expr/operator-dot.go

// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
// All rights reserved.

// operator-dot.go
package expr

import "fmt"

// -------- dot term
func newDotTerm(tk *Token) (inst *term) {
	return &term{
		tk:       *tk,
		children: make([]*term, 0, 2),
		position: posInfix,
		priority: priDot,
		evalFunc: evalDot,
	}
}

func evalDot(ctx ExprContext, self *term) (v any, err error) {
	var leftValue, rightValue any

	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
		return
	}

	indexTerm := self.children[1]

	if isList(leftValue) {
		var index int
		if index, err = indexTerm.toInt(rightValue, "index expression value must be integer"); err != nil {
			return
		}

		list, _ := leftValue.([]any)
		if index >= 0 && index < len(list) {
			v = list[index]
		} else if index >= -len(list) {
			v = list[len(list)+index]
		} else {
			err = indexTerm.Errorf("index %v out of bounds", index)
		}
	} else if isString(leftValue) {
		var index int
		if index, err = indexTerm.toInt(rightValue, "index expression value must be integer"); err != nil {
			return
		}

		s, _ := leftValue.(string)
		if index >= 0 && index < len(s) {
			v = string(s[index])
		} else if index >= -len(s) {
			v = string(s[len(s)+index])
		} else {
			err = indexTerm.Errorf("index %v out of bounds", index)
		}
	} else if isDict(leftValue) {
		var ok bool
		d, _ := leftValue.(map[any]any)
		if v, ok = d[rightValue]; !ok {
			err = fmt.Errorf("key %v does not belong to the dictionary", rightValue)
		}
	} else {
		err = self.errIncompatibleTypes(leftValue, rightValue)
	}
	return
}

// init
func init() {
	registerTermConstructor(SymDot, newDotTerm)
}