Assignment 4

Function calls are all well and good, but we will find that the stack, like the heap, can also run out of space.

Worse, we will find that some of our (well-formed!) Scheme programs exhibit crashes with our compiler that do not occur under a Big Professional Compiler like Guile.

Consider: we have no looping constructs. How does one “loop” over a string by index (for example)? With a recursive function. And what if the number of characters in the string is greater than the number of stack frames available? Hmmm.

This is why the Scheme standards guarantee that certain kinds of calls do not use stack space: tail calls.

Recognizing tail calls

Tail calls

• A tailcall form and TAILCALL opcode

Optionally, faster tail calls

Build some library functions

• map
• fold
  • foldl vs foldr

Complex constants

• constant-init
• constant-ref
• labels form must handle begin-like behavior

Question: why not just bake constant data into the .data section (or equivalent)?

Submitting your homework