Re: EXTERNAL: [vhdl-200x] VHDL ternary operation

Thanks Jim, Mike, and Andy.

Yes, I could write a function, though I still hope that there's something I
could use out-of-the-box from the standard.

I like that "function with anonymous types" idea. So I could write:
cond(fault,"pass","fail");

However, I was also thinking of using inline operators (so that at first
glance, the intent becomes clear).
Have we in the past explored the possibility of introducing inline ternary
operators (similar to Verilog)?
fault ? "pass" : "fail"

or at least something like:
fault ? ("pass", "fail")

where the "function with anonymous type" could be defined as:
function "?"(sel:boolean; t,f: anonymous) return anonymous;

and could be a generic subprogram.

Perhaps even the following makes sense:
function "?"(sel:boolean; din_vectors: anonymous_vector) return anonymous;

So we could use it like this:
fault ? ("pass", "fail")

As was mentioned, when-else can only be used for conditional assignments,
which I feel is too limiting. Can its use be extended to expressions as
well (how feasible is it for a tool vendor)?

Or perhaps we could explore (or re-explore) the possibility of having
inline ternary operators that can be used in many ways, including
conditional assignments and expressions.

Just my 2 cents.

regards, daniel

On 29 March 2013 23:48, Mike Treseler <mtreseler@gmail.com> wrote:

> On Thu, Mar 28, 2013 at 7:40 AM, Jones, Andy D <andy.d.jones@lmco.com>
> wrote:
> > Daniel,
> >
> >
> >
> > "pass" when fault else "fail" is NOT an expression. It is the RHS of a
> > conditional assignment statement. Such a RHS may contain expressions, but
> > expressions may not contain a conditional assignment RHS.
> >
> >
> >
> > Since conditional assignments can be open-ended, in effect meaning that
> the
> > assignment does not occur if no “when” expression evaluates as true, its
> use
> > as an expression is not possible.
> >
> >
> >
> > To solve your immediate problem, you could write a function that takes a
> > boolean argument and returns “pass” or “fail” strings, or you could
> create a
> > constant array of two strings, indexed by boolean, e.g. (true => “fail”,
> > false => “pass”). Then you could include the function call or constant in
> > your report expression.
>
> It's a hard problem. 'Just write function' is good advice. -- MT
>
>
> ------------------------------------------------------------------------------
>    function sel (                                  -- sel(false,a,b) => a
>       choice : boolean;                         -- sel( true,a,b) => b
>       t, f   : std_logic_vector)                -- works like  "arg ? a:b"
>       return std_logic_vector
>    is
>    begin
>       if choice then return t; else return f; end if;
>    end function sel;
>
>
> ------------------------------------------------------------------------------
>    function push (                        -- Push byte into word, uses
> sel()
>       byte       : in std_logic_vector;
>       word       : in std_logic_vector;
>       shift_left : in boolean := true)  -- left is default
>       return std_logic_vector
>    is  -- push byte into word from left or right
>       variable byte_v :  std_logic_vector(byte'length-1 downto 0) := byte;
>       variable word_v : std_logic_vector(word'length-1 downto 0) := word;
>    begin
>       return(
>          sel(                    -- select value for true or false
>             choice => shift_left,
>             t =>              word_v(word_v'left - byte'length downto
> 0) & byte_v,
>             f => byte_v & word_v(word_v'left     downto byte'length))
>          );
>    end function push;
> >
> >
> > Andy
> >
> >
> >
> > From: owner-vhdl-200x@eda.org [mailto:owner-vhdl-200x@eda.org] On
> Behalf Of
> > Daniel Kho
> > Sent: Thursday, March 28, 2013 4:19 AM
> > To: vhdl-200x@eda.org
> > Subject: EXTERNAL: [vhdl-200x] VHDL ternary operation
> >
> >
> >
> > Hi all,
> >
> > I'm wondering if the current revision supports something like the
> following?
> >
> > report to_hstring(index) & ", " & ("pass" when fault else "fail") & lf &
> > nul;
> >
> > where "index" is an unsigned vector, and "fault" is a boolean.
> >
> >
> >
> > The expression ("pass" when fault else "fail") can already be used
> directly
> > in clocked processes, but I'm not too sure if the standard allows this
> to be
> > used within report statements.
> >
> > If there's a better way of writing which could produce the same effect,
> do
> > share with me as well.
> >
> >
> >
> > regards, daniel
> >
> >
> > --
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