Struct binary

ch7/eval/ast.go:29–32

A binary represents a binary operator expression, e.g., x+y.

// A binary represents a binary operator expression, e.g., x+y.
type binary struct {
	op   rune // one of '+', '-', '*', '/'
	x, y Expr
}

// A call represents a function call expression, e.g., sin(x).
type call struct {