Add nominal tagged unions

apps/docs/content/language/alpha-status.md

@@ -14,7 +14,8 @@ The implemented language includes:
 
 - modules, imports, visibility, globals, and typed constants;
 - integers, floating-point values, booleans, characters, and string and byte data;
-- structs, scalar enums, fixed arrays, runtime slices, structural unions, and exhaustive matching;
+- structs, scalar enums, nominal unions, fixed arrays, runtime slices, structural unions, and
+  exhaustive matching;
 - functions, first-class callables, pipelines, generics, interfaces, and specialization;
 - mutable places, affine ownership, shared and exclusive borrowing, explicit moves, and
   deterministic `Drop` on structured exits;

apps/docs/content/language/diagnostics.md

@@ -16,11 +16,11 @@ $ pnpm --filter @silklang/compiler documentation:generate
 | `LEX` | Lexical | 7 |
 | `PAR` | Parser | 4 |
 | `MOD` | Module | 3 |
-| `SEM` | Semantic | 155 |
+| `SEM` | Semantic | 161 |
 | `OWN` | Ownership | 16 |
 | `LAY` | Layout | 1 |
 
-There are 186 codes in total.
+There are 192 codes in total.
 
 ## Lexical (`LEX`)
 
@@ -73,7 +73,7 @@ There are 186 codes in total.
 | `SEM0017` |  | `Duplicate field name <spelling>` |
 | `SEM0018` |  | `Expected a type, found <spelling>` |
 | `SEM0019` |  | `Public declaration exposes private type <type>` |
-| `SEM0020` |  | `Inline recursive struct layout: <join>` |
+| `SEM0020` |  | `Inline recursive aggregate layout: <join>` |
 | `SEM0021` |  | `Cannot construct <type> because its raw constructor is not available at this site` |
 | `SEM0022` |  | `<type> has no field <field>` |
 | `SEM0023` |  | `Field <field> is initialized more than once` |
@@ -210,6 +210,12 @@ There are 186 codes in total.
 | `SEM0161` | Stable code for a scalar enum pattern naming a member of another enum. | `Enum pattern from <actual> cannot match <expected>` |
 | `SEM0162` | Stable code for an integer literal pattern used against a scalar enum. | `Integer pattern <value> cannot match enum <enum>` |
 | `SEM0163` | Stable code for effect-block return sites whose success types disagree. | `Effect block return sites have incompatible types: <join>` |
+| `SEM0164` | Stable code for a nominal union declaration with no variants. | `Union <unionName> must declare at least one variant` |
+| `SEM0165` | Stable code for a repeated variant name within one nominal union. | `Duplicate union variant <spelling>` |
+| `SEM0166` | Stable code for a named-field variant whose braces contain no field. | `Union variant <variantName> must omit braces or declare at least one field` |
+| `SEM0167` | Stable code for a variant selector absent from its resolved nominal union. | `Union <unionName> has no variant <variantName>` |
+| `SEM0168` | Stable code for a variant qualifier that does not name a nominal union. | `Expected a nominal union, found <actual>` |
+| `SEM0169` | Stable code for construction through an incomplete nominal union declaration. | `Cannot construct invalid nominal union <unionName>` |
 
 ## Ownership (`OWN`)
 

apps/docs/content/language/stdlib/char.md

@@ -55,7 +55,7 @@ Public declarations: 8.
 ## `fromU32`
 
 ```silk
-pub fn fromU32(value: u32) -> Option<char>
+pub fn fromU32(value: u32) -> silk/option.Option<char>
 ```
 
 Converts an integer to a Unicode scalar. Returns `None` for `0xD800` through `0xDFFF` and values

apps/docs/content/language/stdlib/child-process.md

@@ -67,8 +67,8 @@ effect fn program() -> i32
     |> Effect.provideMut<Process.ChildProcess>(&mut provider)
     |> Effect.provideMut<Allocator>(&mut allocator)
   return match move Process.exitCode(&outcome) {
-    Option.Some<i32> {value} => 35 + value
-    Option.None {} => 1
+    Option.Option<i32>.Some {value} => 35 + value
+    Option.Option<i32>.None => 1
   }
 }
 
@@ -297,7 +297,7 @@ Creates a process failure with a provider-defined numeric code for diagnostics.
 ## `providerCode`
 
 ```silk
-pub fn providerCode(error: &silk/child_process.ProcessError) -> Option<i32>
+pub fn providerCode(error: &silk/child_process.ProcessError) -> silk/option.Option<i32>
 ```
 
 Returns the provider-defined numeric code, or `None` when the failure has no such code.
@@ -629,7 +629,7 @@ Reports whether a signal terminated the child instead of an exit code.
 ## `exitCode`
 
 ```silk
-pub fn exitCode(outcome: &silk/child_process.ProcessOutcome) -> Option<i32>
+pub fn exitCode(outcome: &silk/child_process.ProcessOutcome) -> silk/option.Option<i32>
 ```
 
 Returns the exit code, or `None` when a signal terminated the child.
@@ -639,7 +639,7 @@ Returns the exit code, or `None` when a signal terminated the child.
 ## `terminatingSignal`
 
 ```silk
-pub fn terminatingSignal(outcome: &silk/child_process.ProcessOutcome) -> Option<i32>
+pub fn terminatingSignal(outcome: &silk/child_process.ProcessOutcome) -> silk/option.Option<i32>
 ```
 
 Returns the terminating signal number, or `None` when the child returned an exit code.

apps/docs/content/language/stdlib/effect.md

@@ -28,7 +28,7 @@ owned provider bindings have distinct borrowing and capture behavior.
 
 ## Gotchas
 
-Typed failures are outcomes that combinators can reify and recover. Traps are not: they bypass
+Typed failures are outcomes that combinators can materialize and recover. Traps are not: they bypass
 [`catchAll`](#declaration-73696c6b2f6566666563743a3a6361746368416c6c), [`ensuring`](#declaration-73696c6b2f6566666563743a3a656e737572696e67), and Drop hooks. [`suspend`](#declaration-73696c6b2f6566666563743a3a73757370656e64) crosses the stack-safe execution boundary
 while preserving all three channels exactly; frame exhaustion is fatal.
 
@@ -240,8 +240,8 @@ Executes `protected` once and converts its success or typed failure into ordinar
 
 ### Details
 
-The returned Effect still requires `R`, because reification does not provide services. Its typed
-failure row is empty: an `E` becomes [`Failure`](./result.md#declaration-73696c6b2f726573756c743a3a4661696c757265) data instead of propagating. Traps are not typed
+The returned Effect still requires `R`, because conversion does not provide services. Its typed
+failure row is empty: an `E` becomes [`Failure`](./result.md#declaration-73696c6b2f726573756c743a3a526573756c743a3a76617269616e743a31) data instead of propagating. Traps are not typed
 failures and therefore are not captured.
 
 ### Examples
@@ -265,10 +265,8 @@ effect fn load() -> i32
 pub fn main() -> i32 {
   let completed = run Effect.result(load())
   return match move completed {
-    Result.Result<i32, Problem> {value: outcome} => match move outcome {
-      Result.Success<i32> {value} => value
-      Result.Failure<Problem> {error} => error.answer
-    }
+    Result.Result<i32, Problem>.Success {value} => value
+    Result.Result<i32, Problem>.Failure {error} => error.answer
   }
 }
 ```
@@ -518,7 +516,7 @@ Runs a finalizer after the Effect completes, whatever its outcome, and preserves
 
 ### Details
 
-The protected Effect is reified into Result data before the finalizer runs, which is what fixes
+The protected Effect is converted into Result data before the finalizer runs, which is what fixes
 the order: a typed failure reaches this body as data rather than as a propagation, so the
 protected Effect's own frame — and every local it cleans up — is already gone by the time the
 finalizer starts. The finalizer therefore exits last, in reverse acquisition order against the

apps/docs/content/language/stdlib/filesystem.md

@@ -534,7 +534,7 @@ the fields callers should use for recovery.
 ## `providerCode`
 
 ```silk
-pub fn providerCode(error: &silk/filesystem.FileError) -> Option<i32>
+pub fn providerCode(error: &silk/filesystem.FileError) -> silk/option.Option<i32>
 ```
 
 Borrows an error and returns its provider-specific numeric detail, if one was retained.
@@ -688,10 +688,10 @@ fails with the `InvalidPath` reason. Resolution is lexical and never accesses th
 ## `parent`
 
 ```silk
-pub effect fn parent(self: &silk/filesystem.Path) -> Option<silk/filesystem.Path> ! OutOfMemoryError ? &mut Allocator
+pub effect fn parent(self: &silk/filesystem.Path) -> silk/option.Option<silk/filesystem.Path> ! OutOfMemoryError ? &mut Allocator
 ```
 
-Allocates an independently owned parent path, or [`None`](./option.md#declaration-73696c6b2f6f7074696f6e3a3a4e6f6e65) when `self` is root.
+Allocates an independently owned parent path, or [`None`](./option.md#declaration-73696c6b2f6f7074696f6e3a3a4f7074696f6e3a3a76617269616e743a30) when `self` is root.
 
 ### Details
 

apps/docs/content/language/stdlib/hash-map.md

@@ -186,7 +186,7 @@ impl Drop for silk/hash_map.HashMap<K, V>
 ## `insert`
 
 ```silk
-pub effect fn insert<K, V>(self: &mut silk/hash_map.HashMap<K, V>, key: K, value: V) -> Option<V> ! OutOfMemoryError ? &mut Allocator
+pub effect fn insert<K, V>(self: &mut silk/hash_map.HashMap<K, V>, key: K, value: V) -> silk/option.Option<V> ! OutOfMemoryError ? &mut Allocator
 ```
 
 Inserts one owned key and value, answering with the value an equivalent key already held.
@@ -218,7 +218,7 @@ This function consumes the probe key. It does not change the map or move a store
 ## `indexOf`
 
 ```silk
-pub fn indexOf<K, V>(self: &silk/hash_map.HashMap<K, V>, key: K) -> Option<usize>
+pub fn indexOf<K, V>(self: &silk/hash_map.HashMap<K, V>, key: K) -> silk/option.Option<usize>
 ```
 
 Returns the bucket holding an entry under a key equivalent to one probe key, or an absent value.
@@ -234,7 +234,7 @@ This function consumes the probe key.
 ## `get`
 
 ```silk
-pub fn get<K, V>(self: &silk/hash_map.HashMap<K, V>, key: K) -> Option<V>
+pub fn get<K, V>(self: &silk/hash_map.HashMap<K, V>, key: K) -> silk/option.Option<V>
 ```
 
 Returns the value held under a key equivalent to one probe key, or an absent value.
@@ -270,7 +270,7 @@ count unchanged.
 ## `remove`
 
 ```silk
-pub fn remove<K, V>(self: &mut silk/hash_map.HashMap<K, V>, key: K) -> Option<V>
+pub fn remove<K, V>(self: &mut silk/hash_map.HashMap<K, V>, key: K) -> silk/option.Option<V>
 ```
 
 Removes the entry under a key equivalent to one probe key and answers with its value.

apps/docs/content/language/stdlib/hash-set.md

@@ -214,7 +214,7 @@ This function consumes the probe element. It does not change the set or move a s
 ## `indexOf`
 
 ```silk
-pub fn indexOf<T>(self: &silk/hash_set.HashSet<T>, value: T) -> Option<usize>
+pub fn indexOf<T>(self: &silk/hash_set.HashSet<T>, value: T) -> silk/option.Option<usize>
 ```
 
 Returns the bucket holding an element equivalent to one probe element, or an absent value.
@@ -229,7 +229,7 @@ This function consumes the probe element.
 ## `remove`
 
 ```silk
-pub fn remove<T>(self: &mut silk/hash_set.HashSet<T>, value: T) -> Option<T>
+pub fn remove<T>(self: &mut silk/hash_set.HashSet<T>, value: T) -> silk/option.Option<T>
 ```
 
 Removes the element equivalent to one probe element and answers with it.

apps/docs/content/language/stdlib/host-input.md

@@ -13,7 +13,7 @@ lossless pass-through.
 ## Details
 
 Arguments include the program name at index zero and retain host order. A missing argument index
-or unset variable is [`None`](./option.md#declaration-73696c6b2f6f7074696f6e3a3a4e6f6e65), while [`HostInputError`](#declaration-73696c6b2f686f73745f696e7075743a3a486f7374496e7075744572726f72) means the provider could not answer.
+or unset variable is [`None`](./option.md#declaration-73696c6b2f6f7074696f6e3a3a4f7074696f6e3a3a76617269616e743a30), while [`HostInputError`](#declaration-73696c6b2f686f73745f696e7075743a3a486f7374496e7075744572726f72) means the provider could not answer.
 Returned [`Bytes`](./bytes.md#declaration-73696c6b2f62797465733a3a4279746573) values are independently owned, so lookup operations also carry explicit
 [`OutOfMemoryError`](./allocator.md#declaration-73696c6b2f616c6c6f6361746f723a3a4f75744f664d656d6f72794572726f72) and [`Allocator`](./allocator.md#declaration-73696c6b2f616c6c6f6361746f723a3a416c6c6f6361746f72) channels.
 
@@ -152,7 +152,7 @@ A provider that cannot inspect the process arguments fails with `HostInputError`
 ### Operation `argument`
 
 ```silk
-effect fn argument(index: usize) -> Option<silk/bytes.Bytes> ! HostInputError | OutOfMemoryError ? &mut HostInput | &mut Allocator
+effect fn argument(index: usize) -> silk/option.Option<silk/bytes.Bytes> ! HostInputError | OutOfMemoryError ? &mut HostInput | &mut Allocator
 ```
 
 Copies one argument as raw bytes, or returns `None` when `index` is out of range.
@@ -167,7 +167,7 @@ produces `HostInputError`; ownership allocation produces `OutOfMemoryError`.
 ### Operation `variable`
 
 ```silk
-effect fn variable(name: &[u8]) -> Option<silk/bytes.Bytes> ! HostInputError | OutOfMemoryError ? &mut HostInput | &mut Allocator
+effect fn variable(name: &[u8]) -> silk/option.Option<silk/bytes.Bytes> ! HostInputError | OutOfMemoryError ? &mut HostInput | &mut Allocator
 ```
 
 Copies one environment value as raw bytes, or returns `None` when `name` is unset.
@@ -212,7 +212,7 @@ The count includes the program name at index zero. Provider failure produces
 ## `argument`
 
 ```silk
-pub effect fn argument(index: usize) -> Option<silk/bytes.Bytes> ! HostInputError | OutOfMemoryError ? &mut HostInput | &mut Allocator
+pub effect fn argument(index: usize) -> silk/option.Option<silk/bytes.Bytes> ! HostInputError | OutOfMemoryError ? &mut HostInput | &mut Allocator
 ```
 
 Copies one process argument through the active [`HostInput`](#declaration-73696c6b2f686f73745f696e7075743a3a486f7374496e707574) provider.
@@ -227,7 +227,7 @@ independently owned and can contain bytes that are not valid UTF-8.
 ## `variable`
 
 ```silk
-pub effect fn variable(name: &[u8]) -> Option<silk/bytes.Bytes> ! HostInputError | OutOfMemoryError ? &mut HostInput | &mut Allocator
+pub effect fn variable(name: &[u8]) -> silk/option.Option<silk/bytes.Bytes> ! HostInputError | OutOfMemoryError ? &mut HostInput | &mut Allocator
 ```
 
 Copies one environment value selected by a raw byte name.
@@ -242,7 +242,7 @@ process environment. The returned [`Bytes`](./bytes.md#declaration-73696c6b2f627
 ## `variableNamed`
 
 ```silk
-pub effect fn variableNamed(name: string) -> Option<silk/bytes.Bytes> ! HostInputError | OutOfMemoryError ? &mut HostInput | &mut Allocator
+pub effect fn variableNamed(name: string) -> silk/option.Option<silk/bytes.Bytes> ! HostInputError | OutOfMemoryError ? &mut HostInput | &mut Allocator
 ```
 
 Copies one environment value selected by a valid UTF-8 name.

apps/docs/content/language/stdlib/i16.md

@@ -118,7 +118,7 @@ this function when an out-of-range value is a program error.
 ## `checkedToU8`
 
 ```silk
-pub fn checkedToU8(value: i16) -> Option<u8>
+pub fn checkedToU8(value: i16) -> silk/option.Option<u8>
 ```
 
 Converts `value` to `u8`, or returns `None` if `value` is outside the `u8`
@@ -140,7 +140,7 @@ this function when an out-of-range value is a program error.
 ## `checkedToU16`
 
 ```silk
-pub fn checkedToU16(value: i16) -> Option<u16>
+pub fn checkedToU16(value: i16) -> silk/option.Option<u16>
 ```
 
 Converts `value` to `u16`, or returns `None` if `value` is outside the `u16`
@@ -162,7 +162,7 @@ this function when an out-of-range value is a program error.
 ## `checkedToU32`
 
 ```silk
-pub fn checkedToU32(value: i16) -> Option<u32>
+pub fn checkedToU32(value: i16) -> silk/option.Option<u32>
 ```
 
 Converts `value` to `u32`, or returns `None` if `value` is outside the `u32`
@@ -184,7 +184,7 @@ this function when an out-of-range value is a program error.
 ## `checkedToU64`
 
 ```silk
-pub fn checkedToU64(value: i16) -> Option<u64>
+pub fn checkedToU64(value: i16) -> silk/option.Option<u64>
 ```
 
 Converts `value` to `u64`, or returns `None` if `value` is outside the `u64`
@@ -206,7 +206,7 @@ this function when an out-of-range value is a program error.
 ## `checkedToUsize`
 
 ```silk
-pub fn checkedToUsize(value: i16) -> Option<usize>
+pub fn checkedToUsize(value: i16) -> silk/option.Option<usize>
 ```
 
 Converts `value` to `usize`, or returns `None` if `value` is outside the `usize`
@@ -228,7 +228,7 @@ this function when an out-of-range value is a program error.
 ## `checkedToI8`
 
 ```silk
-pub fn checkedToI8(value: i16) -> Option<i8>
+pub fn checkedToI8(value: i16) -> silk/option.Option<i8>
 ```
 
 Converts `value` to `i8`, or returns `None` if `value` is outside the `i8`
@@ -250,7 +250,7 @@ can select `i16` as both source and destination.
 ## `checkedToI16`
 
 ```silk
-pub fn checkedToI16(value: i16) -> Option<i16>
+pub fn checkedToI16(value: i16) -> silk/option.Option<i16>
 ```
 
 Returns `Some` with `value` unchanged as `i16`. Use this function when generic
@@ -271,7 +271,7 @@ Converts `value` exactly to `i32`. Every `i16` value is representable.
 ## `checkedToI32`
 
 ```silk
-pub fn checkedToI32(value: i16) -> Option<i32>
+pub fn checkedToI32(value: i16) -> silk/option.Option<i32>
 ```
 
 Converts `value` exactly to `i32` and returns `Some`. Every `i16` value is
@@ -292,7 +292,7 @@ Converts `value` exactly to `i64`. Every `i16` value is representable.
 ## `checkedToI64`
 
 ```silk
-pub fn checkedToI64(value: i16) -> Option<i64>
+pub fn checkedToI64(value: i16) -> silk/option.Option<i64>
 ```
 
 Converts `value` exactly to `i64` and returns `Some`. Every `i16` value is
@@ -313,7 +313,7 @@ Converts `value` exactly to `isize`. Every `i16` value is representable.
 ## `checkedToIsize`
 
 ```silk
-pub fn checkedToIsize(value: i16) -> Option<isize>
+pub fn checkedToIsize(value: i16) -> silk/option.Option<isize>
 ```
 
 Converts `value` exactly to `isize` and returns `Some`. Every `i16` value is
@@ -547,7 +547,7 @@ boundary value is the required overflow result.
 ## `checkedAdd`
 
 ```silk
-pub fn checkedAdd(left: i16, right: i16) -> Option<i16>
+pub fn checkedAdd(left: i16, right: i16) -> silk/option.Option<i16>
 ```
 
 Returns `Some` with `left + right`, or `None` if the result is outside the `i16` range.
@@ -558,7 +558,7 @@ Use this function when overflow is input data.
 ## `checkedSubtract`
 
 ```silk
-pub fn checkedSubtract(left: i16, right: i16) -> Option<i16>
+pub fn checkedSubtract(left: i16, right: i16) -> silk/option.Option<i16>
 ```
 
 Returns `Some` with `left - right`, or `None` if the result is outside the `i16` range.
@@ -569,7 +569,7 @@ Use this function when overflow is input data.
 ## `checkedMultiply`
 
 ```silk
-pub fn checkedMultiply(left: i16, right: i16) -> Option<i16>
+pub fn checkedMultiply(left: i16, right: i16) -> silk/option.Option<i16>
 ```
 
 Returns `Some` with `left * right`, or `None` if the result is outside the `i16` range.
@@ -580,7 +580,7 @@ Use this function when overflow is input data.
 ## `checkedDivide`
 
 ```silk
-pub fn checkedDivide(left: i16, right: i16) -> Option<i16>
+pub fn checkedDivide(left: i16, right: i16) -> silk/option.Option<i16>
 ```
 
 Returns `Some` with `left / right`, or `None` if `right` is zero or [`MIN`](#declaration-73696c6b2f6931363a3a4d494e) is
@@ -591,7 +591,7 @@ divided by `-1`. Use this function when an invalid quotient is input data.
 ## `checkedRemainder`
 
 ```silk
-pub fn checkedRemainder(left: i16, right: i16) -> Option<i16>
+pub fn checkedRemainder(left: i16, right: i16) -> silk/option.Option<i16>
 ```
 
 Returns `Some` with the remainder, or `None` if `right` is zero or [`MIN`](#declaration-73696c6b2f6931363a3a4d494e) is