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[docs] extend explanation of current-type-eval

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Stephen Chang 2016-10-04 14:46:34 -04:00
parent 7c68789628
commit 0e0d4ce192
1 changed files with 13 additions and 8 deletions
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turnstile/scribblings/reference.scrbl
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@ -242,17 +242,22 @@ Reuses @racket[name]s from @racket[base-lang].}
@section{Lower-level Functions}
This section describes lower-level functions. It's usually not necessary to call these directly,
since @racket[define-typed-syntax] and other forms already do so.
This section describes lower-level functions and parameters. It's usually not
necessary to call these directly, since @racket[define-typed-syntax] and other
forms already do so, but some type systems may require extending some
functionality.
@defparam[current-type-eval type-eval type-eval]{
A phase 1 parameter for controlling "type evaluation". A @racket[type-eval] function consumes and
produces syntax.
A phase 1 parameter for controlling "type evaluation". A @racket[type-eval]
function consumes and produces syntax. It is typically used to convert a type
into a canonical representation. The @racket[(current-type-eval)] is called
immediately before attacing a type to a syntax object, i.e., by
@racket[assign-type].
It defaults to full expansion, i.e., @racket[(lambda (stx) (local-expand stx 'expression null))];
the default also stores extra surface syntax information used for error reporting.
This is called before a type is attached to a syntax object,
i.e., by @racket[assign-type].}
It defaults to full expansion, i.e., @racket[(lambda (stx) (local-expand stx 'expression null))], and also stores extra surface syntax information used for error reporting.
One should extend @racket[current-type-eval] if canonicalization of types
depends on combinations of different types, e.g., type lambdas and type application in F-omega. }
@defparam[current-typecheck-relation type-pred type-pred]{
A phase 1 parameter for controlling type checking. A @racket[type-pred] function consumes