ivy: simplify (and correct) code for opdelete

Was missing a check for EOF. Also, I didn't trust where it was
being done: too much state already built. None of it is needed.

Also add execution failure tests for bad opdeletes.

exec/context.go

@@ -233,28 +233,25 @@ func (c *Context) Define(fn *Function) {
 	c.Defs = append(c.Defs, OpDef{fn.Name, fn.IsBinary})
 }
 
-func (c *Context) UnDefine(fn *Function) {
-	binary := false
-	ary := "unary"
-	if fn.IsBinary {
-		binary = true
-		ary = "binary"
-	}
+func (c *Context) Undefine(name string, binary bool) {
 	// Is it already defined?
 	for i, def := range c.Defs {
-		if def.Name == fn.Name && def.IsBinary == fn.IsBinary {
+		if def.Name == name && def.IsBinary == binary {
 			// Yes. Drop it.
 			c.Defs = append(c.Defs[:i], c.Defs[i+1:]...)
 			if binary {
-				delete(c.BinaryFn, fn.Name)
+				delete(c.BinaryFn, name)
 			} else {
-				delete(c.UnaryFn, fn.Name)
+				delete(c.UnaryFn, name)
 			}
 			return
 		}
 	}
-
-	value.Errorf("no definition for %s %s", ary, fn.Name)
+	ary := "unary"
+	if binary {
+		ary = "binary"
+	}
+	value.Errorf("no definition for %s %s", ary, name)
 }
 
 // noVar guarantees that there is no global variable with that name,

parse/function.go

@@ -42,7 +42,12 @@ func (p *Parser) functionDefn() {
 	if p.peek().Type == scan.Identifier {
 		idents = append(idents, p.next().Text)
 	}
-	tok := p.next()
+	// Undefine if so requested.
+	if undefine {
+		p.need(scan.EOF)
+		p.context.Undefine(idents[len(idents)-2], len(idents) == 3)
+		return
+	}
 	// Install the function in the symbol table so recursive ops work. (As if.)
 	var installMap map[string]*exec.Function
 	if len(idents) == 3 {
@@ -65,12 +70,6 @@ func (p *Parser) functionDefn() {
 	if fn.Name == fn.Left || fn.Name == fn.Right {
 		p.errorf("argument name %q is function name", fn.Name)
 	}
-	// Undefine if so requested.
-	if undefine {
-		p.context.UnDefine(fn)
-		p.need(scan.EOF)
-		return
-	}
 	// Define it, but prepare to undefine if there's trouble.
 	prevDefn := installMap[fn.Name]
 	p.context.Define(fn)
@@ -86,6 +85,7 @@ func (p *Parser) functionDefn() {
 		}
 	}()
 
+	tok := p.next()
 	switch tok.Type {
 	case scan.Assign:
 		// Either one line:

testdata/exec_fail.ivy

@@ -57,3 +57,9 @@ op inc b =
 
 inc 1
 	X
+
+# no definition for unary foo
+opdelete foo
+
+# no definition for binary foo
+opdelete x foo y