How to conditionally select a recipe?

[donatello]

I would like to conditionally select a recipe based on argument. For example, I have a list of projects in golang, and a list of projects in rust. I want to build any one of them based on the name of the project.

I want to execute something like:

$ just build g1 # A go project
OR
$ just build r1 # A rust project.

and have just pick the right recipe. Here is what I tried - a recipe called build that selects the recipe to run (as a dependency) based on the name of the project:

export go_projects := "g1 g2 g3"
export rust_projects := "r1 r2"

build $project: if `echo $go_projects | grep -q --line-regexp $project && echo go` == "go"` {
  (build_go project)
} else if `echo $rust_projects | grep -q --line-regexp $project && echo rust` == "rust"` {
  (build_rust project)
} else {
  (bad_project_msg project)
}

build_rust $project:
    echo "Building rust project $project"

build_go $project:
    echo "Building go project $project"

bad_project_msg $project:
     echo "unknown project $project"

Obviously this doesn't work because specifying this type of conditional dependency for build is not supported. Is there an recommended way to achieve this, ideally without recursively calling just?