Expressions in Janis

[illusional]

The more complex workflows that we build, the more we've felt the feed for some mechanism to transform some value at runtime. in CWL, this could be a Javascript expression in a valueFrom box. In WDL this would be functions available within the Standard Library.

Essentially, we can define some "Operator" class, and override all the python operations to build up a tree of operations. When we translate to CWL / WDL, we can unwind these expressions, and operators will have a standard library or Javascript equivalent.

The ground work for it has been tested here: PMCC-BioinformaticsCore/janis-core#5, but I think it'll be worth pulling it out separately.

This is an addition to the language and should be backwards compatible.

For example:

wf.input("inp1", int, value=1)
wf.input("inp2, str, value="Hi")


wf.inp1 > 2  #  GreaterThanOperator(InputSelector("inp1") > 2)
to_upper_case(wf.inp2) == "HI" # EqualityOperator(UpperCaseOperator(InputSelector("inp2")), "HI")

Backwards compatibility

This might change the structure of some input bindings on CWL, depending on where the expressions are used, however no code changes should be required, as it's an introduction to the Janis API.