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from tokens import *
def peek(inp):
if len(inp) == 0:
return None
return inp[0]
def parse_expression(tkns):
# expressions MUST start with a symbol (for now?)
symbol = None
args = []
for idx, t in enumerate(tkns):
#if isinstance(t, NebOpen):
if idx == 0:
if not isinstance(t, NebSymbol):
raise Exception("expressions must start with a symbol")
else:
symbol = t
elif isinstance(t, NebClose):
return NebExpression(symbol, args), tkns[idx + 1:]
else: # TODO nested expressions
args.append(t)
raise Exception("couldn't parse expression!")
def parse(tkns, parsed):
nxt = peek(tkns)
if nxt is None:
return parsed
if isinstance(nxt, NebOpen):
expr, remainder = parse_expression(tkns[1:])
parsed.append(expr)
return parse(remainder, parsed)
elif isinstance(nxt, NebLiteral):
parsed.append(nxt)
return parse(tkns[1:], parsed)
elif isinstance(nxt, NebSymbol):
parsed.append(nxt)
return parse(tkns[1:], parsed)
else:
raise Exception("expecting an expression or a literal")
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