On Sunday, February 5, 2017 at 4:06:13 AM UTC+5:30, Matthew Butterick wrote:
> On Feb 4, 2017, at 8:18 AM, Sourav Datta <soura...@gmail.com> wrote:
>
> (require/typed "grammar1.rkt"
> [parse (->* (Listof Token)
> (Any)
> Syntax)])
>
> Type Checker: Type (->* (Listof Token) (Any) Syntax) could not be converted
> to a contract: required a flat contract but generated a chaperone contract
> in: (->* (Listof Token) (Any) Syntax)
>
> I am not sure what this means exactly but is this because Racket does not see
> the automatically exported function parse (or parse-tree) from a #lang brag
> module? And, is there a way to correct this error so that I can call the
> parse function from a TR module?
>
>
> 1) That type declaration for `parse` seems both too strict (in terms of the
> input `parse` will accept), and not quite accurate in terms of order of
> arguments. I might do it this way:
>
>
>
> (require/typed brag/support
> [#:opaque Token token-struct?]
> [token (->* ((U String Symbol))
> (Any
> #:line Positive-Integer
> #:column Natural
> #:position Positive-Integer
> #:span Natural
> #:skip? Boolean)
> Token)])
>
>
> (define-type Tok (U String Symbol Token Void))
>
>
> (require/typed "grammar1.rkt"
> [parse (case-> ((U (Listof Tok) (-> Tok)) . -> . Any)
> (Any (U (Listof Tok) (-> Tok)) . -> . Any))])
>
>
>
>
> 2) If I use `Any` rather than `Syntax` as the output type, then `parse`
> works.
Thanks! That worked. Yes the type signatures were wrong for parse and I
realized that after re-reading the documentation. Also, I found that instead of
returning `Any` we could also return `(Syntaxof Any)` like this:
(define-type Input-Token (U String Symbol Token Void 'EOF))
(define-type Token-Source (U (-> Input-Token)
(Listof Input-Token)))
(require/typed "grammar1.rkt"
[parse (case-> (-> Token-Source (Syntaxof Any))
(-> Any Token-Source (Syntaxof Any)))])
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