Spec. for anonymous functions with by-value parameters is not implemented

[scabug]

In the specification, a function type with by-value paramters is defined as such:

Type ::= ‘(’ [‘=>’ Type] ‘)’ ‘=>’ Type
       | ...

In practice, the compiler accepts types such as:

(=>int, =>int) => int

It is a bit tricky to have the specification fit the implementation properly because the grammar for a non-by-value parameter list is part of SimpleType (and shares a production with tuple types):

SimpleType ::= ‘(’ Types [‘,’] ’)’
            | ...

Wich means the by-value marker => cannot be added there.

It isn't pretty, but the rule for Type may be changed to:

Type ::= ‘(’ [‘=>’ Type {‘,’ [‘=>’] Type}] ‘)’ ‘=>’ Type
       | ...

This issue is a sub-element of #233.

This issue is related to #238.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-241?orig=1
Reporter: @dubochet
See #233, #238

[scabug]

@dubochet said:
This is a known issue, but specifying it (not only in the syntax) is quite subtle. For now, we specify the simple, one parameter behaviour. The rest is unspecified implementation.

[scabug]

@harrah said:
For the record, the syntax part was updated in r22045.

[som-snytt]

As specified, except ParamType includes repeated parameters.

scala> val f: (=> Int, => Int) => Int = null
val f: (=> Int, => Int) => Int = null

scala> val f: (=> Int, Int*) => Int = null
                           ^
       error: repeated parameters are only allowed in method signatures; use Seq instead