2432 - first stab at making ingredients immutable

The rule is, an address ingredient is only modifiable if:
  a) it's also a product
  b) it's /contained-in some other ingredient+product

Only if an ingredient is a modifiable can you:
  a) call get-address or index-address on it (the only way to write to it)
  b) call other recipes that also return it in a product

I still don't check copies of the address. That's next.

Core mu passes this check, but none of the example apps do. edit/ and
sandbox/ are known to fail.

1 files changed, 2 insertions, 0 deletions

diff --git a/021check_instruction.cc b/021check_instruction.cc
index 1d831369..5e258b9b 100644
--- a/021check_instruction.cc
+++ b/021check_instruction.cc
@@ -73,6 +73,8 @@ recipe main [
 +error: main: can't copy 34 to 1:address:number; types don't match
 
 :(code)
+// copy arguments because later layers will want to make changes to them
+// without perturbing the caller
 bool types_match(reagent lhs, reagent rhs) {
   // '_' never raises type error
   if (is_dummy(lhs)) return true;