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from tokens import *
def peek(inp):
if len(inp) == 0:
return None
return inp[0]
def parse_expression(tkns):
symbol = None
args = []
add_idx = 0
for idx, t in enumerate(tkns):
# if we evaluated a nested expression, skip ahead
# TODO or list?
if add_idx > 0:
add_idx -= 1
continue
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:], idx + 1
# nested expressions
elif isinstance(t, NebOpen):
expr, remainder, add_idx = parse_expression(tkns[idx + 1:])
args.append(expr)
elif isinstance(t, NebListStart):
# TODO this might need to be add_idx + (return of parse_list)
lst, remainder, add_idx = parse_list(tkns[idx + 1:])
args.append(lst)
else:
args.append(t)
raise Exception("couldn't parse expression!")
def parse_list(tkns):
items = []
add_idx = 0
for idx, t in enumerate(tkns):
if add_idx > 0:
add_idx -= 1
continue
if isinstance(t, NebListEnd):
return NebList(items), tkns[idx + 1:], idx + 1
elif isinstance(t, NebOpen):
expr, remainder, add_idx = parse_expression(tkns[1 + idx:])
items.append(expr)
elif isinstance(t, NebLiteral):
items.append(t)
elif isinstance(t, NebSymbol):
items.append(t)
elif isinstance(t, NebListStart):
# TODO: this probably means lists of lists don't work
lst, remainder, add_idx = parse_list(tkns[1:])
items.append(lst)
raise Exception("couldn't parse list!")
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, NebListStart):
lst, remainder, _ = parse_list(tkns[1:])
parsed.append(lst)
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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