analysis

type Cell struct {
	Index  int    // position among the notebook's code cells
	Source string // the cell's Go source

	Chunks []Chunk

	// Defines lists the notebook variables the cell defines: those of its
	// declarations, then those of its statements, each in order of
	// appearance. Funcs and Types are the subsets declared with func and
	// type. Imports maps a package name to its import path.
	Defines []string
	Funcs   []string
	Types   []string
	Imports map[string]string

	// Uses lists the free identifiers the cell reads, sorted: notebook
	// variables, package names other cells import, builtins, and names
	// that are not defined anywhere (the compiler reports those).
	Uses []string

	// OwnPackages lists, sorted, the names of the packages the cell imports
	// itself and refers to.
	OwnPackages []string

	// Display is the cell's final expression statement, if any, and its
	// byte range in Source.
	Display                  ast.Expr
	DisplayStart, DisplayEnd int

	// Assigns lists the free identifiers the cell assigns to (=, op=, ++,
	// --), with the offset of each assignment.
	Assigns []Use

	// Errors are syntax errors, with offsets in Source.
	Errors []Error
}

type Chunk struct {
	Decl       bool
	Start, End int // byte offsets in the cell's source
}

type Error struct {
	Cell int
	Pos  int
	Msg  string
}

type Graph struct {
	Cells []*Cell

	// Owner maps each notebook variable to the cell that defines it.
	Owner map[string]int

	// Deps[i] lists the cells cell i reads from, sorted; Dependents is the
	// reverse relation.
	Deps, Dependents [][]int

	// Order is an execution order: every cell after the cells it reads, and
	// otherwise in document order. It holds every cell when Errors is empty.
	Order []int

	// Errors lists syntax errors, names defined twice, assignments to
	// another cell's variable, and dependency cycles.
	Errors []Error
}

type Use struct {
	Name string
	Pos  int
}