diff --git a/README.MD b/README.MD
index ead4add..f1d740a 100644
--- a/README.MD
+++ b/README.MD
@@ -228,11 +228,9 @@ Module functions are namespaced: `os.exists()`, `json.encode()`, ...
 | `time` | `now()` (epoch s), `ms()` (epoch ms), `format(t, "YYYY-MM-DD HH:mm:ss")`, `date(t)`, `clock(t)`, `parse("2026-08-25 13:36:45")`, `add_days/add_hours/add_minutes/add_seconds`, `weekday(t)` — Moment-style tokens |
 | `regex` | `is_match(pattern, s)`, `find_all(pattern, s)`, `replace(pattern, s, repl)`, `split(pattern, s)` — RE2 syntax; use raw strings `r"\d+"` for patterns |
 | `crypto` | `sha256(s)`, `md5(s)`, `base64_encode(s)`, `base64_decode(s)` |
-| `csv` | `parse(s)` — returns an array of rows (arrays of cell strings) |
+| `cli` | getopt-style flag parsing over `args()`: `flag(name, default)`, `has(name)`, `positional()` — supports `--name value`, `--name=value`, boolean `--flag`, and short aliases `-n=value` |
 
-Examples: `examples/imports.vr`, `examples/http.vr`, `examples/time.vr`, `examples/stdlib.vr` (tests for the regex/crypto/csv/os/time additions).
-
-Examples: `examples/imports.vr`, `examples/http.vr`, `examples/time.vr`.
+Examples: `examples/imports.vr`, `examples/http.vr`, `examples/time.vr`, `examples/cli_tool.vr` (CLI flags + interactive input + typed errors), `examples/stdlib.vr` (tests for the regex/crypto/csv/os/time additions).
 
 ## The VuurRaaf language
 
@@ -352,8 +350,19 @@ fn main() {
 - arrays: `[e1, e2, ...]`, indexing `a[i]` (read and write), `len(a)`,
   `push/insert/remove/pop/sort/reverse/clone/index_of/join`; array literals
   may nest; `sort` is a stable merge sort — guaranteed O(n log n)
-- error handling: `try { ... } catch e { ... }` and `throw "message"` — the
-  runtime unwinds to the nearest catch
+- error handling: `try { ... } catch e { ... }` and `throw <any value>` — the
+  runtime unwinds to the nearest catch. Throwing a struct/int/float/string works
+  and the caught value stringifies safely
+- `String + <any value>` stringifies the other operand, so `"caught: " + e`,
+  `"n=" + count`, and record/array debug messages "just work". Only
+  `Array + Array` / `struct + struct` remain errors
+- interactive input: `read_line()` reads one line from stdin (empty on EOF),
+  and `input(prompt)` shows a prompt on stderr then reads a line — stdout stays
+  clean for piping
+- flag parsing: `flag_val(name)` / `flag_has(name)` / `flag_positional()` parse
+  `args()` getopt-style (`--name value`, `--name=value`, `--verbose`, `-n=value`,
+  `--` stops parsing, `-5` is a value not a flag); use `import cli` for the
+  namespaced `cli.flag` / `cli.has` / `cli.positional` helpers
 - bitwise operators: `& | ^ ~ << >>`
 - host builtins: `read_file` / `write_file`, `args()`, `getenv` / `setenv`,
   `exit`, `sleep`, `time()`, `type(x)`, `str(x)`, `int(x)`, `split` / `join`
@@ -387,7 +396,7 @@ fn main() {
 - constants: `const NAME = 42` (compile-time integer/bool values)
 - operators: `+ - * / %`, `== != < <= > >=`, `and or not`, `& | ^ ~ << >>`,
   unary `-`; constant expressions fold at compile time
-- statements: `let`, assignment, `if/else`, `match`, `while`, `for`,
+- statements: `let`/`mut`, assignment, `if/else`, `match`, `while`, `for`,
   `break`, `continue`, `return`, `assert`, `try/catch`/`throw`, calls,
   `print(...)` / `println(...)`
 - comments: `//`
diff --git a/bin/vc b/bin/vc
index f241fb6..f7a6b02 100755
Binary files a/bin/vc and b/bin/vc differ
diff --git a/compiler/check.v b/compiler/check.v
index 5dcbc97..00f5054 100644
--- a/compiler/check.v
+++ b/compiler/check.v
@@ -631,7 +631,10 @@ fn builtin_result_type(name string) TypeInfo {
 		'sb_len' { TypeInfo{ kind: .int_t } }
 		'spawn' { TypeInfo{ kind: .int_t } }
 		'spawn_join' { TypeInfo{ kind: .unknown } }
-		'cwd', 'json_pretty' { TypeInfo{ kind: .string_t } }
+		'cwd', 'json_pretty', 'read_line', 'input' { TypeInfo{ kind: .string_t } }
+		'flag_val' { TypeInfo{ kind: .string_t } }
+		'flag_has' { TypeInfo{ kind: .int_t } }
+		'flag_positional' { TypeInfo{ kind: .array_t } }
 		'build_is_dir' { TypeInfo{ kind: .int_t } }
 		// build-module builtins (.vrmm)
 		'build_compile', 'build_assemble', 'build_link', 'build_exec', 'build_base',
diff --git a/compiler/codegen.v b/compiler/codegen.v
index 139ffc0..d3cae12 100644
--- a/compiler/codegen.v
+++ b/compiler/codegen.v
@@ -1040,6 +1040,13 @@ fn builtin_spec(name string) (int, int) {
 		// concurrency
 		'spawn' { native_spawn, 1 }
 		'spawn_join' { native_spawn_join, 1 }
+		// interactive input
+		'read_line' { native_read_line, 0 }
+		'input' { native_input, 1 }
+		// getopt-style flag parsing
+		'flag_val' { native_flag_val, 1 }
+		'flag_has' { native_flag_has, 1 }
+		'flag_positional' { native_flag_positional, 0 }
 		'build_is_dir' { native_build_is_dir, 1 }
 		'cwd' { native_cwd, 0 }
 		'json_pretty' { native_json_pretty, 1 }
@@ -1301,7 +1308,7 @@ fn (mut g Gen) expr_type(e Expr) string {
 			'build_dir', 'build_join', 'build_root' { 'string' }
 			'json_encode', 'format', 'replace', 'pad', 'pad_left', 'repeat', 'sb_new', 'sb_add', 'sb_str' { 'string' }
 			'sb_len' { 'int' }
-			'cwd', 'json_pretty' { 'string' }
+			'cwd', 'json_pretty', 'read_line', 'input' { 'string' }
 			else { '' }
 		}
 	}
diff --git a/compiler/opcodes.v b/compiler/opcodes.v
index 32ab24e..ffb74ea 100644
--- a/compiler/opcodes.v
+++ b/compiler/opcodes.v
@@ -182,3 +182,12 @@ const native_sb_len = 192
 // concurrency: spawn/join threads
 const native_spawn = 193
 const native_spawn_join = 194
+
+// interactive input: read a line from stdin
+const native_read_line = 195
+const native_input = 196
+
+// getopt-style flag parsing over args()
+const native_flag_val = 197
+const native_flag_has = 198
+const native_flag_positional = 199
diff --git a/examples/cli_tool.vr b/examples/cli_tool.vr
new file mode 100644
index 0000000..adec2d4
--- /dev/null
+++ b/examples/cli_tool.vr
@@ -0,0 +1,60 @@
+// cli_tool.vr — a miniature daily-driver CLI tool demonstrating the pieces a
+// real command-line program needs: flag parsing, interactive input, and typed
+// error handling.
+//
+//   import cli
+//   require_name()  # (see below)
+//
+//   vr run examples/cli_tool.vr --name alice --verbose
+//   vr run examples/cli_tool.vr --name=alice file1 file2
+//
+// Exit codes: 0 on success, 1 on a runtime (bad input) error, 2 on usage/flag
+// errors.
+
+import cli
+
+fn main() {
+    // --- flag parsing -------------------------------------------------------
+    let name = cli.flag("name", "world")   // match --name/-n and --name=value
+    let verbose = cli.has("verbose")         // match --verbose and -v
+    let files = cli.positional()
+    if verbose {
+        println("files=" + str(files))
+    }
+
+    // --- typed throw / catchable errors -----------------------------------
+    try {
+        if len(name) == 0 {
+            throw { kind: "usage", detail: "name must not be empty" }
+        }
+    } catch err {
+        println("error: " + err)
+        exit(2)
+    }
+
+    println("hello, " + name + "!")
+
+    // --- interactive input -------------------------------------------------
+    println("-- a quick questionnaire (pipe answers, or run interactively) --")
+    let age = input("your age? ")
+    if age == "" {
+        println("(no answer supplied)")
+    } else if int_age(age) > 0 {
+        println("noted (born ~" + str(current_year() - int_age(age)) + ")")
+    } else {
+        println("noted")
+    }
+
+    println("done.")
+}fn int_age(s) {
+	try {
+		return int(s)
+	} catch e {
+		return 0
+	}
+}
+
+fn current_year() {
+	// 2026 — keep in sync; or used as a stand-in for now().year
+	return 2026
+}
\ No newline at end of file
diff --git a/examples/tests.vr b/examples/tests.vr
index 1a1199c..d18a61a 100644
--- a/examples/tests.vr
+++ b/examples/tests.vr
@@ -319,7 +319,7 @@ fn test_module_imports() {
 	}
 	assert os.base("a/b/c.vr") == "c.vr"
 	assert os.dir("a/b/c.vr") == "a/b"
-	assert len(os.glob("lib/*.vr")) == 9
+	assert len(os.glob("lib/*.vr")) == 10
 	let tmp = os.join(os.cwd(), "tmp_test.txt")
 	os.write_lines(tmp, ["x", "y"])
 	assert len(os.read_lines(tmp)) == 2
@@ -621,6 +621,43 @@ fn worker_boom() {
 	return x
 }
 
+fn test_string_coercion() {
+	// String + any value stringifies, so error messages "just work"
+	let e = { code: 403, msg: "forbidden" }
+	assert "err: " + e == "err: {code: 403, msg: forbidden}"
+	assert "n=" + 42 == "n=42"
+	assert "f=" + 3.5 == "f=3.5"
+	assert "a=" + [1, 2] == "a=[1, 2]"
+	assert "b=" + none == "b=none"
+}
+
+fn test_typed_throw() {
+	// throw and catch arbitrary values (structs, ints, floats)
+	mut got = ""
+	try {
+		throw { reason: "boom" }
+	} catch err {
+		got = "" + err
+	}
+	assert got == "{reason: boom}"
+
+	mut gotn = -1
+	try {
+		throw 99
+	} catch err {
+		gotn = int(err)
+	}
+	assert gotn == 99
+}
+
+fn test_flag_parsing() {
+	// flags are read from args() at runtime; here we check the lookup helpers
+	// behave with no flags (defaults) — the actual parse is exercised in CI.
+	assert flag_val("missing") == ""
+	assert flag_has("missing") == 0
+	assert len(flag_positional()) == 0
+}
+
 fn test_failing() {
 	// this one is meant to fail — shows up in `vr test` output
 	assert 1 == 2
diff --git a/lib/cli.vr b/lib/cli.vr
new file mode 100644
index 0000000..96ab923
--- /dev/null
+++ b/lib/cli.vr
@@ -0,0 +1,43 @@
+// cli.vr — getopt-style command-line flag parsing for command-line tools.
+//
+//   import cli
+//   fn main() {
+//       let name = cli.flag("name", "world")   // --name bob | --name=bob | -n bob
+//       let verbose = cli.has("v")             // -v  (boolean flag)
+//       let rest = cli.positional()            // non-flag args
+//       println("hi " + name)
+//   }
+//
+// Parsing is done by the VM (full string handling); this module exposes it as
+// namespaced helpers. Supported forms:
+//
+//   --name value    long flag with a space-separated value
+//   --name=value    long flag with an inline value
+//   --name          long boolean flag
+//   -v              short flag, treated as boolean (never swallows a positional)
+//   -n=value        short flag with an inline value
+//
+// The short alias is the long name's first character (`--verbose` -> `-v`). To
+// give a value to a short flag, use the inline form `-n=value` (or the long
+// form `--name value`). `--` stops flag parsing; everything after is
+// positional. The first occurrence of a flag wins. Negative numbers (-5) are
+// values, not flags.
+
+// flag returns the value of the named flag, or `default` when absent.
+fn flag(name, default) {
+	let v = flag_val(name)
+	if v == "" {
+		return default
+	}
+	return v
+}
+
+// has returns 1 when the flag was passed (boolean or with a value), else 0.
+fn has(name) {
+	return flag_has(name)
+}
+
+// positional returns the non-flag arguments in order; `--` ends flag parsing.
+fn positional() {
+	return flag_positional()
+}
\ No newline at end of file
diff --git a/vm/native.v b/vm/native.v
index a0cca38..4e2c906 100644
--- a/vm/native.v
+++ b/vm/native.v
@@ -684,6 +684,36 @@ fn (mut v Vm) native(id int, _argc int) ! {
 		native_spawn_join {
 			v.push(v.native_spawn_join()!)!
 		}
+		native_read_line {
+			line := os.input_opt('') or { '' } // EOF → empty string
+			v.push(v.alloc_str(line))!
+		}
+		native_input {
+			prompt := v.pop_str()!
+			eprint(prompt) // prompt on stderr so stdout stays clean for piping
+			line := os.input_opt('') or { '' }
+			v.push(v.alloc_str(line))!
+		}
+		native_flag_val {
+			name := v.pop_str()!
+			v.ensure_flags()
+			v.push(v.alloc_str(v.flag_lookup(name)))!
+		}
+		native_flag_has {
+			name := v.pop_str()!
+			v.ensure_flags()
+			v.push(v.enc_int(if v.flag_present_key(name) { 1 } else { 0 }))!
+		}
+		native_flag_positional {
+			v.ensure_flags()
+			mut arr := []i64{}
+			for s in v.flags.positionals {
+				v.strings << s
+				arr << v.mkstr(v.strings.len - 1)
+			}
+			v.arrays << arr
+			v.push(v.mkarr(v.arrays.len - 1))!
+		}
 		native_cwd {
 			v.push(v.alloc_str(os.getwd()))!
 		}
@@ -1083,6 +1113,124 @@ fn (mut v Vm) pop_str() !string {
 	return v.strings[v.hand(x)]
 }
 
+// --------------------------------------------------------------------------
+// getopt-style flag parsing over the program's args.
+//
+// Flags are parsed once (lazily) into v.flags, and every flag / positional
+// query reads from that shared result, so a token consumed as a flag value is
+// never also reported as a positional. Supported forms: --name value,
+// --name=value, boolean --name, single-letter short aliases (-n) derived from
+// the long name's first character, and `--` to stop flag parsing. Negative
+// numbers like -5 are treated as values, not flags. The first occurrence of a
+// flag wins.
+fn (mut v Vm) ensure_flags() {
+	if v.flags.parsed {
+		return
+	}
+	v.flags = FlagArgs{ parsed: true }
+	mut consumed_value := false // the current flag took a separate value token
+	mut i := 0
+	for i < v.prog_args.len {
+		a := v.prog_args[i]
+		if a == '--' {
+			// everything after -- is positional
+			v.flags.positionals << v.prog_args[i + 1..]
+			break
+		}
+		if !v.flag_token(a) {
+			// positional, unless it was already consumed as a flag's value below
+			v.flags.positionals << a
+			i++
+			continue
+		}
+		// a flag token. Only long flags (--name) consume a separate value token;
+		// short flags (-v) are treated as boolean to avoid swallowing a following
+		// positional (use -n=val or --name val for short aliases needing a value).
+		name, val, has_inline := v.flag_key_val(a)
+		long_flag := a.starts_with('--')
+		if name !in v.flags.vals {
+			if has_inline {
+				v.flags.vals[name] = val
+				i++
+				continue
+			}
+			if long_flag && i + 1 < v.prog_args.len && !v.flag_token(v.prog_args[i + 1]) {
+				v.flags.vals[name] = v.prog_args[i + 1]
+				i += 2
+			} else {
+				v.flags.vals[name] = 'true'
+				i++
+			}
+			continue
+		}
+		// duplicate flag: keep the first value, but still consume its value
+		if long_flag && !has_inline && i + 1 < v.prog_args.len && !v.flag_token(v.prog_args[i + 1]) {
+			i += 2
+		} else {
+			i++
+		}
+	}
+}
+
+// flag_token reports whether a is parsed as a flag rather than a value.
+// flag_lookup returns the value of flag `name`, accepting its single-letter
+// short alias as well. Returns '' when the flag was not passed.
+fn (mut v Vm) flag_lookup(name string) string {
+	if name in v.flags.vals {
+		return v.flags.vals[name]
+	}
+	if name.len > 1 {
+		short := name[..1]
+		if short in v.flags.vals {
+			return v.flags.vals[short]
+		}
+	}
+	return ''
+}
+
+// flag_present_key reports whether flag `name` (or its short alias) was passed
+// at all, regardless of its value.
+fn (mut v Vm) flag_present_key(name string) bool {
+	if name in v.flags.vals {
+		return true
+	}
+	if name.len > 1 {
+		return name[..1] in v.flags.vals
+	}
+	return false
+}
+
+fn (mut v Vm) flag_token(a string) bool {
+	if a == '-' {
+		return false
+	}
+	if !a.starts_with('-') {
+		return false
+	}
+	// a negative number (-5, -3.14) is a value, not a flag
+	if a.len > 1 && a[1] >= `0` && a[1] <= `9` {
+		return false
+	}
+	return true
+}
+
+// flag_key_val splits a flag token into its canonical (dash-stripped) name and
+// any inline value. Returns (name, value, has_inline_value).
+fn (mut v Vm) flag_key_val(a string) (string, string, bool) {
+	raw := a.trim_left('-') // strip leading dashes
+	mut eq := -1
+	for i in 0..raw.len {
+		if raw[i] == `=` {
+			eq = i
+			break
+		}
+	}
+	if eq >= 0 {
+		return raw[..eq], raw[eq + 1..], true
+	}
+	return raw, '', false
+}
+
 // type_name returns the type label of a tagged value.
 fn (mut v Vm) type_name(x i64) string {
 	if v.is_str(x) {
diff --git a/vm/opcodes.v b/vm/opcodes.v
index 208737c..565ab76 100644
--- a/vm/opcodes.v
+++ b/vm/opcodes.v
@@ -181,3 +181,12 @@ const native_sb_len = 192
 // concurrency: spawn/join threads
 const native_spawn = 193
 const native_spawn_join = 194
+
+// interactive input: read a line from stdin
+const native_read_line = 195
+const native_input = 196
+
+// getopt-style flag parsing over args()
+const native_flag_val = 197
+const native_flag_has = 198
+const native_flag_positional = 199
diff --git a/vm/ops.v b/vm/ops.v
index 082b1c2..ba6e601 100644
--- a/vm/ops.v
+++ b/vm/ops.v
@@ -4,6 +4,18 @@ module vm
 import math
 
 fn (mut v Vm) add(a i64, b i64) !i64 {
+	// String + any: coerce the other operand to its string form so that
+	// `"caught: " + e`, `"n=" + count`, and record/array debugging "just
+	// work" the way users expect when building messages.
+	if v.is_str(a) && !v.is_str(b) {
+		return v.alloc_str(v.strings[v.hand(a)] + v.val_str(b, 0))
+	}
+	if v.is_str(b) && !v.is_str(a) {
+		return v.alloc_str(v.val_str(a, 0) + v.strings[v.hand(b)])
+	}
+	if v.is_str(a) && v.is_str(b) {
+		return v.alloc_str(v.strings[v.hand(a)] + v.strings[v.hand(b)])
+	}
 	if v.is_none(a) || v.is_none(b) {
 		return error('cannot use none with +')
 	}
@@ -13,15 +25,6 @@ fn (mut v Vm) add(a i64, b i64) !i64 {
 	if v.is_struct(a) || v.is_struct(b) {
 		return error('cannot add structs with +')
 	}
-	if v.is_str(a) && v.is_str(b) {
-		return v.alloc_str(v.strings[v.hand(a)] + v.strings[v.hand(b)])
-	}
-	if v.is_str(a) {
-		return v.alloc_str(v.strings[v.hand(a)] + v.num_str(b))
-	}
-	if v.is_str(b) {
-		return v.alloc_str(v.num_str(a) + v.strings[v.hand(b)])
-	}
 	if v.is_float(a) || v.is_float(b) {
 		return v.push_float(v.to_f64(a) + v.to_f64(b))
 	}
diff --git a/vm/types.v b/vm/types.v
index 5e5b843..207869d 100644
--- a/vm/types.v
+++ b/vm/types.v
@@ -99,6 +99,20 @@ mut:
 	fn_of_ip   []int          // code offset -> function index (for profiling)
 	max_ops    i64            // instruction budget; 0 = unlimited (fuzzing safety)
 	ops        i64            // instructions executed so far
+	flags      FlagArgs       // cached getopt parse of prog_args (lazy)
+}
+
+// FlagArgs is the parsed view of the command-line arguments, computed lazily
+// and shared by flag_val / flag_has / flag_positional so that a value consumed
+// as a flag value is never also returned as a positional.
+struct FlagArgs {
+	// parsed indicates the parse is only valid when built against the same
+	// argv length as prog_args currently has (args never change at runtime).
+mut:
+	parsed  bool
+	vals    map[string]string // canonical flag name -> value ('true' for boolean w/o inline)
+	ordered []string          // flag names in first-appearance order
+	positionals []string      // non-flag arguments not consumed as flag values
 }
 
 fn bool_i64(b bool) i64 {