Grammar feedback

[multimeric]

• Some of the utility functions you're using in pipelines already exist in magrittr: https://magrittr.tidyverse.org/reference/aliases.html#details
• Manipulating source code as text can generally be replaced by utilities such as base::substitute or the tidyverse way
• Braces { around a single expression don't inherently do anything. ie { 1 } is the same as 1. So some code could be simplified without braces
• This is a very general suggestion, but note that you don't need to write out a targets workflow explicitly using tar_target(). You can actually write out abstract target factories to _targets.R which might give you more control if you need it. More info here: https://wlandau.github.io/targetopia/contributing.html. For example, the user might actually put the HPC grammar in the _targets.R and you use target factory magic to generate the real targets on demand.
• In terms of tiering, I feel sure there must be a way to avoid duplicating the whole pipeline. One thought I had is that you could make a crew controller similar to the built-in controller group, but with a custom function that selects a controller based on the tiering somehow: https://github.com/wlandau/crew/blob/4acbfe34ca51322d1418c42d38f9db88bcee0c84/R/crew_controller_group.R#L107-L115. Another thoughts is that you could use target factories to make $n$ copies of each target inside the same pipeline, and connect them all together within a tier. Target factories are still simple and clean from the user's perspective.