Drop unused, commented-out line.
Add DAG for conditionals.
Compress the output representation of a fn type.

The representation '(int, string) => bool' has spaces that break up the type, making it slightly unclear that the bits are all part of a whole. Reduce spaces to be slightly uglier but a lot more unified / clear / Gestalt.
Trivial: colour '=' in default parameter string.
Hook up parsing support for default parameters.

We actually had support in the Parser class, we just didn't tell byacc about it.
More detailed output from ast::Action, dag::Build;
Drop now-duplicate dag::Value::str().

Since Printable knows how to generate str() from PrettyPrint, this is now redundant.
We should complain about positional-after-keyword.
in:file and out:file is an ok action parameter.
Specify if an action takes a file, not list[file].