Re: Comments on process template syntax

[Roel Janssen <roel@gnu.org>]

On Sun, 2020-02-02 at 11:20 +0100, Ricardo Wurmus wrote:
> Hi,
> 
> While looking at the examples at 
> https://www.guixwl.org/beyond-started,
> I found that process templates might be difficult to understand, and
> that they have no pretty syntax.
> 
> --8<---------------cut here---------------start------------->8---
> process: (list-file-template filename)
>   name
>     string-append "list-file-"
>                   basename filename
>   packages "gzip"
>   inputs filename
>   outputs
>     string-append filename ".list"
>   run-time
>     complexity
>       space 20 mebibytes
>       time  30 seconds
>   # { gzip --list {{inputs}} > {{outputs}} }
> --8<---------------cut here---------------end--------------->8---
> 
> The first line is easy to understand for lispers but it might look
> weird
> to people who come from other workflow languages or programming
> languages.  This describes a procedure called “list-file-template”
> that
> returns a process parameterized on the argument “filename”.
> 
> Nextflow has no concept of procedures that produce processes when
> given
> arguments.  It does however have a concept of data streams that can
> be
> fed into processes, which results in a process to be instantiated for
> every element of the stream.  The stream may be created from a
> directory
> containing files.
> 
> This implementation likely stems from the realization that the
> “template
> case” is the most common case for processes.  Rarely ever is it
> necessary to define a process that does *not* require
> parameterization
> on its inputs.
> 
> Can we make the common case simpler and easier to understand?

Perhaps with some parentheses?  That it is a Lisp is a good thing, not
something you'd rather hide.. :)  Like you've said; what you've defined
above is a procedure, not a record.  That's a really cool "feature" of
the GWL!

Maybe we can just clarify the feature better in the documentation. 
Here's my initial thought:
---
When defining processes, they can be parameterized by turning the
process definition into a procedure, which will form a template for
processes to be defined later.  This is done by adding a name for the
template, and its parameters directly after "process:".
---

Kind regards,
Roel Janssen