Combine throw and create #43
Conversation
proposals/Level-1.md
Outdated
| [exception index space](#exception-index-space). This index is referred to as | ||
| the `exception tag`. The `tagged exception type` is the corresponding | ||
| [exception index space](#exception-index-space). This static index refers to the | ||
| corresponding runtime index that uniquely identifies the exception type, and is |
There was a problem hiding this comment.
Suggestion: Maybe it's even clearer if you avoid calling the runtime thing an "index" in the first place. How about changing wording to use "tag" right away?
There was a problem hiding this comment.
Sound good. Changing.
proposals/Level-1.md
Outdated
| the `exception tag`. The `tagged exception type` is the corresponding | ||
| [exception index space](#exception-index-space). This static index refers to the | ||
| corresponding runtime index that uniquely identifies the exception type, and is | ||
| called the `exception tag`. The `tagged exception type` is the corresponding |
There was a problem hiding this comment.
Terminology nitpick: Technically what's defined in the exception section is not a type. What an exception definition defines is a fresh tag, which is a runtime value that has the ascribed exception type (and multiple tags can have the same type yet be different tags). This may be nitpicking, but the difference is that it clarifies that (1) multiple tags can have the same type, and (2) dispatch is on values not types (types have no runtime representation in Wasm).
There was a problem hiding this comment.
Ok. reworking this text.
proposals/Level-1.md
Outdated
| 1. The `except` instruction which creates a WebAssembly instance of the | ||
| corresponding tagged exception type, and pushes a reference to it onto the | ||
| stack. | ||
| 1. The `throw` instruction which creates a WebAssembly instance of the |
There was a problem hiding this comment.
Suggestion: I would say it creates an exception value with the corresponding tag.
There was a problem hiding this comment.
Ok. Reworking the code to match.
proposals/Level-1.md
Outdated
| @@ -114,8 +113,7 @@ Exception tags are used by: | |||
| ### The exception reference data type | |||
|
|
|||
| Data types are extended to have a new `except_ref` type. The representation of | |||
| an exception type is left to the host VM, but its size must be fixed. The actual | |||
| number of bytes it takes to represent any `except_ref` is left to the host VM. | |||
| an exception type is left to the host VM. | |||
There was a problem hiding this comment.
"exception type" -> "exception value"
proposals/Level-1.md
Outdated
| The `throw` throws the exception on top of the stack. The exception is popped | ||
| off the top of the stack before throwing. | ||
| The `throw` instruction takes an exception index as an immediate argument. That | ||
| index is used to identify the tagged exception type to throw. The values to |
There was a problem hiding this comment.
Suggestion: "tagged exception type" -> "exception tag"
"values to throw" -> "argument values"
There was a problem hiding this comment.
Rewritten to match changes.
proposals/Level-1.md
Outdated
| The `throw` instruction takes an exception index as an immediate argument. That | ||
| index is used to identify the tagged exception type to throw. The values to | ||
| throw (corresponding to the signature) are popped from the top of the stack, and | ||
| an exception is created. This includes attaching a stack track to the exception. |
There was a problem hiding this comment.
Nit: The stack trace isn't part of the core semantics and its presence may depend on the embedder.
proposals/Level-1.md
Outdated
| @@ -177,23 +188,24 @@ If the selected catch block does not throw an exception, it must yield the | |||
| value(s) expected by the corresponding catching try block. This includes popping | |||
| the caught exception. | |||
|
|
|||
| Note that a caught exception can be rethrown using the `throw` instruction. | |||
| Note that a caught exception value can be rethrown using the `throw` | |||
proposals/Level-1.md
Outdated
|
|
||
| | Field | Type | Description | | ||
| |-------|------|-------------| | ||
| | `count` | `varuint32` | The number of types in the signature | | ||
| | `type` | `value_type*` | The type of each element in the signature | | ||
|
|
||
| Note: An `except_type` is not actually a type, just an exception definition that |
There was a problem hiding this comment.
Well, the exception type in an exn def is indeed the type of the defined tag, so I believe this note isn't necessary (and probably misleading).
Combine the throw and exception create instructions into a single 'throw' instruction. Add back from the original proposal the 'rethrow' instruction that can rethrow a caught exception.
Also cleans up cases some confusion of exception tags and exception indices. That is, the index is the static value used in the module, while the tag is the corresponding exception identifier for that index.