Find the innermost Env where var appears.
(self, var)
| 132 | % (to_string(parms), to_string(args))) |
| 133 | self.update(zip(parms,args)) |
| 134 | def find(self, var): |
| 135 | "Find the innermost Env where var appears." |
| 136 | if var in self: return self |
| 137 | elif self.outer is None: raise LookupError(var) |
| 138 | else: return self.outer.find(var) |
| 139 | |
| 140 | def is_pair(x): return x != [] and isa(x, list) |
| 141 | def cons(x, y): return [x]+y |