Miscellaneous

end

Terminates a block, loop, or if construct in the linear (non-folded) text format. In the folded S-expression format, closing parentheses serve this purpose instead.

Example:

;; Linear format uses end to close blocks
block $my_block
  i32.const 42
  br $my_block
end

;; Linear if/else also uses end
i32.const 1
if (result i32)
  i32.const 10
else
  i32.const 20
end

---

offset

Specifies a byte offset for memory load/store instructions, or the initialization offset for active data and element segments. Defaults to 0 if omitted.

Example:

;; Memory load with offset
(i32.load offset=8 (i32.const 0))    ;; loads from address 0+8

;; Memory store with offset
(i32.store offset=4 (i32.const 0) (i32.const 42))

;; Active data segment with explicit offset
(data (offset (i32.const 100)) "hello")

;; Active element segment with offset
(elem (table $t) (offset (i32.const 0)) func $f)

---

align

Specifies the expected alignment hint for memory load/store instructions as a power of 2 in bytes. This is a performance hint to the engine — unaligned accesses are still valid but may be slower. The alignment must not exceed the natural alignment of the operation.

Example:

;; Natural alignment (4 bytes for i32)
(i32.load align=4 (i32.const 0))

;; Unaligned access (1-byte alignment)
(i32.load align=1 (i32.const 3))

;; Combined with offset
(f64.load offset=16 align=8 (i32.const 0))

---

declare

Element segment mode that declares function references without initializing them into a table. Required for functions used only with ref.func that aren’t placed in any table.

Example:

;; Declare functions for use with ref.func
(elem declare func $callback $handler)

;; Now ref.func can reference these functions
(func $get_callback (result funcref)
  (ref.func $callback))

---

any

Abstract heap type representing any reference value (GC proposal). Used in ref type annotations. The abbreviated form anyref is equivalent to (ref null any).

Example:

;; Non-nullable reference to any value
(param $val (ref any))

;; Nullable reference (same as anyref)
(local $obj (ref null any))

;; Null reference of type any
(ref.null any)

---

eq

Abstract heap type for values that support structural equality (GC proposal). Subtype of any. Used in ref type annotations. The abbreviated form eqref is equivalent to (ref null eq).

Example:

;; Non-nullable eq reference
(param $val (ref eq))

;; Nullable (same as eqref)
(local $item (ref null eq))

;; Compare two eq references
(ref.eq (local.get $a) (local.get $b))

---

extern

Abstract heap type for external (host) references (GC proposal). Used in ref type annotations. The abbreviated form externref is equivalent to (ref null extern).

Example:

;; Non-nullable external reference
(param $obj (ref extern))

;; Nullable (same as externref)
(local $host_val (ref null extern))

;; Convert between any and extern
(extern.convert_any (local.get $val))
(any.convert_extern (local.get $ext))

---

i31

Heap type for 31-bit integers packed into a reference (GC proposal). Subtype of eq. Used in ref type annotations. The abbreviated form i31ref is equivalent to (ref null i31).

Example:

;; Non-nullable i31 reference
(param $num (ref i31))

;; Nullable (same as i31ref)
(local $boxed (ref null i31))

;; Pack and unpack i31 values
(ref.i31 (i32.const 42))
(i31.get_s (local.get $boxed))

---

none

Bottom heap type for the any hierarchy (GC proposal). The only value of type (ref null none) is null. The abbreviated form nullref is equivalent to (ref null none).

Example:

;; The null reference type
(global $empty (ref null none) (ref.null none))

;; Subtype of all reference types in the any hierarchy
;; none <: i31, struct, array, eq, any

---

nofunc

Bottom heap type for the func hierarchy (GC proposal). The only value of type (ref null nofunc) is null. The abbreviated form nullfuncref is equivalent to (ref null nofunc).

Example:

;; The null function reference type
(global $no_fn (ref null nofunc) (ref.null nofunc))

;; Subtype of all function reference types
;; nofunc <: func

---

noexn

Bottom heap type for the exn hierarchy (exception handling proposal). The only value of type (ref null noexn) is null. The abbreviated form nullexnref is equivalent to (ref null noexn).

Example:

;; The null exception reference type
(global $no_exn (ref null noexn) (ref.null noexn))

;; Subtype of all exception reference types
;; noexn <: exn

---

noextern

Bottom heap type for the extern hierarchy (GC proposal). The only value of type (ref null noextern) is null. The abbreviated form nullexternref is equivalent to (ref null noextern).

Example:

;; The null external reference type
(global $no_ext (ref null noextern) (ref.null noextern))

;; Subtype of all external reference types
;; noextern <: extern

---

try

Define a block with exception handling (legacy syntax, replaced by try_table in the current spec). Contains a do block for the main body and catch/catch_all clauses for exception handlers.

Example:

(try
  (do (call $may_throw))
  (catch $error (drop)))

---

do

Mark the main body inside a try block (legacy exception handling syntax). The do clause contains the instructions that may throw exceptions.

Example:

(try
  (do (nop))
  (catch_all (nop)))

---