scripts: csv.py: Frac expr tweaks

- Allow single-arg frac:

  - frac(a)    => a/a
  - frac(a, b) => a/b

  This was already supported internally.

- Implicitly cast to frac in frac ops:

  - ratio(3) => ratio(3/3) => 1.0 (100%)
  - total(3) => total(3/3) => 3

  This makes a bit more sense than erroring.

scripts/csv.py

@@ -450,7 +450,10 @@ class RExpr:
             return RFrac
 
         def eval(self, fields={}):
-            return RFrac(self.a.eval(fields), self.b.eval(fields))
+            if len(self) == 1:
+                return RFrac(self.a.eval(fields))
+            else:
+                return RFrac(self.a.eval(fields), self.b.eval(fields))
 
     # fold exprs
     @func('sum')
@@ -596,7 +599,7 @@ class RExpr:
             return RFloat
 
         def eval(self, fields={}):
-            v = self.a.eval(fields)
+            v = RFrac(self.a.eval(fields))
             if not float(v.b):
                 return RFloat(1)
             else:
@@ -608,7 +611,7 @@ class RExpr:
             return RInt
 
         def eval(self, fields={}):
-            return self.a.eval(fields).b
+            return RFrac(self.a.eval(fields)).b
 
     @func('abs')
     class Abs(Expr):