Expressions now support function definition

ast.go

@@ -10,11 +10,15 @@ import (
 	"strings"
 )
 
+type Expr interface {
+	Eval(ctx exprContext, preset bool) (result any, err error)
+}
+
 //-------- ast
 
 type ast struct {
 	forest []*term
-	root *term
+	root   *term
 }
 
 func NewAst() *ast {
@@ -54,7 +58,7 @@ func (self *ast) addToken(tk *Token) (err error) {
 	if t := newTerm(tk, nil); t != nil {
 		err = self.addTerm(t)
 	} else {
-		err = fmt.Errorf("No term constructor for token %q", tk.String())
+		err = tk.Errorf("No term constructor for token %q", tk.String())
 	}
 	return
 }
@@ -83,23 +87,25 @@ func (self *ast) insert(tree, node *term) (root *term, err error) {
 		root = node
 		tree.setParent(node)
 	} else {
-		err = fmt.Errorf("two adjacent operators: %q and %q", tree, node)
+		err = node.Errorf("two adjacent operators: %q and %q", tree, node)
 	}
 	return
 }
 
 func (self *ast) Finish() {
-        if self.root == nil && self.forest != nil && len(self.forest) >= 1 {
-                self.root = self.forest[len(self.forest)-1]
-                self.forest = self.forest[0:len(self.forest) - 1]
-        }
+	if self.root == nil && self.forest != nil && len(self.forest) >= 1 {
+		self.root = self.forest[len(self.forest)-1]
+		self.forest = self.forest[0 : len(self.forest)-1]
+	}
 }
 
-func (self *ast) Eval(ctx exprContext) (result any, err error) {
+func (self *ast) Eval(ctx exprContext, preset bool) (result any, err error) {
 	self.Finish()
 
 	if self.root != nil {
-		initDefaultVars(ctx)
+		if preset {
+			initDefaultVars(ctx)
+		}
 		if self.forest != nil {
 			for i, root := range self.forest {
 				if result, err = root.compute(ctx); err == nil {
@@ -121,7 +127,7 @@ func (self *ast) Eval(ctx exprContext) (result any, err error) {
 
 // Preset variables
 const (
-	preset_last_result = "_last"
+	preset_last_result   = "_last"
 	preset_bool_shortcut = "_bool_shortcut"
 )