Re: [isabelle] Type as argument
With the example, would it be possible to let f be a parameter of a locale
locale A1 =
fixes f :: "nat => 'a itself => bool"
defines "fs (t::nat itself) = (if s = a then True else False)"
complains about the operand "t::nat itself". Is it asking for "nat" to be a
On May 16, 2011 3:53pm, Brian Huffman <brianh at cs.pdx.edu> wrote:
2011/5/16 Steve W s.wong.731 at gmail.com>:
> Thanks all. One more question: what is the "itself" keyword for in "'a
The "itself" is just a type constructor. It is like what you would get
from the following datatype declaration:
datatype 'a itself = Type (* one constructor with no arguments *)
The syntax "TYPE('a)" is an abbreviation for "Type :: 'a itself".
> 2011/5/13 René Thiemann rene.thiemann at uibk.ac.at>
>> > Thanks. If I change f to a binary function:
>> > class foo =
>> > fixes f :: "int => 'a itself => int"
>> > and with the following instantiation:
>> > instantiation nat :: foo
>> > begin
>> > definition "f 0 (t::nat itself) = 0"
>> > instance ..
>> > end
>> > I get an error on "0::int". It works if 0 is replaced by a free
>> > though. Why's that?
>> Because "definition" cannot be used with pattern matching on left-hand
>> Usually, one can use "fun" instead. However, even with "fun" you cannot
>> do pattern matching on "int" instead of "nat".
>> However, you might write "fx (t:: nat itself) = (if x = (0 :: int)
>> else ...)"
>> René Thiemann mailto:rene.thiemann at uibk.ac.at
>> Computational Logic Group
>> Institute of Computer Science phone: +43 512 507-6434
>> University of Innsbruck
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