Tags: Orbion-J/links
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Release 0.9.6
CHANGES:
This release extends the core features of Links and resolves various
minor bugs.
* Links now supports System F-style explicit type abstractions:
For instance, writing `/\ [a, e::Row] { foo }` abstracts the expression `foo`
over type variable `a` and row variable `e`. Here, `foo` must have a unique
type and must be pure (to satisfy the value restriction).
* Fixed a bug in "mixing" query normalisation, which prevented certain queries using
concatenation inside `for` statements from being correctly converted to SQL.
* Links now has basic support for temporal database operations. More information
can be found on the [Wiki](https://github.com/links-lang/links/wiki/Temporal-Databases).
There are new keywords: `valid`, `to`, `vt_insert`, `tt_insert`, and `TemporalTable`.
* A new commandline option `--compile` (shorthand `-c`) has been
added, which runs Links in a "compile only" mode. In this mode the
JavaScript compilation artefact can be saved to a file (the naming
of this file is controlled via the commandline option `-o`). Note
that the generated file may not be directly runnable without linking
the runtime system first. Currently, the runtime system must be
linked manually.
* Fixed a bug where calling either of `newAP`, `newClientAP`, and
`newServerAP` on the client-side would crash the client.
* It is now possible to dispatch an MVU message from outside of the
event loop. This is particularly useful, for example, when dealing
with a persistent, stateful thread which is receiving messages from
a server. New things include:
+ A new type alias `MvuHandle(msg)`.
+ A family of runners: `runHandle`, `runCmdHandle`,
`runSimpleHandle` which return an `MvuHandle(msg)` rather than the
unit value.
+ A new dispatcher `Mvu.dispatch : (msg, MvuHandle(msg)) ~> ()`,
which directly dispatches a message to the MVU loop.
* The built-in webserver now supports SSL connections. To enable
secure connections, you must first obtain an adequate certificate
and key, e.g. via Let's Encrypt or a self-signed certificate. The
latter can be useful for testing, e.g. the following command starts
an interactive process to create a self-signed certificate (that
uses 4096 bits RSA encryption and is valid for 365 days):
```shell
openssl req -x509 -newkey rsa:4096 -keyout server.key -out server.crt -days 365 -nodes
```
After obtaining a valid certificate, you must tell Links to run in SSL
m
8000
ode and you must also tell it how to locate the `key` and `crt`
file. This can be done via a configuration file, e.g.
```
Release 0.9.5 CHANGES: This is a minor hotfix release. * The database query deduplication now correctly handles subexpressions recursively. * The mixing normaliser for database queries now correctly split comprehensions along concatenation * Fixed a bug whereby messages received on the client-side would not be deserialised correctly. * The Links runtime, now internally, uses `Lwt.pause` rather than the deprecated `Lwt_main.yield`. As a side effect we have updated the Lwt version constraint to be greater or equal to `5.0.0`.
Release 0.9.4
CHANGES:
Links now provides experimental support for SQL queries mixing set and bag semantics.
When the `mixing_norm=on` flag is added to the configuration file, or when a query is defined in a `query mixing { ... }` block, Links will use a new query evaluator, allowing the programmer to call deduplication functions (`dedup` and `distinct`) within database queries. These are handled with set-based SQL statements `select distinct / union`, in addition to the usual bag-based `select / union all`.
# will run on the DB as "select distinct e.dept as dept from employees"
query mixing {
dedup(for (e <-- employees) [(dept = e.dept)])
}
Queries mixing set and bag semantics may, in some cases, require the use of the SQL:1999 keyword `lateral`; Links implements an optional query transformation to produce queries that do not use `lateral` (allowing the use of older DBMSs): this behaviour is enabled by using `query delat` in place of `query mixing`.
Further information on this feature is provided in the [Links GitHub wiki](https://github.com/links-lang/links/wiki/Deduplication-in-database-queries).
Links now includes a primitive type, `DateTime`, for dates and times.
This is a *breaking change* from previous versions, where `dateToInt`
and `intToDate` operated on a record.
The primitive type allows us to better timezones, and also allows us
to work seamlessly with timestamps in the database.
Obtain a DateTime via:
* the `now()` function to get a timestamp for the current local time
* Using `parseDate` on an ISO-formatted string (e.g., `parseDate("26-07-2021 14:26:00+1")`)
* A `DateTime` field in the database
* `intToDate(X)` where `X` is a UNIX timestamp
* `beginningOfTime` and `forever`, which are special timestamps guaranteed to be less than (resp. greater than) all other timestamps
Project fields out of the type:
* utcYear, utcMonth, utcDay, utcHours, utcMinutes, utcSeconds, utcMilliseconds projects the given field in the UTC time zone
* localYear, localMonth, localDay, localHours, localMinutes, localSeconds, localMilliseconds projects the given field in the local time zone
* dateYear, dateMonth, dateDay, dateHours, dateMinutes, dateSeconds, dateMilliseconds projects the given field in a given timezone (e.g., to project the hours field of a DateTime dt in BST, one would write `dateHours(dt, 1)`, where 1 is the timezone offset.
You can also print out the `DateTime` using `show` (which is an alias of
`showLocal`) and `showUTC`.
`DateTime`s are comparable as normal.
Due to limitations of the underlying library, the minimum timezone granularity is one hour. Unfortunately, this means we can't handle Indian timezones, for example.
**Breaking change**: New syntax has been added to support type arguments of kind `Presence`. Here are some example of the syntax:
```links
typename T(p::Presence) = (foo{p});
(foo=4200) : T({:Int}) # Present with type Int
() : T({-}) # Absent
(foo=4200) : T({%}) # Unnamed flexible variable
(foo=true) : T({%p}) # Named flexible variable
fun(r : T({_})) { () } # Anonymous presence variable
fun(r : T({p})) { r : T({p}) } # Named presence variable
```
The syntactic sugar for effect and record fields which lets one omit the `()` has been removed in order to resolve the otherwise ambiguity between the presence type argument `{wild}` from the row type argument `{wild}`. Note however that it is still possible to omit the `()` for variant fields.
It is now possible to annotate type variables with `Mono` restriction, e.g. `sig id : (a::(Any,Mono)) -> a::(Any,Mono)`.
* Effect variables can be recursive, e.g. `{ |(mu a.F:(() { |a}-> ()) {}-> b|c)}`.
* **Breaking change**: Recursive rows are no longer restricted to variant syntax, i.e. separating fields using `|`. Recursive record and effects rows separate fields using `,` now.
* Recursive variants with no directly exposed fields no longer require the vertical bar separating fields from the row variable, e.g. `[|(mu a. Foo)|]` is equivalent to `[| |(mu a . Foo)|]`.
This version of Links introduces a new pretty printer for types, called Roundtrip. This fixes various round-tripping issues.
The Roundtrip printer is now active by default. The old printer is still present.
The printer(s) to be used can be selected using the setting `types_pretty_printer_engine`, with the following values:
* `roundtrip`: the new printer
* `old`: the original printer
* `derived`: no pretty printing - prints the OCaml representation of the types
Note that one can select multiple printers at once, for comparison; this is done by separating printer names by commas, e.g.:
```links
@set types_pretty_printer_engine "roundtrip,old";
```
This version implements enhanced syntactic sugar for effects. The changes influence both the Roundtrip printer (see above) and the desugaring passes (between parsing and typechecking).
(*Note: Most of effect sugar, and in particular the changes introduced in this version, requires the `effect_sugar` setting to be `true`.*)
There is a new setting `effect_sugar_policy` which allows one to set which components of effect sugar to use. The available options (with shortcuts for convencience) are:
* `presence_omit` [shotcut `pres`]: omit presence polymorphic operations within effect rows
* `alias_omit` [shortcut `alias`]: hide empty (and emptied using `pres`) shared effect rows in the last argument of aliases
* `arrows_show_implicit_effect_variable` [shortcut `show_implicit`]: display the imlicit shared effect on arrows
* `arrows_curried_hide_fresh` [shortcut `chf`]: in curried functions, argument collection arrows are assumed to have fresh effects and these are hidden
* `contract_operation_arrows` [shortcut `contract`]: contract operation arrows: `E:() {}-> a` to `E:a` and `E:(a) {}-> b` to `E:(a) -> b`
* `open_default` [shortcut `open`]: effect rows are open by default, closed with syntax `{ | .}`
* `final_arrow_shares_with_alias` [shortcut `final_arrow`]: final arrow and a following type alias may share implicit effects
* `all_implicit_arrows_share` [shortcut `all_arrows`]: all arrows with implicit effect vars will be unified, an experimental setting
Multiple of these can be selected, separated by commas, e.g.:
```links
@set effect_sugar_policy "pres,alias,contract";
```
A version of the above is also available by entering `@help effect_sugar_policy;` in Links.
These changes are explained in more depth and with examples in [Links GitHub Wiki/Effect Sugar](https://github.com/links-lang/links/wiki/Effect-Sugar).
* Relational lenses are now enabled by default.
* Fixed a bug where the REPL would unconditionally print a stacktrace for unknown directives.
* Fixed a bug where deeply nested JSON literals would cause the client to stack overflow.
* Fixed a bug where big server side values would cause the client to stack overflow.
* Fixed JavaScript compilation of top-level anonymous functions.
* Fixed a bug where the server would inadvertently respond with response `500` following the (successful) termination of a server side process.
* The body of an escape expression has been made more permissive (grammatically) as it can now be any expression.
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