[jasperry]

Syntax comment: in your control structures you use a keyword ("do", "then") to start a block as well as wrapping the block in parentheses. This feels superfluous. I suggest sticking with either keywords or parens to delineate blocks, not both.

[jcparkyn]

This is a little bit tricky because the parser has to distinguish between:

  for x in arr (something ())
           \                 /-- function call

and

  for x in arr (something ())
               \            /-- loop body

This is consequence of combining "blocks" and "precedence" into the same construct ().

A more fitting example would be to support:

  for x in arr do set z += x;
  for x in arr do something x;

IIRC these both currently require an explicit block in my parser.

[jasperry]

I see, thanks for the clear example of the ambiguity you need to avoid! Fun stuff.