如何簡化這個ocaml模式匹配代碼？

Question

我正在寫一個簡單的小型ocaml程序，它從文件中讀取代數語句，使用ocamllex/ocamlyacc將其解析爲AST，將其縮小並打印出來。我減少表情的部分似乎有點......很難看。有什麼辦法可以簡化它嗎？

(* ocaml doesn't seem to be able to take arithmetic operators 
as functions, so define these wrappers for them *) 
let add x y = 
    x + y 

let sub x y = 
    x - y 

let mul x y = 
    x * y 

let div x y = 
    x/y 

(* Are term1 and term2 both ints? *) 
let both_ints term1 term2 = 
    match (term1, term2) with 
    | (Term (Number x), Term (Number y)) -> true 
    | (_, _) -> false 

(* We know that both terms are reducable to numbers, so combine 
    them *) 
let combine_terms func x y = 
    match (x, y) with 
     (Term (Number t1), Term (Number t2)) -> 
     (Term (Number (func t1 t2))) 
    | (_, _) -> raise InvalidArg 

(* Reduce the expression as much as possible *) 
let rec reduce_expr expr = 
    match expr with 
     Plus (x, y) -> 
     let reduced_x = reduce_expr x 
     and reduced_y = reduce_expr y in 
     if both_ints reduced_x reduced_y then 
     (combine_terms add reduced_x reduced_y) 
     else 
     Plus (reduced_x, reduced_y) 
    | Minus (x, y) -> 
     let reduced_x = reduce_expr x 
     and reduced_y = reduce_expr y in 
     if both_ints reduced_x reduced_y then 
     (combine_terms sub reduced_x reduced_y) 
     else 
     Minus (reduced_x, reduced_y) 
    | Multiply (x, y) -> 
     let reduced_x = reduce_expr x 
     and reduced_y = reduce_expr y in 
     if both_ints reduced_x reduced_y then 
     (combine_terms mul reduced_x reduced_y) 
     else 
     Multiply (reduced_x, reduced_y) 
    | Divide (x, y) -> 
     let reduced_x = reduce_expr x 
     and reduced_y = reduce_expr y in 
     if both_ints reduced_x reduced_y then 
     (combine_terms div reduced_x reduced_y) 
     else 
     Divide (reduced_x, reduced_y) 
    | Term x -> Term x 

Answer 1

可以刪除both_ints，和combine_terms功能以及一些if語句，通過匹配包含操作功能內Number，如類型：

let div x y = match x,y with 
    | Number x, Number y -> Number (x/y) 
    | _ -> Divide (x,y) 

... 
let rec reduce_expr expr = match expr with 
    ... 
    | Divide (x,y) -> div (reduce_expr x) (reduce_expr y) 
    ...