Eprx now supports range of indeces to extract parts of strings or lists

operator-range.go

@@ -0,0 +1,69 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-range.go
+package expr
+
+import "fmt"
+
+// -------- range term
+type intPair struct {
+	a, b int
+}
+
+func (p *intPair) TypeName() string {
+	return typePair
+}
+
+func (p *intPair) ToString(opt FmtOpt) string {
+	return fmt.Sprintf("(%d, %d)", p.a, p.b)
+}
+
+func isIntPair(v any) bool {
+	_, ok := v.(*intPair)
+	return ok
+}
+
+func newRangeTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priDot,
+		evalFunc: evalRange,
+	}
+}
+
+func evalRange(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	// if err = self.checkOperands(); err != nil {
+	// 	return
+	// }
+	if len(self.children) == 0 {
+		leftValue = int64(0)
+		rightValue = int64(-1)
+	} else if len(self.children) == 1 {
+		if leftValue, err = self.children[0].compute(ctx); err != nil {
+			return
+		}
+		rightValue = int64(-1)
+	} else if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+	if !(IsInteger(leftValue) && IsInteger(rightValue)) {
+		err = self.errIncompatibleTypes(leftValue, rightValue)
+		return
+	}
+
+	startIndex, _ := leftValue.(int64)
+	endIndex, _ := rightValue.(int64)
+
+	v = &intPair{int(startIndex), int(endIndex)}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymColon, newRangeTerm)
+}