From 6d8c6f5154af5c4fe9fd55e9022123209d2f9675 Mon Sep 17 00:00:00 2001
From: Celestino Amoroso <celestino.amoroso@gmail.com>
Date: Thu, 28 Mar 2024 06:32:37 +0100
Subject: [PATCH] helpers.go provides easy functions to parse and evaluate
 expressions

---
 helpers.go | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 helpers.go

diff --git a/helpers.go b/helpers.go
new file mode 100644
index 0000000..f62e5f7
--- /dev/null
+++ b/helpers.go
@@ -0,0 +1,57 @@
+// helpers.go
+package expr
+
+import (
+	"fmt"
+	"strings"
+)
+
+func EvalString(ctx exprContext, source string) (result any, err error) {
+	var tree *ast
+
+	r := strings.NewReader(source)
+	scanner := NewScanner(r, DefaultTranslations())
+	parser := NewParser(ctx)
+
+	if tree, err = parser.parse(scanner); err == nil {
+		result, err = tree.eval(ctx)
+	}
+	return
+}
+
+type EvalArg struct {
+	name  string
+	value any
+}
+
+func EvalStringA(source string, args ...EvalArg) (result any, err error) {
+	return EvalStringV(source, args)
+}
+
+func EvalStringV(source string, args []EvalArg) (result any, err error) {
+	ctx := NewSimpleFuncStore()
+	for _, arg := range args {
+		if isFunc(arg.value) {
+			if f, ok := arg.value.(FuncTemplate); ok {
+				ctx.addFunc(arg.name, f)
+			} else {
+				err = fmt.Errorf("invalid function specification: %q", arg.name)
+			}
+		} else if integer, ok := anyInteger(arg.value); ok {
+			ctx.SetValue(arg.name, integer)
+		} else if float, ok := anyFloat(arg.value); ok {
+			ctx.SetValue(arg.name, float)
+		} else if _, ok := arg.value.(string); ok {
+			ctx.SetValue(arg.name, arg.value)
+		} else if _, ok := arg.value.(bool); ok {
+			ctx.SetValue(arg.name, arg.value)
+		} else {
+			err = fmt.Errorf("unsupported type %T specified for item %q", arg.value, arg.name)
+		}
+	}
+
+	if err == nil {
+		result, err = EvalString(ctx, source)
+	}
+	return
+}