boot2

commit cf5f560c7bb3255588cc29a42027e9c9b4bfaa05
parent b186d29846b5a79aecd11a685b1517b3a2360b10
Author: Ryan Sepassi <rsepassi@gmail.com>
Date:   Sat, 25 Apr 2026 06:40:07 -0700

Use %tail / %tailr at every scheme1 tail position

Replace %call+%eret (and the lone %callr in apply) with the frame-popping
%tail / %tailr ops in every position that returns the callee's value
unmodified: eval -> apply / eval_if, eval_if -> eval (both branches),
eval_args -> cons, apply -> prim entry, parse_one -> parse_list /
parse_atom, parse_atom -> intern / parse_int, register_primitives ->
sym_set_global. The eval -> sym_global call stays %call because its
result is checked for UNBOUND before returning. Establishes the
LISP-C.md §11 invariant ahead of `lambda`.

Diffstat:
M
scheme1/scheme1.P1pp
 | 
36
+++++++++++++++---------------------

1 file changed, 15 insertions(+), 21 deletions(-)
diff --git a/scheme1/scheme1.P1pp b/scheme1/scheme1.P1pp
@@ -398,8 +398,7 @@
     %addi(a1, a0, -35)
     %beqz(a1, &::hash)
 
-    %call(&parse_atom)
-    %eret
+    %tail(&parse_atom)
 
     ::lparen
     # Consume '(' and read items until ')'.
@@ -407,8 +406,7 @@
     %ld(t1, t0, 0)
     %addi(t1, t1, 1)
     %st(t1, t0, 0)
-    %call(&parse_list)
-    %eret
+    %tail(&parse_list)
 
     ::rparen
     %die(msg_unexp_rparen, 6)
@@ -563,13 +561,12 @@
     %ld(t1, sp, 8)
     %ld(t2, sp, 0)
     %sub(a1, t1, t2)
-    %call(&intern)
-    %eret
+    %tail(&intern)
 
     ::is_int
     %ld(a0, sp, 0)
     %ld(a1, sp, 8)
-    %call(&parse_int)
+    %tail(&parse_int)
 })
 
 # parse_int(start_off=a0, end_off=a1) -> tagged fixnum in a0. Leaf.
@@ -668,17 +665,16 @@
     %ld(a1, sp, 8)
     %call(&eval_args)
 
-    # apply(fn, args)
+    # apply(fn, args) -- tail call
     %mov(a1, a0)
     %ld(a0, sp, 16)
-    %call(&apply)
-    %eret
+    %tail(&apply)
 
     ::do_if
     %ld(a0, sp, 0)
     %cdr(a0, a0)
     %ld(a1, sp, 8)
-    %call(&eval_if)
+    %tail(&eval_if)
 })
 
 # eval_args(args=a0, env=a1) -> evaluated args list (cons-built).
@@ -702,11 +698,10 @@
     %ld(a1, sp, 8)
     %call(&eval_args)
 
-    # cons(val, rest)
+    # cons(val, rest) -- tail call
     %mov(a1, a0)
     %ld(a0, sp, 16)
-    %call(&cons)
-    %eret
+    %tail(&cons)
 
     ::nil
     %li(a0, %imm_val(%IMM.NIL))
@@ -735,7 +730,7 @@
     ::prim
     %ld(t0, a0, 5)         ; t0 = entry word (offset = -3 + 8)
     %ld(a0, sp, 0)         ; args list -> a0
-    %callr(t0)
+    %tailr(t0)
 })
 
 # =========================================================================
@@ -773,22 +768,21 @@
     %li(t0, %imm_val(%IMM.FALSE))
     %beq(a0, t0, &::else_branch)
 
-    # then-branch: eval(cadr(rest), env)
+    # then-branch: tail-eval(cadr(rest), env)
     %ld(a0, sp, 0)
     %cdr(a0, a0)
     %car(a0, a0)
     %ld(a1, sp, 8)
-    %call(&eval)
-    %eret
+    %tail(&eval)
 
     ::else_branch
-    # else-branch: eval(caddr(rest), env)
+    # else-branch: tail-eval(caddr(rest), env)
     %ld(a0, sp, 0)
     %cdr(a0, a0)
     %cdr(a0, a0)
     %car(a0, a0)
     %ld(a1, sp, 8)
-    %call(&eval)
+    %tail(&eval)
 })
 
 # =========================================================================
@@ -825,7 +819,7 @@
     %call(&intern)
     %untag_sym(a0, a0)          ; idx
     %ld(a1, sp, 0)               ; HEAP-tagged prim ptr
-    %call(&sym_set_global)
+    %tail(&sym_set_global)
 })
 
 # prim_sys_exit_entry(args=a0). Args is a one-element list whose car is