On Sun, Jan 20, 2019 at 4:31 PM Jeremy Ruston <[email protected]>
wrote:
> Hi Joe
>
> As you've discovered macro calls don't nest. It's intentional: for the
> shorthand syntax we prefer conciseness over flexibility.
>
> <<macroname param-one:"alpha" param-two:"beta">>
>
> is actually sugar for
>
> <$macrocall $name="macroname" param-one="alpha" param-two="beta"/>
>
Now you tell me :-)
>
> With the full widget syntax you can then do things like this:
>
> <$macrocall $name="macroname" param-one=<<my-other-macro "something">>
> param-two="beta"/>
>
> If you want to pass the wikified output of one macro to another then you'd
> need to use the wikify widget.
>
>
I'd wondered why.
I think this point needs emphasising - coming from virtually
any programming langage one expects that function calls
to be nestable the BIG surprise was that "<<" ">>" didn't have to be
properly balanced and that the scope of the macro was not what I thought it
was.
I guess this is not changable now - since it would break
all old macros.
Actually to make macros composable it would be
very nice to pipe the output of the first macro into a second.
This is done in the language 'elixir' using the notatation '|>'
to represent a pipe operator.
In TW you could think of writing:
<<macro1 .. args>> |> <<macro2 arg1 arg2>>
which means take the output of <<macro1 ... args>>
stick it into a temporary variable (say t1) then evaluate
<<macro2 t1 arg1 arg2>>
The pipe operator injects the result of the first macro into the
first argument of the second macro.
This is actually very nice - since it eliminates nested function calls.
So things like:
f(g(h(i(X))) become pipes like this:
i(X) |> h |> g |> f
And I guess it would not break old code - since old code would
never have used a |> symbol :-)
I'm not sure if this is possble - but a pipe notation often beats
nested function calls for simplicity :-)
And pipes are nice as abstractions for different reasons.
Cheers
/Joe
> Best wishes
>
> Jeremy
>
>
> --
> Jeremy Ruston
> [email protected]
> https://jermolene.com
>
> On 19 Jan 2019, at 19:59, Joe Armstrong <[email protected]> wrote:
>
>
> I have two macros
>
> \define text()
> A line of text
> \end
>
> \define foo(x)
> fooStart $x$ fooStop
> \end
>
> So
>
> <<text>> is replaced by "A line of text"
>
> and
>
> <<foo "abc">> is replaced by "Start abc fooStop"
>
> But <<foo <<text>> >>
>
> is replaced by "fooStart <<text fooStop >>"
>
> And NOT "fooStart A line of text fooStop" as I had expected.
>
> After a lot of head scratching I realised that this means that the
> argument (x) to foo is the
> string "<<text" ie the first occurrence of ">>" to the left
> of the start "<<" of the macro and not the second occurrence.
>
> ie. "<<" and ">>" do not properly nest as I had expected.
>
> This seems like a pretty big pothole for a beginner to fall into ...
>
> So what is the accepted idiom for using a macro result
> as the input argument to another macro - how does one chain macro calls
> together?
>
> Cheers
>
> /Joe
>
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