### Parser

* `/src/parser/spider_monkey_ast.ml`: The type definitions for the AST. Tries to stay very close to ESTree
* `/src/parser/lexer_flow.mll`: The ocamllex lexer logic
* `/src/parser/parser_flow.ml`: The recursive descent JS parser

### Inference

* `/src/typing/type_inference_js.ml`: Contains the "entry point" for inference (Function called `infer_ast`).
* `/src/typing/statement.ml`: Most of the inference logic (runs through the AST and generates the initial constraints)
* `/src/typing/env_js.ml`: Most of the environment logic. An inference "env" is basically a stack of scopes -- which are defined in `scope.ml`.

### Checking/constraint solver

* `/src/typing/flow_js.ml`: Contains [the massive pattern-match](https://github.com/facebook/flow/blob/master/src/typing/flow_js.ml#L819) that defines the various rules for what to do during the "evaluation" phase when we encounter any given flow constraint. Helpful hint: Flow constraints are defined in terms of 2 types: A "lower bound" and an "upper bound". The "lower bound" is the type that flows into the "upper bound". When you see variables named `l` that often means "lower bound", and `u` often means "upper bound".