Defining a function in f#

Question

In F# I can define a function like this

let (-+->) x y = x + y

and call like this

let z =  5 -+-> 6

I can even do something like this

let (-++->) x y z = x y z
let p = ((fun x -> fun y -> x + y) -++-> 5 ) 6

But why can't I do this?

let (nafis) x y = x + y
let p = 5 nafis 6

it gives me this error Unexpected identifier in binding. Expected '=' or other token.

Are functions like let (-+->) x y = x + y any special kind of function?

Answer 1

F＃规范中定义了对运算符的词汇约束：

3.7符号运算符

用户定义和库定义的符号运算符是如下所示的字符序列，除非字符序列是符号关键字（第3.6节）。

regexp first-op-char= !%&*+-./<=>@^|~
regexp op-char= first-op-char | ?
token quote-op-left = 
  | <@ <@@ 
token quote-op-right =  
  | @> @@> 
token symbolic-op= 
  | ?
  | ?<-
  | first-op-charop-char* 
  | quote-op-left
  | quote-op-right

如您所见，-++->有效，而nafis无效。