Re: [Hol-info] A question about the definition of the function in HOL4

[Ramana K. <Ram...@cl...>]

Hi Ada,

It still looks like you might be mixing up ML and HOL. Are you trying to
define an ML function, or a HOL function?

In ML, the conjunction of two Boolean expressions can be formed using the
"andalso" operator.
Now, maybe you already defined /\ like this, and gave it infix status:

infix /\;
fun op /\ (a, b) = a andalso b;

Then I would expect your definition to work.

But please note that this is a definition in ML. If you want to make a
definition in HOL, use Define.
For example:

val ccdd_def = Define`ccdd a b c d = if ((a = b) /\ (c = d)) then T else F`;

Cheers,
Ramana


On 30 June 2016 at 22:51, Ada <956...@qq...> wrote:

>     Hi,guys
>     I am working with HOL4.
>     I defined a function in HOL4,like following
>     - fun ccdd a b c d  = if ((a = b) /\ (c = d)) then true else false;
>     It responded that:
>     ! Toplevel input:
>     ! fun ccdd a b c d  = if ((a = b) /\ (c = d)) then true else false;
>     !                         ^^^^^^^
>     ! Type clash: expression of type
>     !   bool
>     ! cannot have type
>     !   'a -> 'b
>     I can't understand it.
>     Who know the reason?
>         Thanks!
>
>
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