the function call procedure now check the number of actual parameters against the numer of formal parameters

ast.go

@@ -63,7 +63,7 @@ func (self *ast) addToken2(tk *Token) (t *term, err error) {
 	if t = newTerm(tk, nil); t != nil {
 		err = self.addTerm(t)
 	} else {
-		err = tk.Errorf("No term constructor for token %q", tk.String())
+		err = tk.Errorf("unexpected token %q", tk.String())
 	}
 	return
 }

ast_test.go

@@ -44,7 +44,7 @@ func TestAddTokensBad(t *testing.T) {
 func TestAddUnknownTokens(t *testing.T) {
 	tk0 := NewToken(0, 0, SymPercent, "%")
 
-	wantErr := errors.New(`No term constructor for token "%"`)
+	wantErr := errors.New(`unexpected token "%"`)
 
 	tree := NewAst()
 	if gotErr := tree.addToken(tk0); gotErr != nil && gotErr.Error() != wantErr.Error() {

operand-func.go

@@ -6,6 +6,7 @@ package expr
 
 import (
 	"errors"
+	"fmt"
 )
 
 // -------- function call term
@@ -21,6 +22,20 @@ func newFuncCallTerm(tk *Token, args []*term) *term {
 }
 
 // -------- eval func call
+func checkFunctionCall(ctx ExprContext, name string, params []any) (err error) {
+	if info, exists := ctx.GetFuncInfo(name); exists {
+		if info.MinArgs() > len(params) {
+			err = fmt.Errorf("too few params -- expected %d, got %d", info.MinArgs(), len(params))
+		}
+		if info.MaxArgs() >= 0 && info.MaxArgs() < len(params) {
+			err = fmt.Errorf("too much params -- expected %d, got %d", info.MaxArgs(), len(params))
+		}
+	} else {
+		err = fmt.Errorf("unknown function %s()", name)
+	}
+	return
+}
+
 func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
 	ctx := cloneContext(parentCtx)
 	name, _ := self.tk.Value.(string)
@@ -34,19 +49,21 @@ func evalFuncCall(parentCtx ExprContext, self *term) (v any, err error) {
 		params[i] = param
 	}
 	if err == nil {
+		if err = checkFunctionCall(ctx, name, params); err == nil {
 			if v, err = ctx.Call(name, params); err == nil {
 				exportObjects(parentCtx, ctx)
 			}
 		}
+	}
 	return
 }
 
 // -------- function definition term
 func newFuncDefTerm(tk *Token, args []*term) *term {
 	return &term{
-		tk:       *tk,
+		tk:       *tk, // value is the expression body
 		parent:   nil,
-		children: args, // arg[0]=formal-param-list, arg[1]=*ast
+		children: args, // function params
 		position: posLeaf,
 		priority: priValue,
 		evalFunc: evalFuncDef,

operator-assign.go

@@ -29,7 +29,14 @@ func evalAssign(ctx ExprContext, self *term) (v any, err error) {
 
 	if v, err = self.children[1].compute(ctx); err == nil {
 		if functor, ok := v.(Functor); ok {
-			ctx.RegisterFunc(leftTerm.source(), functor, 0, -1)
+			var minArgs, maxArgs int = 0, 0
+
+			if funcDef, ok := functor.(*funcDefFunctor); ok {
+				l := len(funcDef.params)
+				minArgs = l
+				maxArgs = l
+			}
+			ctx.RegisterFunc(leftTerm.source(), functor, minArgs, maxArgs)
 		} else {
 			ctx.setVar(leftTerm.source(), v)
 		}

parser_test.go

@@ -160,7 +160,7 @@ func TestParser(t *testing.T) {
 		/* 138 */ {`nil`, nil, nil},
 		/* 139 */ {`null`, nil, errors.New(`undefined variable or function "null"`)},
 		/* 140 */ {`{"key"}`, nil, errors.New(`[1:8] expected ":", got "}"`)},
-		/* 141 */ {`{"key":}`, nil, errors.New(`[1:9] expected dictionary value, got "}"`)},
+		/* 141 */ {`{"key":}`, nil, errors.New(`[1:9] expected "dictionary-value", got "}"`)},
 		/* 142 */ {`{}`, map[any]any{}, nil},
 		/* 143 */ {`1|2`, newFraction(1, 2), nil},
 		/* 144 */ {`1|2 + 1`, newFraction(3, 2), nil},