But why would someone use a new DSL, vs an existing (general-purpose-ish) language that supports numerics (there are enough out there, e.g. R, Python, or the nu

But why would someone use a new DSL, vs an existing (general-purpose-ish) language that supports numerics (there are enough out there, e.g. R, Python, or the numerous paid ones like matlab, mathematica or IDL)? You have no ecosystem, plus now you're got to wrap 50+ years of numerical libraries...