ML-错误使用异常

Question

我写了一个函数来处理异常，如果我们得到了R2 = 0，I2 = 0，但是当我运行程序我得到这个错误：

operatii.ml:12: error: Type error in function application. 
    Function: = : ''a * ''a -> bool 
    Argument: (r2, 0.0) : real * real 
    Reason: Can't unify ''a to real (Requires equality type) 
Found near 
    if r2 = 0.0 then raise ImpartitorulEsteNul else 
    (
    (r2 * r1 - i1 * i2)/(r2 * r2 + i1 * i2), 
    (... * ... + ... * ...)/(... * ... + ... * ...) 
    ) 
Exception- Fail "Static Errors" raised 

这里是我的代码：

infix %%%%; 
exception ImpartitorulEsteNul; 
fun (r1,i1) %%%% (r2:real,i2:real)=if r2=0.0 andalso i2=0.0 then raise ImpartitorulEsteNul 
         else ((r2*r1-i1*i2)/(r2*r2+i1*i2),(r2*i1+i1*i2)/(r2*r2+i1*i2)); 

Answer 1

这是因为real类型的值不能被检查的平等与正常=操作。发生这种情况是因为在计算机内部如何表示浮点数，而且，老实说，这是我无法向别人解释的东西。但是，解决方案很简单。您必须使用Real.==等于运算符：

infix %%%%; 

infix ==; 

(* Import just the == function from the Real structure. *) 
(* I hope you can make sense out of this line. *) 
val op == = Real.==; 

exception ImpartitorulEsteNul; 

fun (r1,i1) %%%% (r2:real,i2:real) = 
    if r2==0.0 andalso i2==0.0 
    then raise ImpartitorulEsteNul 
    else ((r2*r1-i1*i2)/(r2*r2+i1*i2),(r2*i1+i1*i2)/(r2*r2+i1*i2));