opexpr

type Element interface {
	// ParenKind returns an integer representing the 'kind' of parenthesis. For
	// example, by assigning different kinds to '()' and '[]' you can require that
	// opening and closing parentheses are appropriately matched. Its value is
	// applicable only for OpenParen, CloseParen and CloseAllParens elements.
	ParenKind() int
	// ExpressionKind returns a value representing the kind of the expression (see
	// docs for ExpressionKind). The boolean argument is true when the expression
	// has a value to its left. This makes it possible to handle operators that
	// can be either prefix or postfix, or operators that can be either binary or
	// unary.
	ExpressionKind(hasExpressionToLeft bool) ExpressionKind
	// Precedence returns an integer representing the operator's precedence
	// relative to other operators. Lower values indicate higher precedence (i.e.
	// operators that bind tighter). The boolean argument is true when the
	// expression has a value to its left. This makes it possible to handle
	// operators that can be either prefix or postfix, or operators that can be
	// either binary or unary.
	Precedence(hasExpressionToLeft bool) int
}

type ExpressionKind int

type ParseError[EP Element] struct {
	Kind ParseErrorKind
	Elem EP
}

type ParseErrorKind int

type SimpleNode[T Element] struct {
	Left, Right *SimpleNode[T]
	Value       T
}

type StringElement string

type TreeBuilder[T any, E Element] interface {
	Element
	// Given that the receiver is an operator or an opening parenthesis, make a
	// corresponding parse tree node with the specified children. Either or both
	// of leftArg and rightArg may be nil depending on the arity and
	// prefix/postfix nature of the operator. If the receiver is an opening
	// parenthesis then leftArg is non-nil and rightArg is nil.
	MakeNode(leftArg, rightArg *T) *T
	// MakeErrorNode makes an error node given a parse error and left/right
	// children (either or both of which may be nil).
	MakeErrorNode(pe *ParseError[E], leftChild, rightChild *T) *T
}