881,6 +1938,10 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 						// Register an optional if it's not registered yet
 						g.register_optional(method.return_type)
 					}
+					if method.return_type.has_flag(.result) {
+						// Register a result if it's not registered yet
+						g.register_result(method.return_type)
+					}
 				}
 			}
 		}
@@ -3893,6 +3954,14 @@ fn (g &Gen) expr_is_multi_return_call(expr ast.Expr) bool {
 	return false
 }
 
+fn (mut g Gen) gen_result_error(target_type ast.Type, expr ast.Expr) {
+	styp := g.typ(target_type)
+	g.write('($styp){ .is_error=true, .err=')
+	g.expr(expr)
+	g.write(', .data={EMPTY_STRUCT_INITIALIZATION} }')
+}
+
+// NB: remove this when optional has no errors anymore
 fn (mut g Gen) gen_optional_error(target_type ast.Type, expr ast.Expr) {
 	styp := g.typ(target_type)
 	g.write('($styp){ .state=2, .err=')
@@ -3921,10 +3990,11 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 	sym := g.table.sym(g.fn_decl.return_type)
 	fn_return_is_multi := sym.kind == .multi_return
 	fn_return_is_optional := g.fn_decl.return_type.has_flag(.optional)
+	fn_return_is_result := g.fn_decl.return_type.has_flag(.result)
 	mut has_semicolon := false
 	if node.exprs.len == 0 {
 		g.write_defer_stmts_when_needed()
-		if fn_return_is_optional {
+		if fn_return_is_optional || fn_return_is_result {
 			styp := g.typ(g.fn_decl.return_type)
 			g.writeln('return ($styp){0};')
 		} else {
@@ -3969,6 +4039,34 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 			return
 		}
 	}
+	// handle promoting error/function returning 'result'
+	if fn_return_is_result {
+		ftyp := g.typ(node.types[0])
+		mut is_regular_result := ftyp == 'result'
+		if is_regular_result || node.types[0] == ast.error_type_idx {
+			if !isnil(g.fn_decl) && g.fn_decl.is_test {
+				test_error_var := g.new_tmp_var()
+				g.write('$ret_typ $test_error_var = ')
+				g.gen_result_error(g.fn_decl.return_type, node.exprs[0])
+				g.writeln(';')
+				g.write_defer_stmts_when_needed()
+				g.gen_failing_return_error_for_test_fn(node, test_error_var)
+				return
+			}
+			if use_tmp_var {
+				g.write('$ret_typ $tmpvar = ')
+			} else {
+				g.write('return ')
+			}
+			g.gen_result_error(g.fn_decl.return_type, node.exprs[0])
+			g.writeln(';')
+			if use_tmp_var {
+				g.write_defer_stmts_when_needed()
+				g.writeln('return $tmpvar;')
+			}
+			return
+		}
+	}
 	// regular cases
 	if fn_return_is_multi && node.exprs.len > 0 && !g.expr_is_multi_return_call(node.exprs[0]) {
 		if node.exprs.len == 1 && (node.exprs[0] is ast.IfExpr || node.exprs[0] is ast.MatchExpr) {
@@ -3983,7 +4081,7 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 		typ_sym := g.table.sym(g.fn_decl.return_type)
 		mr_info := typ_sym.info as ast.MultiReturn
 		mut styp := ''
-		if fn_return_is_optional {
+		if fn_return_is_optional || fn_return_is_result {
 			g.writeln('$ret_typ $tmpvar;')
 			styp = g.base_type(g.fn_decl.return_type)
 			g.write('opt_ok(&($styp/*X*/[]) { ')
@@ -4054,7 +4152,7 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 			}
 		}
 		g.write('}')
-		if fn_return_is_optional {
+		if fn_return_is_optional || fn_return_is_result {
 			g.writeln(' }, (Option*)(&$tmpvar), sizeof($styp));')
 			g.write_defer_stmts_when_needed()
 			g.write('return $tmpvar')
@@ -4063,7 +4161,7 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 		if multi_unpack.len > 0 {
 			g.insert_before_stmt(multi_unpack)
 		}
-		if use_tmp_var && !fn_return_is_optional {
+		if use_tmp_var && !fn_return_is_optional && !fn_return_is_result {
 			if !has_semicolon {
 				g.writeln(';')
 			}
@@ -4109,6 +4207,35 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 			g.writeln('return $tmpvar;')
 			return
 		}
+		expr_type_is_result := match expr0 {
+			ast.CallExpr {
+				expr0.return_type.has_flag(.result) && expr0.or_block.kind == .absent
+			}
+			else {
+				node.types[0].has_flag(.result)
+			}
+		}
+		if fn_return_is_result && !expr_type_is_result && return_sym.name != 'result' {
+			styp := g.base_type(g.fn_decl.return_type)
+			g.writeln('$ret_typ $tmpvar;')
+			g.write('result_ok(&($styp[]) { ')
+			if !g.fn_decl.return_type.is_ptr() && node.types[0].is_ptr() {
+				if !(node.exprs[0] is ast.Ident && !g.is_amp) {
+					g.write('*')
+				}
+			}
+			for i, expr in node.exprs {
+				g.expr_with_cast(expr, node.types[i], g.fn_decl.return_type.clear_flag(.result))
+				if i < node.exprs.len - 1 {
+					g.write(', ')
+				}
+			}
+			g.writeln(' }, (result*)(&$tmpvar), sizeof($styp));')
+			g.write_defer_stmts_when_needed()
+			g.autofree_scope_vars(node.pos.pos - 1, node.pos.line_nr, true)
+			g.writeln('return $tmpvar;')
+			return
+		}
 		// autofree before `return`
 		// set free_parent_scopes to true, since all variables defined in parent
 		// scopes need to be freed before the return
@@ -4596,7 +4723,7 @@ fn (mut g Gen) write_init_function() {
 }
 
 const (
-	builtins = ['string', 'array', 'DenseArray', 'map', 'Error', 'IError', 'Option']
+	builtins = ['string', 'array', 'DenseArray', 'map', 'Error', 'IError', 'Option', 'result']
 )
 
 fn (mut g Gen) write_builtin_types() {
@@ -4933,7 +5060,11 @@ fn (mut g Gen) or_block(var_name string, or_block ast.OrExpr, return_type ast.Ty
 		if return_type != 0 && g.table.sym(return_type).kind == .function {
 			mr_styp = 'voidptr'
 		}
-		g.writeln('if (${cvar_name}.state != 0) { /*or block*/ ')
+		if return_type.has_flag(.result) {
+			g.writeln('if (${cvar_name}.is_error) { /*or block*/ ')
+		} else {
+			g.writeln('if (${cvar_name}.state != 0) { /*or block*/ ')
+		}
 	}
 	if or_block.kind == .block {
 		g.or_expr_return_type = return_type.clear_flag(.optional)
@@ -4975,7 +5106,7 @@ fn (mut g Gen) or_block(var_name string, or_block ast.OrExpr, return_type ast.Ty
 			}
 		}
 		g.or_expr_return_type = ast.void_type
-	} else if or_block.kind == .propagate {
+	} else if or_block.kind == .propagate_option {
 		if g.file.mod.name == 'main' && (isnil(g.fn_decl) || g.fn_decl.is_main) {
 			// In main(), an `opt()?` call is sugar for `opt() or { panic(err) }`
 			err_msg := 'IError_name_table[${cvar_name}.err._typ]._method_msg(${cvar_name}.err._object)'
@@ -5004,6 +5135,35 @@ fn (mut g Gen) or_block(var_name string, or_block ast.OrExpr, return_type ast.Ty
 				g.writeln('\treturn $err_obj;')
 			}
 		}
+	} else if or_block.kind == .propagate_result {
+		if g.file.mod.name == 'main' && (isnil(g.fn_decl) || g.fn_decl.is_main) {
+			// In main(), an `opt()!` call is sugar for `opt() or { panic(err) }`
+			err_msg := 'IError_name_table[${cvar_name}.err._typ]._method_msg(${cvar_name}.err._object)'
+			if g.pref.is_debug {
+				paline, pafile, pamod, pafn := g.panic_debug_info(or_block.pos)
+				g.writeln('panic_debug($paline, tos3("$pafile"), tos3("$pamod"), tos3("$pafn"), $err_msg);')
+			} else {
+				g.writeln('\tpanic_result_not_set($err_msg);')
+			}
+		} else if !isnil(g.fn_decl) && g.fn_decl.is_test {
+			g.gen_failing_error_propagation_for_test_fn(or_block, cvar_name)
+		} else {
+			// In ordinary functions, `opt()!` call is sugar for:
+			// `opt() or { return err }`
+			// Since we *do* return, first we have to ensure that
+			// the defered statements are generated.
+			g.write_defer_stmts()
+			// Now that option types are distinct we need a cast here
+			if g.fn_decl.return_type == ast.void_type {
+				g.writeln('\treturn;')
+			} else {
+				styp := g.typ(g.fn_decl.return_type)
+				err_obj := g.new_tmp_var()
+				g.writeln('\t$styp $err_obj;')
+				g.writeln('\tmemcpy(&$err_obj, &$cvar_name, sizeof(result));')
+				g.writeln('\treturn $err_obj;')
+			}
+		}
 	}
 	g.writeln('}')
 	g.set_current_pos_as_last_stmt_pos()
diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index 5656307564..ffb66eeaa8 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -671,9 +671,6 @@ fn (mut g Gen) call_expr(node ast.CallExpr) {
 	tmp_opt := if gen_or || gen_keep_alive { g.new_tmp_var() } else { '' }
 	if gen_or || gen_keep_alive {
 		mut ret_typ := node.return_type
-		if gen_or {
-			ret_typ = ret_typ.set_flag(.optional)
-		}
 		styp := g.typ(ret_typ)
 		if gen_or && !is_gen_or_and_assign_rhs {
 			cur_line = g.go_before_stmt(0)
@@ -695,7 +692,7 @@ fn (mut g Gen) call_expr(node ast.CallExpr) {
 		// if !g.is_autofree {
 		g.or_block(tmp_opt, node.or_block, node.return_type)
 		//}
-		unwrapped_typ := node.return_type.clear_flag(.optional)
+		unwrapped_typ := node.return_type.clear_flag(.optional).clear_flag(.result)
 		unwrapped_styp := g.typ(unwrapped_typ)
 		if unwrapped_typ == ast.void_type {
 			g.write('\n $cur_line')
diff --git a/vlib/v/gen/c/str_intp.v b/vlib/v/gen/c/str_intp.v
index 663fe05bd1..9544a56ec4 100644
--- a/vlib/v/gen/c/str_intp.v
+++ b/vlib/v/gen/c/str_intp.v
@@ -17,13 +17,14 @@ fn (mut g Gen) str_format(node ast.StringInterLiteral, i int) (u64, string) {
 	mut upper_case := false // set upercase for the result string
 	mut typ := g.unwrap_generic(node.expr_types[i])
 	sym := g.table.sym(typ)
+
 	if sym.kind == .alias {
 		typ = (sym.info as ast.Alias).parent_type
 	}
 	mut remove_tail_zeros := false
 	fspec := node.fmts[i]
 	mut fmt_type := StrIntpType{}
-
+	g.write('/*$fspec $sym*/')
 	// upper cases
 	if (fspec - `A`) <= (`Z` - `A`) {
 		upper_case = true
diff --git a/vlib/v/gen/js/auto_str_methods.v b/vlib/v/gen/js/auto_str_methods.v
index 2374936e8c..f90b24ed4a 100644
--- a/vlib/v/gen/js/auto_str_methods.v
+++ b/vlib/v/gen/js/auto_str_methods.v
@@ -413,6 +413,8 @@ fn (mut g JsGen) fn_decl_str(info ast.FnType) string {
 	fn_str += ')'
 	if info.func.return_type == ast.ovoid_type {
 		fn_str += ' ?'
+	} else if info.func.return_type == ast.rvoid_type {
+		fn_str += ' !'
 	} else if info.func.return_type != ast.void_type {
 		x := util.strip_main_name(g.table.get_type_name(g.unwrap_generic(info.func.return_type)))
 		if info.func.return_type.has_flag(.optional) {
diff --git a/vlib/v/gen/js/fn.v b/vlib/v/gen/js/fn.v
index e82724ebb7..0fde781856 100644
--- a/vlib/v/gen/js/fn.v
+++ b/vlib/v/gen/js/fn.v
@@ -116,7 +116,7 @@ fn (mut g JsGen) js_call(node ast.CallExpr) {
 				// g.write('return ')
 				g.stmt(it.or_block.stmts.last())
 			}
-			.propagate {
+			.propagate_option {
 				panicstr := '`optional not set (\${err + ""})`'
 				if g.file.mod.name == 'main' && g.fn_decl.name == 'main.main' {
 					g.writeln('return builtin__panic($panicstr)')
@@ -176,12 +176,12 @@ fn (mut g JsGen) js_method_call(node ast.CallExpr) {
 				// g.write('return ')
 				g.stmt(it.or_block.stmts.last())
 			}
-			.propagate {
+			.propagate_option {
 				panicstr := '`optional not set (\${err + ""})`'
 				if g.file.mod.name == 'main' && g.fn_decl.name == 'main.main' {
 					g.writeln('return builtin__panic($panicstr)')
 				} else {
-					g.writeln('throw new Option({ state: new u8(2), err: error(new string($panicstr)) });')
+					g.writeln('throw new option({ state: new u8(2), err: error(new string($panicstr)) });')
 				}
 			}
 			else {}
@@ -367,7 +367,7 @@ fn (mut g JsGen) method_call(node ast.CallExpr) {
 				// g.write('return ')
 				g.stmt(it.or_block.stmts.last())
 			}
-			.propagate {
+			.propagate_option {
 				panicstr := '`optional not set (\${err.valueOf().msg})`'
 				if g.file.mod.name == 'main' && g.fn_decl.name == 'main.main' {
 					g.writeln('return builtin__panic($panicstr)')
@@ -468,7 +468,7 @@ fn (mut g JsGen) gen_call_expr(it ast.CallExpr) {
 				//	g.write('return ')
 				g.stmt(it.or_block.stmts.last())
 			}
-			.propagate {
+			.propagate_option {
 				panicstr := '`optional not set (\${err.valueOf().msg})`'
 				if g.file.mod.name == 'main' && g.fn_decl.name == 'main.main' {
 					g.writeln('return builtin__panic($panicstr)')
diff --git a/vlib/v/gen/js/js.v b/vlib/v/gen/js/js.v
index 364181c206..02e660cd86 100644
--- a/vlib/v/gen/js/js.v
+++ b/vlib/v/gen/js/js.v
@@ -1183,7 +1183,7 @@ fn (mut g JsGen) gen_assert_single_expr(expr ast.Expr, typ ast.Type) {
 			if expr is ast.CTempVar {
 				if expr.orig is ast.CallExpr {
 					should_clone = false
-					if expr.orig.or_block.kind == .propagate {
+					if expr.orig.or_block.kind == .propagate_option {
 						should_clone = true
 					}
 					if expr.orig.is_method && expr.orig.args.len == 0
diff --git a/vlib/v/parser/expr.v b/vlib/v/parser/expr.v
index 41cac7f6d1..fc18f0cb5c 100644
--- a/vlib/v/parser/expr.v
+++ b/vlib/v/parser/expr.v
@@ -535,7 +535,7 @@ fn (mut p Parser) infix_expr(left ast.Expr) ast.Expr {
 		}
 		if p.tok.kind == .question {
 			p.next()
-			or_kind = .propagate
+			or_kind = .propagate_option
 		}
 		p.or_is_handled = false
 	}
@@ -627,7 +627,7 @@ fn (mut p Parser) prefix_expr() ast.Expr {
 		}
 		if p.tok.kind == .question {
 			p.next()
-			or_kind = .propagate
+			or_kind = .propagate_option
 		}
 		p.or_is_handled = false
 	}
diff --git a/vlib/v/parser/fn.v b/vlib/v/parser/fn.v
index 5b36633900..09b68a1bd5 100644
--- a/vlib/v/parser/fn.v
+++ b/vlib/v/parser/fn.v
@@ -45,10 +45,6 @@ pub fn (mut p Parser) call_expr(language ast.Language, mod string) ast.CallExpr
 	args := p.call_args()
 	last_pos := p.tok.pos()
 	p.check(.rpar)
-	// ! in mutable methods
-	if p.tok.kind == .not {
-		p.next()
-	}
 	mut pos := first_pos.extend(last_pos)
 	mut or_stmts := []ast.Stmt{} // TODO remove unnecessary allocations by just using .absent
 	mut or_pos := p.tok.pos()
@@ -70,13 +66,14 @@ pub fn (mut p Parser) call_expr(language ast.Language, mod string) ast.CallExpr
 		p.close_scope()
 		p.inside_or_expr = was_inside_or_expr
 	}
-	if p.tok.kind == .question {
+	if p.tok.kind in [.question, .not] {
+		is_not := p.tok.kind == .not
 		// `foo()?`
 		p.next()
 		if p.inside_defer {
 			p.error_with_pos('error propagation not allowed inside `defer` blocks', p.prev_tok.pos())
 		}
-		or_kind = .propagate
+		or_kind = if is_not { .propagate_result } else { .propagate_option }
 	}
 	if fn_name in p.imported_symbols {
 		fn_name = p.imported_symbols[fn_name]
diff --git a/vlib/v/parser/parse_type.v b/vlib/v/parser/parse_type.v
index ce29321e1c..5076a67736 100644
--- a/vlib/v/parser/parse_type.v
+++ b/vlib/v/parser/parse_type.v
@@ -375,18 +375,24 @@ pub fn (mut p Parser) parse_sum_type_variants() []ast.TypeNode {
 pub fn (mut p Parser) parse_type() ast.Type {
 	// optional
 	mut is_optional := false
+	mut is_result := false
+	line_nr := p.tok.line_nr
 	optional_pos := p.tok.pos()
 	if p.tok.kind == .question {
-		line_nr := p.tok.line_nr
 		p.next()
 		is_optional = true
-		if p.tok.line_nr > line_nr {
-			mut typ := ast.void_type
-			if is_optional {
-				typ = typ.set_flag(.optional)
-			}
-			return typ
+	} else if p.tok.kind == .not {
+		p.next()
+		is_result = true
+	}
+	if (is_optional || is_result) && p.tok.line_nr > line_nr {
+		mut typ := ast.void_type
+		if is_optional {
+			typ = typ.set_flag(.optional)
+		} else if is_result {
+			typ = typ.set_flag(.result)
 		}
+		return typ
 	}
 	is_shared := p.tok.kind == .key_shared
 	is_atomic := p.tok.kind == .key_atomic
@@ -441,6 +447,9 @@ pub fn (mut p Parser) parse_type() ast.Type {
 	if is_optional {
 		typ = typ.set_flag(.optional)
 	}
+	if is_result {
+		typ = typ.set_flag(.result)
+	}
 	if is_shared {
 		typ = typ.set_flag(.shared_f)
 	}
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index f0fade2121..d07b67d9ac 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -2478,7 +2478,7 @@ fn (mut p Parser) index_expr(left ast.Expr, is_gated bool) ast.IndexExpr {
 			// `a[start..end] ?`
 			if p.tok.kind == .question {
 				or_pos_high = p.tok.pos()
-				or_kind_high = .propagate
+				or_kind_high = .propagate_option
 				p.next()
 			}
 		}
@@ -2552,7 +2552,7 @@ fn (mut p Parser) index_expr(left ast.Expr, is_gated bool) ast.IndexExpr {
 			// `a[start..end] ?`
 			if p.tok.kind == .question {
 				or_pos_low = p.tok.pos()
-				or_kind_low = .propagate
+				or_kind_low = .propagate_option
 				p.next()
 			}
 		}
@@ -2609,7 +2609,7 @@ fn (mut p Parser) index_expr(left ast.Expr, is_gated bool) ast.IndexExpr {
 		// `a[i] ?`
 		if p.tok.kind == .question {
 			or_pos = p.tok.pos()
-			or_kind = .propagate
+			or_kind = .propagate_option
 			p.next()
 		}
 	}
@@ -2711,15 +2711,15 @@ fn (mut p Parser) dot_expr(left ast.Expr) ast.Expr {
 			p.inside_or_expr = was_inside_or_expr
 		}
 		// `foo()?`
-		if p.tok.kind == .question {
+		if p.tok.kind in [.question, .not] {
+			is_not := p.tok.kind == .not
 			p.next()
 			if p.inside_defer {
 				p.error_with_pos('error propagation not allowed inside `defer` blocks',
 					p.prev_tok.pos())
 			}
-			or_kind = .propagate
+			or_kind = if is_not { .propagate_result } else { .propagate_option }
 		}
-		//
 		end_pos := p.prev_tok.pos()
 		pos := name_pos.extend(end_pos)
 		comments := p.eat_comments(same_line: true)
diff --git a/vlib/v/parser/tests/option_result_err.out b/vlib/v/parser/tests/option_result_err.out
new file mode 100644
index 0000000000..7d83b67384
--- /dev/null
+++ b/vlib/v/parser/tests/option_result_err.out
@@ -0,0 +1,5 @@
+vlib/v/parser/tests/option_result_err.vv:2:2: error: invalid expression: unexpected keyword `return`
+    1 | fn abc() ?!string {
+    2 |     return ''
+      |     ~~~~~~
+    3 | }
diff --git a/vlib/v/parser/tests/option_result_err.vv b/vlib/v/parser/tests/option_result_err.vv
new file mode 100644
index 0000000000..e36c0b19c5
--- /dev/null
+++ b/vlib/v/parser/tests/option_result_err.vv
@@ -0,0 +1,3 @@
+fn abc() ?!string {
+	return ''
+}
diff --git a/vlib/v/parser/tests/result_option_err.out b/vlib/v/parser/tests/result_option_err.out
new file mode 100644
index 0000000000..4375d046a3
--- /dev/null
+++ b/vlib/v/parser/tests/result_option_err.out
@@ -0,0 +1,5 @@
+vlib/v/parser/tests/result_option_err.vv:2:2: error: invalid expression: unexpected keyword `return`
+    1 | fn abc() ?!string {
+    2 |     return ''
+      |     ~~~~~~
+    3 | }
diff --git a/vlib/v/parser/tests/result_option_err.vv b/vlib/v/parser/tests/result_option_err.vv
new file mode 100644
index 0000000000..e36c0b19c5
--- /dev/null
+++ b/vlib/v/parser/tests/result_option_err.vv
@@ -0,0 +1,3 @@
+fn abc() ?!string {
+	return ''
+}
diff --git a/vlib/v/scanner/scanner.v b/vlib/v/scanner/scanner.v
index 2f764b1840..36733e8962 100644
--- a/vlib/v/scanner/scanner.v
+++ b/vlib/v/scanner/scanner.v
@@ -1023,7 +1023,7 @@ fn (mut s Scanner) text_scan() token.Token {
 					s.pos += 2
 					return s.new_token(.not_is, '', 3)
 				} else {
-					return s.new_token(.not, '', 1)
+					return s.new_token(.not, '!', 1)
 				}
 			}
 			`~` {
diff --git a/vlib/v/tests/results_test.v b/vlib/v/tests/results_test.v
new file mode 100644
index 0000000000..ab4c047987
--- /dev/null
+++ b/vlib/v/tests/results_test.v
@@ -0,0 +1,65 @@
+fn foo() !int {
+	return 1
+}
+
+fn test_return_int() {
+	x := foo() or { 0 }
+	assert x == 1
+}
+
+fn foo_err() !int {
+	return error('throw')
+}
+
+fn test_return_err() {
+	x := foo_err() or { 0 }
+	assert x == 0
+}
+
+fn test_return_err_var() {
+	foo_err() or { assert err.msg() == 'throw' }
+}
+
+fn test_str() {
+	assert '$foo()' == 'result(1)'
+}
+
+fn result_void(err bool) ! {
+	if err {
+		return error('throw')
+	}
+}
+
+fn test_result_void() {
+	result_void(false) or { assert false }
+}
+
+fn test_result_void_err() {
+	mut or_block := false
+	result_void(true) or {
+		assert err.msg() == 'throw'
+		or_block = true
+	}
+	assert or_block
+}
+
+fn propagate() ! {
+	result_void(false) !
+}
+
+fn test_propagation() {
+	propagate() or { assert false }
+}
+
+fn function_that_can_return_error() !int {
+	return error('abc')
+}
+
+fn util_error_propagation() ! {
+	function_that_can_return_error() !
+	assert false
+}
+
+fn test_return_on_error_propagation() {
+	util_error_propagation() or { assert err.msg() == 'abc' }
+}
diff --git a/vlib/v/token/token.v b/vlib/v/token/token.v
index 2325f0b9aa..dda124058e 100644
--- a/vlib/v/token/token.v
+++ b/vlib/v/token/token.v
@@ -479,7 +479,7 @@ pub fn (tok Kind) is_relational() bool {
 
 [inline]
 pub fn (k Kind) is_start_of_type() bool {
-	return k in [.name, .lpar, .amp, .lsbr, .question, .key_shared]
+	return k in [.name, .lpar, .amp, .lsbr, .question, .key_shared, .not]
 }
 
 [inline]