General

• Documentation
• Tests
• CLI Options
• Branding

Internals

• Non-recursive treeify
• Tokens with impl: get line, get args, ::new
• Fix names (Root isn't sqrt!)

Features

• Function application
• variable definitons
• function definitions
• rational datatype
• units
• Dice

Prompt

• Replace multi-char tokens (pi)
• Arrows, history, live syntax check or output
• Commands
• Better error texts