sicp-ex-5.31

  
  
  
 (f 'x 'y)     => all the saves and restores are superfluous. because they doesn't change the registers. 
 ((f) 'x 'y)   => all the saves and restores are superfluous. 
 (f (g 'x) y) => register proc, argl will needed save and restore. 
 (f (g 'x) 'y) => same to the above one. 

  
  
  
 (f 'x 'y)  => all the saves are not necessary. 
 ((f) 'x 'y) => not necessary too, although (f) is a compound-procedure, it will change the env register to the status where f is defined, but it will not affect the quoted 'x and 'y. 
 (f (g 'x) y) => proc and argl are necessary, save env before eval (g 'x) is necessary too, it will change the env register and y will be affected. 
 (f (g 'x) 'y) => proc and argl is necessary, but no need to save env before eval (g 'x) cause 'y is quoted, it will not fetch any value in the env, and env register will be reset to the status where f is defined 
  

I think this matches Perry's answer

┌──────────────────┬───────────┬───────────┬───────────┬───────────┐
│                  │ operator  │ operands  │ operands  │ op'd seq  │
│                  │ env       │ env       │ argl      │ proc      │
├──────────────────┼───────────┼───────────┼───────────┼───────────┤
│ 1: (f 'x 'y)     │ eliminate │ eliminate │ eliminate │ eliminate │
├──────────────────┼───────────┼───────────┼───────────┼───────────┤
│ 2: ((f) 'x 'y)   │ eliminate │ eliminate │ eliminate │ eliminate │
├──────────────────┼───────────┼───────────┼───────────┼───────────┤
│ 3: (f (g 'x) y)  │ eliminate │           │           │           │
├──────────────────┼───────────┼───────────┼───────────┼───────────┤
│ 4: (f (g 'x) 'y) │ eliminate │ eliminate │           │           │
└──────────────────┴───────────┴───────────┴───────────┴───────────┘


Operator Env
============

Only need to save/restore if env could change in evaluating the operator and
we need env to evaluate the operands.  In the case of 2: the environment
would be changed in evaluating (f) but the environment is not needed to
evaluate symbols 'x and 'y.


Operands Env
============

Only need to save/restore between operands if there's an operand expression
that might change env and a subsequent operand that needs env for variable
lookup.  This is only the case for 3:.


Operands Argl
=============

We need to save/restore argl anytime there's an operand that might change
the value of argl.  That's 3: and 4:.


Operaand Sequence Proc
======================

We need to save/restore proc if there's any operand that might change the
value of proc.  That's 3: and 4:.