Homework week 3

1) nut-compiler has not been finished. There are no "let", "enum" and string. Extend nut-compiler (nut.txt) to include them. You can have a look at "nut3-compiler.txt" for a guide, or you can look at the C source in "nut31/compile" directory, nut.c.

2) (bonus) n-code object can be made "relocatable", i.e. not dependent on the absolute location in the memory. This can be achieved by "linearising" the n-code tree. The simplest form is the "prefix" form. See the following example:

source
(+ 2 3)

becomes readable n-code:

(+ lit.2 lit.3)

which is stored in the memory (say starts at 6)

2 1 16 3 0
4 1 16 2 2
6 1 6 0 4

this object is not relocatable, it embeds the absolute location in the "next" link. A list can be represented by prefixing it with its length, no "next" link is necessary.

(+ lit.2 lit.3)

becomes

3 + lit.2 lit.3

another example:

(+ lit.2 (+ lit.3 lit.4))

becomes
3 + lit.2 3 + lit.3 lit.4

This representation can be converted into an n-code tree (at any location).

Write a program to output n-code object in linear form to a file and read it back into the memory properly at a different location. You can use "prList" to print the readable n-code out to check it.

22 June 2006