Expressions now support function definition

operand-func.go

@@ -4,8 +4,13 @@
 // operand-func.go
 package expr
 
-// -------- function term
-func newFuncTerm(tk *Token, args []*term) *term {
+import (
+	"errors"
+	"fmt"
+)
+
+// -------- function call term
+func newFuncCallTerm(tk *Token, args []*term) *term {
 	return &term{
 		tk:       *tk,
 		class:    classVar,
@@ -14,12 +19,12 @@ func newFuncTerm(tk *Token, args []*term) *term {
 		children: args,
 		position: posLeaf,
 		priority: priValue,
-		evalFunc: evalFunc,
+		evalFunc: evalFuncCall,
 	}
 }
 
-// -------- eval func
-func evalFunc(ctx exprContext, self *term) (v any, err error) {
+// -------- eval func call
+func evalFuncCall(ctx exprContext, self *term) (v any, err error) {
 	name, _ := self.tk.Value.(string)
 	params := make([]any, len(self.children))
 	for i, tree := range self.children {
@@ -34,3 +39,59 @@ func evalFunc(ctx exprContext, self *term) (v any, err error) {
 	}
 	return
 }
+
+// -------- function definition term
+func newFuncDefTerm(tk *Token, args []*term) *term {
+	return &term{
+		tk:       *tk,
+		class:    classVar,
+		kind:     kindUnknown,
+		parent:   nil,
+		children: args, // arg[0]=formal-param-list, arg[1]=*ast
+		position: posLeaf,
+		priority: priValue,
+		evalFunc: evalFuncDef,
+	}
+}
+
+// -------- eval func def
+// TODO
+type funcDefFunctor struct {
+	params []string
+	expr   Expr
+}
+
+func (functor *funcDefFunctor) Invoke(parentCtx exprContext, name string, args []any) (result any, err error) {
+	ctx := parentCtx.Clone()
+	for i, p := range functor.params {
+		if i < len(args) {
+			ctx.SetValue(p, args[i])
+		} else {
+			ctx.SetValue(p, nil)
+		}
+	}
+	result, err = functor.expr.Eval(ctx, false)
+	return
+}
+
+func evalFuncDef(ctx exprContext, self *term) (v any, err error) {
+	bodySpec := self.value()
+	if expr, ok := bodySpec.(*ast); ok {
+		paramList := make([]string, 0, len(self.children))
+		for i, param := range self.children {
+			if paramName, ok := param.value().(string); ok {
+				paramList = append(paramList, paramName)
+			} else {
+				err = fmt.Errorf("invalid function definition: formal param nr %d must be an identifiers", i+1)
+				break
+			}
+		}
+		v = &funcDefFunctor{
+			params: paramList,
+			expr:   expr,
+		}
+	} else {
+		err = errors.New("invalid function definition: the body specification must be an expression")
+	}
+	return
+}