class MacroExec(object):
'''A MacroExec object constructs a local symbol table (LST) every time
the macro is called.
When a macro is called, it builds a LST. If a symbol is
referenced that isn't contained in the LST then the macro looks to
the global symbol table (GST). The macro can reference values
from the GST, but it can not bind new values to the GST. Macros
bind values only to LST, so a method is used for all binding that
takes care to obey this invarient.
'''
def __init__(self, name, args, body):
self.name = name
self.args = args
self.body = body
self.lst = SymbolTable()
def num_args(self):
return len(self.args)
def bind(self, exprList):
'''bind arguments to the local symbol table'''
assert len(exprList) == len(self.args)
bindPairs = zip(self.args, [e.eval() for e in exprList])
# this mutates self.lst making for sad things to happen next
# time this macro is invoked. or maybe not, maybe it simply
# clobbers the old bindings?
self.lst = SymbolTable()
self.lst.bind(bindPairs)
def generate(self, symtab):
''' generate a sequence of bytes '''
# copy the macro body so the Ident nodes are preserved for the
# next invocation of this macro.
# import copy
# ast = copy.deepcopy(self.body)
ast = self.body
ast.replace_idents(self.lst)
ast.replace_idents(symtab)
return ast.generate(symtab)
