import results, strutils
type Parser = object
tokens: seq[string]
index: int = 0
proc head(parser: Parser): Result[string, string] =
if parser.index >= parser.tokens.len:
return err("reached eof")
return ok(parser.tokens[parser.index])
proc move(parser: var Parser): Result[Parser, string] =
if parser.index >= parser.tokens.len:
return err("reached eof")
parser.index += 1
return ok(parser)
type
ParserSpecKind = enum
PSK_TERMINAL
PSK_RULE
ParserSpec[T] = object
case kind: ParserSpecKind
of ParserSpecKind.PSK_TERMINAL:
token: string
of ParserSpecKind.PSK_RULE:
rule: proc(parser: var Parser): Result[T, string]
DataType = object
name: string
is_ref: bool
proc parse[T](parser: var Parser, parser_spec: ParserSpec[T]): Result[T, string] =
case parser_spec.kind:
of ParserSpecKind.PSK_TERMINAL:
return ok("terminal")
of ParserSpecKind.PSK_RULE:
return parser_spec.rule(parser)
proc datatype_spec(parser: var Parser): Result[DataType, string] =
let name = ? parser.head()
parser = ? parser.move()
let asterisk = ? parser.head()
var datatype = DataType(name: name, is_ref: asterisk == "*")
return ok(datatype)
const datatype_parser_spec = ParserSpec[DataType](kind: ParserSpecKind.PSK_RULE, rule: datatype_spec)
proc parse(): Result[void, string] =
var tokens: seq[string] = @["int", "*"]
var parser: Parser = Parser(tokens: tokens)
echo parser.parse(datatype_parser_spec)
return ok()
when isMainModule:
echo parse()
I could not find any simpler way to reproduce this error. If you need any further explanation let me know. Running this code snippet using nim r test.nim results into the following error, which I should not arise based on my understanding of control flow. Please help me understand the error.
Hint: used config file '/Users/developer/.choosenim/toolchains/nim-2.2.2/config/nim.cfg' [Conf]
Hint: used config file '/Users/developer/.choosenim/toolchains/nim-2.2.2/config/config.nims' [Conf]
........................................................................................
/Users/developer/parser/src/test.nim(52, 14) template/generic instantiation of `parse` from here
/Users/developer/parser/src/test.nim(35, 14) template/generic instantiation of `ok` from here
/Users/developer/.nimble/pkgs2/results-0.5.1-a9c011f74bc9ed5c91103917b9f382b12e82a9e7/results.nim(454, 41) Error: type mismatch: got 'string' for '"terminal"' but expected 'DataType = object'But this time, I am more concerned about this particular error in the code snippet.
There is nothing to be concerned about, it's so convoluted that you don't understand your own type errors. ;-) Just throw it away and do parsing like it was done before academics screwed it up.