Breaking down the wast format

fn_calls.rs

#[no_mangle]
pub extern "C" fn double_subtract5_add1(x: i32) -> i32 {
    let result = double(x) + negate(5) + 1;
    return result;
}

#[no_mangle]
pub fn double(x: i32) -> i32 {
    return x * 2;
}

#[no_mangle]
pub fn negate(x: i32) -> i32 {
    return -1 * x;
}

fn_calls.wast

;; https://github.com/sunfishcode/wasm-reference-manual/blob/master/WebAssembly.md#known-sections

(module
 ;; Types section 
 (type $0 (func (param i32) (result i32)))
 (type $1 (func (param i32 i32) (result i32)))
 (type $2 (func (param i32 i32 i32)))
 
 ;; The rest are for Rust stdlib functions (omitted).
 (type $3 (func (param i32 i32 i32 i32) (result i32)))
 ;; ...
 
 ;; Looks like this is used in allocation.
 (global $global$0 (mut i32) (i32.const 1156384))
 
 ;; Table section?
 (table 259 259 anyfunc)
 
 ;; Linear memory section?
 (memory $0 18)
 ;; Omitting some statically-allocated Rust stdlib stuff...
 ;; ...
 (data (i32.const 107756) "\01\00\00\00\00\00\00\00g\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00h\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00i\00\00\00\00\00\00\00\00")
 
 ;; Export section
 (export "memory" (memory $0))
 (export "double_subtract5_add1" (func $double_subtract5_add1))
 (export "double" (func $double))
 (export "negate" (func $negate))
 
 ;; Function section
 
 ;; (x: i32) -> i32
 ;; Computes `double(x) + negate(5) + 1`.
 (func $double_subtract5_add1 (; 0 ;) (type $0) (param $var$0 i32) (result i32)
  (i32.add  ; (+
   (i32.add  ; (+
    (call $double  ; (double x)
     (get_local $var$0)
    )
    (call $negate  ; (negate 5))
     (i32.const 5)
    )
   )
   (i32.const 1)  ; 1)
  )
 )
       
 ;; (x: i32) -> i32
 ;; Returns `x * 2`.
 (func $double (; 1 ;) (type $0) (param $var$0 i32) (result i32)
  (i32.shl  ; shift left once
   (get_local $var$0)
   (i32.const 1)
  )
 )
       
 ;; (x: i32) -> i32
 ;; Computes `x * -1`.
 (func $negate (; 2 ;) (type $0) (param $var$0 i32) (result i32)
  (i32.sub
   (i32.const 0)
   (get_local $var$0)
  )
 )
       
 ;; Skipping a rather large # of Rust stdlib functions here...
 ;; All of this variety:
 (func $__rust_alloc (; 3 ;) (type $1) (param $var$0 i32) (param $var$1 i32) (result i32)
  (call $__rdl_alloc
   (get_local $var$0)
   (get_local $var$1)
  )
 )
       
 ;; ...
 
 ;; custom section "linking", size 5
)