为什么我的 scala 函数/闭包定义是非法的？[已结束]

问：

我正在学习 scala 编程语言。

这里有一些简单的功能和带有错误的闭包，请帮我修复它们：Rational.scala

// function

def f11(a:Int, b:Int):Int { return a+b; }                          

def f12(a:Int, b:Int):Int = a+b                                   
def f21(a:(Int)=>Int, b:Int):Int { return a(b); }                  

def f22(a:(Int)=>Int, b:Int):Int = a(b)                            

def f31(a:Int, b:Int):(Int)=>Int { return (c:Int) => a + b + c; }  

def f32(a:Int, b:Int):(Int)=>Int = (c:Int) => a + b + c            

// closure

val g11 = (a:Int, b:Int) => a + b;                                  

val g12:(Int,Int)=>Int = (a:Int, b:Int) => { return a + b; }       

val g21 = (a:(Int)=>Int, b:Int) => a(b);                           

val g22:((Int)=>Int,Int)=>Int = (a:(Int)=>Int, b:Int) => { return a(b); }

val g31 = (a:Int, b:Int) => (c:Int) = a+b+c;            

val g32:(Int,Int)=>(Int)=>Int = (a:Int, b:Int) => { return (c:Int) => a+b+c; }

运行它们时，给我错误消息：scala Rational.scala

Rational.scala:32: error: illegal start of declaration (possible cause: missing `=` in front of current method body)
def f11(a:Int, b:Int):Int { return a+b; }                          // (Int,Int)->Int
                            ^
Rational.scala:36: error: illegal start of declaration (possible cause: missing `=` in front of current method body)
def f21(a:(Int)=>Int, b:Int):Int { return a(b); }                  // ((Int)->Int,Int)->Int
                                   ^
Rational.scala:40: error: illegal start of declaration (possible cause: missing `=` in front of current method body)
def f31(a:Int, b:Int):(Int)=>Int { return (c:Int) => a + b + c; }  // (Int,Int)->(Int)->Int
                                   ^
Rational.scala:54: error: ';' expected but '=' found.
val g31 = (a:Int, b:Int) => (c:Int) = a+b+c;