Skip to content

try_table

try_table creates a block that can catch exceptions thrown during its execution. Catch clauses specify which exception tags to handle and where to branch when caught.

(module
  (tag $e-i32 (param i32))

  (func $example (result i32)
    (block $handler (result i32)
      (try_table (result i32) (catch $e-i32 $handler)
        (throw $e-i32 (i32.const 42))
        (i32.const 0)
      )
    )
  )
)

Catch clause variants

Clause	Syntax	Behavior
`catch`	`(catch $tag $label)`	Catches the tag, branches to label with the tag’s payload values
`catch_ref`	`(catch_ref $tag $label)`	Like `catch`, also pushes an `exnref`
`catch_all`	`(catch_all $label)`	Catches any exception, branches to label
`catch_all_ref`	`(catch_all_ref $label)`	Like `catch_all`, also pushes an `exnref`

Tags

Tags declare exception types with their payload signatures:

(tag $my-error (param i32 i32))

When a catch clause matches, the tag’s parameter types are delivered to the branch target label.

Stack typing

try_table blocks follow the same typing rules as block — they declare params and results.
The LSP validates that the body leaves the correct result types on the stack.
Catch clauses are declarative (label references) and don’t contain code.

throw $tag — throws an exception with the given tag
throw_ref — rethrows a caught exception reference
block / loop / if — other structured control flow