base production refactor

thue/core.py

@@ -0,0 +1,61 @@
+import re
+
+import thue.parser
+
+
+class Context:
+    def __init__(self, string, match=None):
+        self.string = self.match = None
+        self.set(string, match)
+
+    def enter(self):
+        return Context(self.string, self.match)
+
+    def set(self, string, match=None):
+        if match is None:
+            match = re.match(r'^.*$', string)
+        self.string = string
+        self.match = match
+
+    def exit(self, ctx):
+        diff = self.string != ctx.string
+        self.string = ctx.string
+        self.match = ctx.match
+        return diff
+
+    def expand(self, fmt):
+        self.match = thue.parser.ALL_PAT.match(self.string)
+        self.string = self.match.expand(fmt)
+
+    def __str__(self):
+        return f'Ctx[{self.string!r} {self.match[0]!r} {self.match.groups()}]'
+
+
+class Production:
+    fields = ()
+
+    def apply_local(self, local):
+        pass
+
+    def apply(self, ctx):
+        local = ctx.enter()
+        self.apply_local(local)
+        return ctx.exit(local)
+
+    def __str__(self):
+        field_list = ' '.join(map(str, self.fields))
+        return f'{type(self)}[{field_list}]'
+
+
+class Program(Production):
+    def __init__(self, prod):
+        self.prod = prod
+        self.fields = prod,
+
+    def apply_local(self, local):
+        self.prod.apply(local)
+
+    def run(self, init=''):
+        ctx = Context(init)
+        self.prod.apply(ctx)
+        return ctx.string