moved a subset of source file to the kern package

kern/control.go

@@ -0,0 +1,63 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// control.go
+package kern
+
+import "strings"
+
+// Preset control variables
+const (
+	ControlPreset        = "_preset"
+	ControlLastResult    = "last"
+	ControlBoolShortcut  = "_bool_shortcut"
+	ControlSearchPath    = "_search_path"
+	ControlParentContext = "_parent_context"
+	ControlStdout        = "_stdout"
+)
+
+// Other control variables
+const (
+	ControlExportAll = "_export_all"
+)
+
+// Initial values
+const (
+	init_search_path = "~/.local/lib/go-pkg/expr:/usr/local/lib/go-pkg/expr:/usr/lib/go-pkg/expr"
+)
+
+func CtrlIsEnabled(ctx ExprContext, name string) (status bool) {
+	var v any
+	var exists bool
+
+	if !strings.HasPrefix(name, "_") {
+		name = "_" + name
+	}
+
+	if v, exists = ctx.GetVar(name); !exists {
+		if globalCtx := ctx.GetGlobal(); globalCtx != nil {
+			v, exists = globalCtx.GetVar(name)
+		}
+	}
+
+	if exists {
+		if b, ok := v.(bool); ok {
+			status = b
+		}
+	}
+	return
+}
+func SetCtrl(ctx ExprContext, name string, value any) (current any) {
+	current, _ = ctx.GetVar(name)
+	ctx.UnsafeSetVar(name, value)
+	return
+}
+
+func InitDefaultVars(ctx ExprContext) {
+	if _, exists := ctx.GetVar(ControlPreset); exists {
+		return
+	}
+	ctx.UnsafeSetVar(ControlPreset, true)
+	ctx.UnsafeSetVar(ControlBoolShortcut, true)
+	ctx.UnsafeSetVar(ControlSearchPath, init_search_path)
+}