Thanks all @PMunch , choltreppe, and @nrk!
@nrk I'd seen those docs, but I couldn't see why even the proc parameters would
be gensym'd. Is there a way to actually see the expanded Nim code. Like your
comment:
# works, as it expands to something like:
# let x`gensym0 = "hello world"
# echo x`gensym0
# let x`gensym1 = "dlrow olleh"
# echo x`gensym1
Run
could I actually see that without getting headed off by compiler errors? Kind
of like how `dumpAst` works but without having to do it in the macro (which now
somehow seem clearer than templates to me).
Thanks to all the help here I was able to apply some of this very simply to a
toy parsing project with `{.inject.}` (which I have asked other question for in
the forum)!
template step*(input: untyped): untyped =
(`input`).parse_partial(stream, index)
template generate(body: untyped): untyped =
block:
proc temp[T, R](stream{.inject.}: Stream[T], index{.inject.}: var int):
Result[R] =
`body`
Parser(fn: temp, description: "")
let t: Parser[char, string] = generate:
let x = step test_string("he")
discard step "ll"
let s = step "o"
return x&s
echo t.parse("hello")
Run
Any idea why with the templates, I get this message about mismatched types:
type mismatch: got 'Parser' for 'block:
proc temp[T; R](stream: Stream[T]; index: var int): Result[R] =
let x =
(test_string("he")).parse_partial(stream, index)
discard
("ll").parse_partial(stream, index)
let s =
("o").parse_partial(stream, index)
return x & s
Parser(fn: temp, description: "")' but expected 'Parser[system.char,
system.string]'
Run
I don't see any ambiguity in the typings with `let t: Parser[char, string]`.
Without the type on `t` I get other errors about ambiguity not mis-match. I
also tried just adding types to the template with
`template generate(T, R: typedesc; body: untyped)` and `template generate(T, R:
untyped; body: untyped)`
which brought other problems where the errors suggested (in the first case)
that the types were bound to the `temp` proc in some way (like type mismatch
got `temp.char` expected `system.char`...)
