I agree, and although NimbleParsec has replaced a little bit of my ExSpirit library usages, but I still use ExSpirit on occasion just because NimbleParsec can’t handle some things as well (especially around state information).
The issues in your post are for NimbleParsec supposed to be done by a secondary pass, it’s not a single-pass parsing library (which loses a lot of it’s capabilities).
I’m sure Jose would be up for accepting PR’s to integrate the features that my ExSpirit library has, the state handling capabilities would be a HUGE boon for me and I could drop ExSpirit if it’s features were ported over. 
For note, that same example in ExSpirit (give or take, should actually be parsing out whatever comes after if/while):
iex(1)> defmodule Testing do
...(1)> use ExSpirit.Parser, text: true
...(1)>
...(1)> defrule identifier(tag(:id, chars([?a..?z, ?A..?Z, ?0..?9], 1)))
...(1)>
...(1)> defrule keywords(context) do
...(1)> symbols_ =
...(1)> ExSpirit.TreeMap.new()
...(1)> |> ExSpirit.TreeMap.add_text("if", :if) # Value can be a function to return a parser
...(1)> |> ExSpirit.TreeMap.add_text("while", :while) # Value can be a function to return a parser
...(1)> context |> symbols(symbols_) |> lookahead_not(identifier()) # Should actually parse the if/while instead...
...(1)> end
...(1)>
...(1)> defrule expr(alt([
...(1)> keywords(),
...(1)> identifier(),
...(1)> ]))
...(1)> end
{:module, Testing,
<<70, 79, 82, 49, 0, 0, 127, 188, 66, 69, 65, 77, 65, 116, 85, 56, 0, 0, 3, 7,
0, 0, 0, 84, 14, 69, 108, 105, 120, 105, 114, 46, 84, 101, 115, 116, 105,
110, 103, 8, 95, 95, 105, 110, 102, 111, 95, ...>>, {:expr, 1}}
iex(2)> import ExSpirit.Parser
ExSpirit.Parser
iex(3)> parse("if", Testing.identifier)
%ExSpirit.Parser.Context{
column: 3,
error: nil,
filename: "<unknown>",
line: 1,
position: 2,
rest: "",
result: {:id, "if"},
rulestack: [],
skipper: nil,
state: %{},
userdata: nil
}
iex(4)> parse("if", Testing.identifier).result
{:id, "if"}
iex(5)> parse("iffy", Testing.identifier).result
{:id, "iffy"}
iex(6)> parse("if", Testing.expr).result
:if
iex(7)> parse("iffy", Testing.expr).result
{:id, "iffy"}
I should probably just finish my ExSpirit.Parserx rewrite (which started just before NimbleParsec came out) as it is faster.
