Wrong `read` function used for #lang repltest datalog

```
#lang repltest datalog
parent(amy, anabella).
parent(john, anabella).
parent(anabella, jack).
parent(jack, ted).

grandparent(X, Z) :- parent(X, Y), parent(Y, Z).

> grandparent(X, ted)?
grandparent(anabella, ted).
```

This gives the error:

```
read: illegal use of `.'
```
