COM 3355 Assignment #2.
Assigned:  Thursday, 16 January 2003
Due:       Thursday, 30 January 2003, by 5pm EST

Implement a static semantic analysis phase for quirk20 as
specified below.  This phase shall define a top-level
procedure named checkTypes that takes one argument, an
abstract syntax tree for a complete quirk20 program, and
returns that very same abstract syntax tree after checking
it for errors using the scope and type rules of quirk20,
and after performing the side effects specified below.

If checkTypes detects an error, it should call the top-level
errMsg procedure with a string that describes the error, and
should then call the top-level exit procedure with an argument
of 1.  (Neither of these procedures is part of R5RS Scheme.
The errMsg will be provided by the instructor, and the exit
procedure is provided by most implementations of Scheme.  If
your implementation does not define an exit procedure, please
define your own for testing.)

If the program contains no errors, then checkTypes returns its
argument after performing the following side effects:

    If the operation of a UnOpExp or BinOpExp node is an
    overloaded operation, then checkTypes must resolve the
    overloading by calling Ast.updateOp on the node with an
    appropriate second argument.  (This may transform the node
    into a different kind of node, so this should be the last
    action that checkTypes performs on the subtree rooted at
    that node.)

    For each NewRecordExp node, checkTypes must use Ast.update1
    on the node to store the number of dynamic fields n within
    the record being created, and must use Ast.updateInits on
    the node to store an array of n integers that encode the
    type of each of the dynamic fields, using the encodings
    defined in qtype.Qtype, e.g. Qtype.iDoubleType.

    For each NewArrayExp node, checkTypes must use Ast.updateInits
    on the node to store an array of length 1 that encodes the
    initial value for each of the array's elements.

    For each FieldExp node, checkTypes must use Ast.update1
    on the node to store the offset of the field that is
    referenced by the node.

The instructor is providing Scheme code to parse a quirk20
program and to implement the Qtype abstract data type.
See the documentation on the web page.  The code will be in

    /course/com3355/Assignments/Assignment2

Please do not modify the instructor's code, as that would
make it harder to combine your semantic analysis phase with a
code generator written by someone else.  If you find a bug in
the instructor's code, please report it.

Submit your code using the /course/com3355/submit-3355 script
that is documented on the course web page.