stash old vm

moving on to getting mom to work and can’t have both
interpreter and elf broke, about 100 tests  went

stash/vm/method_compiler/while_statement.rb

@@ -0,0 +1,42 @@
+module Vm
+  module WhileStatement
+
+    def on_WhileStatement statement
+      #branch_type , condition , statements = *statement
+
+      condition_label = compile_while_preamble( statement )  #jump there
+
+      start = compile_while_body( statement )
+
+      # This is where the loop starts, though in subsequent iterations it's in the middle
+      add_code condition_label
+
+      compile_while_condition( statement )
+
+      branch_class = Object.const_get "Risc::Is#{statement.branch_type.capitalize}"
+      # this is where the while ends and both branches meet
+      add_code branch_class.new( statement.condition , start )
+
+      nil # statements don't return anything
+    end
+    private
+
+    def compile_while_preamble( statement )
+      condition_label = Risc.label(statement.condition , "condition_label")
+      # unconditionally branch to the condition upon entering the loop
+      add_code Risc::Branch.new(statement.condition , condition_label)
+      condition_label
+    end
+    def compile_while_body( statement )
+      start = Risc.label(statement , "while_start" )
+      add_code start
+      reset_regs
+      process(statement.statements)
+      start
+    end
+    def compile_while_condition( statement )
+      reset_regs
+      process(statement.condition)
+    end
+  end
+end