mutator error message for empty program unclear

[robby]

This program

#lang planet plai/plai:1:8/mutator

produces this error message

#%module-begin: bad syntax in: (#%module-begin)

but would be better if it said "expected ..." and gave me a schematic of the expression it expected to find there. Similarly, these programs all produce bad error messages:

#lang planet plai/plai:1:8/mutator
()

#lang planet plai/plai:1:8/mutator
1

#lang planet plai/plai:1:8/mutator
(a b c)

[robby]

Also, this program:

#lang planet plai/plai:1:8/mutator
(allocator-setup "no-collection-collector.ss" "y")

produces a contract error describing the wrong function:

Language: planet plai/plai:1:8/mutator custom; memory limit: 256 megabytes.
(file "/Users/robby/svn/usr/robby/pl-class/w10/gc/mutator1.ss") broke the contract

(-> exact-nonnegative-integer? void?)

on init-heap!; expected <exact-nonnegative-integer?>, given: "y"