I wrote this makefile for running a lex-based program:

```
all:  getf lex

getf: gpplex
    ./gpplex $(ARGS)    

lex: gpplex
    ./gpple

lex.yy.c: gpplex.l
    flex gpplex.l

gpplex: lex.yy.c
    gcc lex.yy.c -lfl -o gpplex

clean:
    rm gpplex

```

I want to modify that such that if I run the command `make filename.txt` then the rule for `getf` will run, passing the `make` argument to the program, but if I don't specify any arguments to `make` then the `lex` target must run.

How can I achieve that?