Add AST package: Node interface, NumberLit, BinaryExpr

- Sealed Node interface with unexported marker method
- NumberLit holds float64 value
- BinaryExpr holds Op (token.Type), Left and Right children
- Tests verify interface satisfaction, data integrity, and nesting
2 files changed
tree: ee34b43689463e1ed0bc533aff7ca4ce6b2c0045
  1. ast/
  2. cmd/
  3. docs/
  4. lexer/
  5. token/
  6. go.mod