Coerce a value to the type referenced by a symbol. By default supports Int and Str.

Resolve an environment variable by name. Optionally accepts a type for coercion, and a keyword option, :or, that provides a default value if the environment variable is missing.

The arguments may optionally be wrapped in a vector. This is to support their use in duct.core/read-config. For example:

{:port #env ["PORT" Int :or 3000]}