Add more utility functions

1 files changed, 51 insertions, 5 deletions

diff --git a/src/interp/g-util.boot b/src/interp/g-util.boot
index 18af0463..7a93d95a 100644
--- a/src/interp/g-util.boot
+++ b/src/interp/g-util.boot
@@ -46,6 +46,51 @@ module g_-util where
   expandToVMForm: %Thing -> %Thing
 
 
+--% VM forms
+
+++ Make the assumption named `prop' for all symbols
+++ on the lis `syms'.
+assumeProperty(syms,prop) ==
+  for s in syms repeat
+    property(s,prop) := true
+
+assumeProperty('(%and %or),'%nary)
+
+++ We are about to construct a middle end expression
+++ with operator `op, and aguments `form'.  Try to
+++ simplify the structure of the expression.
+flattenVMForm(form,op) == main where
+  main() ==
+    atom form => form
+    EQ(form.op,op) => [op,:flatten(form.args,op,nil)]
+    [flattenVMForm(form.op,op),:flattenVMForm(form.args,op)]
+  flatten(forms,op,acc) ==
+    forms = nil => accu
+    x := flattenVMForm(first forms,op)
+    cons? x and EQ(x.op,op) => flatten(rest forms,op,[:accu,:x.args])
+    flatten(rest forms,op,[:accu,x])
+
+++ Build a midde end expression with given operator and arguments.    
+mkVMForm(op,args) ==
+  if op has %nary then
+    args := flattenVMForm(args,op)
+  op = '%or =>
+    args := REMOVE('%false,args)
+    args = nil => '%false
+    args is [arg] => arg
+    [op,:args]
+  op = '%and =>
+    args := REMOVE('%true,args)
+    args = nil => '%true
+    args is [arg] => arg
+    [op,:args]
+  op = '%not =>
+    [arg] := args
+    arg = '%false => '%true
+    arg = '%true => '%false
+    arg is ['%not,arg'] => arg'
+    ['%not,:args]
+
 --%
 --% Opcode expansion to VM codes.
 --%
@@ -568,13 +613,14 @@ getTypeOfSyntax t ==
 bool: %Thing -> %Boolean
 bool x ==
     null null x
- 
+
+++ Return true is the form `x' is a predicate known to always
+++ evaluate to true.
 TruthP x ==
-    --True if x is a predicate that's always true
-  x is nil => nil
-  x=true => true
+  x = nil or x = '%false => false
+  x = true or x = '%true => true
   x is ['QUOTE,:.] => true
-  nil
+  false
 
 --% Record and Union utils.