Flex for VS Code

Flex is an open, typed specification language for software architecture. A specification names the components of a system, the messages they exchange, and the protocols that put those exchanges in order. It is precise enough to be checked formally, and structured so that changing it tells you what else has to change.

This extension adds Flex to VS Code: highlighting, diagnostics as you type, project-wide navigation, and completion.

The language in brief

Start with the data and the parts that exchange it.

module hvac.control

message struct SetPoint { celsius: float32; }
message struct Ack {}
message struct Fault { code: uint16; }

component Thermostat;
component Furnace;

connection Control from Thermostat to Furnace;

A protocol says what happens, and in what order. Here the thermostat sends a set point, and the furnace answers with either an acknowledgement or a fault.

global protocol Adjust {
  exch any SetPoint into let target: SetPoint from Thermostat to Furnace on Control;

  choice in Furnace
  | true => exch any Ack from Furnace to Thermostat;
  | else => exch any Fault from Furnace to Thermostat;
  end
}

exch is one exchange between two components. into let binds the message, so later steps can refer to its fields. choice in Furnace records which component decides the branch — worth stating explicitly, because everyone else has to be able to tell the branches apart. Protocols can also run branches concurrently with parallel, loop, and be written from a single component's point of view as a local protocol built from send and recv.

The payoff arrives when the design changes. Add a field to Fault, rename SetPoint, or move Control to a different pair of components, and the places that no longer fit show up as diagnostics instead of as a search through the tree.

In the editor

• Errors and warnings on open and as you type, over every .flex file in the workspace rather than just the open buffer.
• Go to definition, find all references, and rename, each of them project-wide and following import across files.
• Hover for the inferred type and the reconstructed declaration at the cursor.
• Completion of the names that are in scope where you are typing.
• Outline and breadcrumbs for a file; symbol search across the workspace.
• A TextMate grammar for immediate coloring, with semantic highlighting from the server layered over it once analysis completes.
• Module paths in import rendered as links, so they are Ctrl- or Cmd-clickable.

Getting started

Install the extension, then open a folder that contains .flex files. The language server is bundled in the extension, so there is no separate download and no toolchain to set up.

Analysis covers the whole workspace, not one file at a time, so imports and cross-file references resolve from the first keystroke. Everything runs on your machine.

Leaving files out

Every .flex file under a workspace root belongs to the project by default. If a tree also holds build output or fixtures you would rather not see in the problems list, put a .flexignore at the workspace root:

target/            # a directory of this name, at any depth
generated/*.flex   # a glob inside one path segment
/vendor/           # a leading slash anchors the pattern to the root

A pattern ending in / matches directories only; one without a slash matches a basename at any depth; one containing a slash is anchored to the root. With no .flexignore, nothing is excluded.

Settings

The output channel also reports which server binary was chosen, which is the first thing to check if the extension seems inactive.

License and notices

Use of this extension is governed by the FlexLang Visual Studio Code Extension Free License Agreement, included in the package as LICENSE.txt. Attribution for the open source components the extension bundles is in THIRD-PARTY-NOTICES.txt.

More

Language documentation and reference: https://flexlang.org/

Questions, bug reports, and security reports: support@tangramflex.com