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我正在写一个简单的小型ocaml程序,它从文件中读取代数语句,使用ocamllex/ocamlyacc将其解析为AST,将其缩小并打印出来。我减少表情的部分似乎有点......很难看。有什么办法可以简化它吗?如何简化这个ocaml模式匹配代码?
(* 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
注意ocaml的确实需要的算术运算符作为函数:使用(/),(+)(*)和( - )...该()是强制性的,该空间只强制用于* – 2009-12-02 17:46:31
仅供分析之用,menhir值得考虑。 http://cristal.inria.fr/~fpottier/menhir/ – LB40 2009-12-03 13:42:18
其实,我一直在使用ocamlyacc,通常我会使用menhir,但是我想保持简单的依赖。 – 2009-12-03 14:43:43