A simple stack in WA

simple_stack.wat

(module
  (func $needs_more_space (result i32)
    block (result i32) ;; available space
      get_global 1
      i32.const 128 ;; 128 bytes = 1024 bits
      i32.const 64
      i32.mul
      i32.mul
    end
    block (result i32) ;; next index
      get_global 0
      i32.const 4 ;; wordsize is 4 bytes
      i32.add
    end
    i32.lt_u
  )
  (func $is_empty (result i32)
    get_global 0
    i32.const 0
    i32.eq
  )
  (func $head (result i32)
    get_global 0
    i32.const 4
    i32.sub
  )
  (func $inc_ind
    get_global 0
    i32.const 4
    i32.add
    set_global 0
  )
  (func $dec_ind
    get_global 0
    i32.const 4
    i32.sub
    set_global 0
  )
  (func $push (param $v i32)
    call $needs_more_space
    if
      i32.const 1
      grow_memory
      i32.const 1
      i32.add
      set_global 1
    else
    end
    block
      get_global 0
      get_local $v
      i32.store
    end
    call $inc_ind
  )
  (func $pop (result i32)
    call $is_empty
    if (result i32)
      i32.const -1
    else
      call $head
      i32.load
      call $dec_ind
    end
  )
  (global (mut i32) (i32.const 0)) ;; index
  (global (mut i32) (i32.const 0)) ;; size
  (memory 0)
  (export "push" (func $push))
  (export "pop" (func $pop))
)