HAL/S Language Support for Visual Studio Code

Language Server Protocol (LSP) implementation for HAL/S (High-order Assembly Language/Shuttle), the real-time aerospace programming language that powered NASA's Space Shuttle flight software.

About HAL/S

HAL/S was developed by Intermetrics in the early 1970s under contract to NASA. It was specifically designed for programming onboard computers in real-time aerospace applications. The language powered approximately 85% of the Space Shuttle's Primary Avionics Software System (PASS).

HAL/S was used in:

• Space Shuttle Primary Avionics Software System (PASS)
• Space Shuttle Backup Flight Software (BFS)
• Space Station Freedom (precursor to ISS) software development
• Various NASA spacecraft guidance and control systems

The language is notable for its support of:

• Native vector and matrix operations
• Real-time scheduling primitives
• Multi-line mathematical notation format

Features

• Syntax highlighting for HAL/S constructs
• Code completion for keywords, variables, procedures, functions
• Hover information with type details
• Go to definition for symbols
• Find references across the document
• Document outline showing programme structure
• Support for all HAL/S constructs:
  • Program units (PROGRAM, PROCEDURE, FUNCTION, TASK, COMPOOL)
  • Data types (INTEGER, SCALAR, VECTOR, MATRIX, BOOLEAN, CHARACTER, BIT, EVENT)
  • Real-time primitives (SCHEDULE, WAIT, SIGNAL, PRIORITY, TERMINATE)
  • Array and structure declarations
  • REPLACE macro definitions

Installation

1. Install the extension from the VS Code Marketplace
2. Ensure Python 3.8+ is installed and available in PATH
3. Open any .hal or .hals file

File Extensions

Extension	Description
.hal	HAL/S source file
.hals	HAL/S source file (alternate)

Language Overview

HAL/S uses an ALGOL-like syntax with uppercase keywords:

C HAL/S NAVIGATION EXAMPLE
C FOR SPACE SHUTTLE FLIGHT SOFTWARE

SHUTTLE_NAV: PROGRAM;
    /* Declare constants */
    DECLARE PI CONSTANT(3.14159265);
    DECLARE G CONSTANT(9.80665);

    /* Declare variables */
    DECLARE ALTITUDE SCALAR;
    DECLARE VELOCITY VECTOR(3);
    DECLARE POSITION VECTOR(3);
    DECLARE ATTITUDE MATRIX(3,3);
    DECLARE ENGINE_ON BOOLEAN;
    DECLARE ABORT_FLAG EVENT;

    /* Arrays */
    DECLARE SENSOR_DATA ARRAY(10) SCALAR;

    /* Navigation loop */
NAV_LOOP:
    DO WHILE ENGINE_ON;
        /* Update position */
        POSITION = POSITION + VELOCITY * 0.1;

        /* Check altitude */
        IF ALTITUDE < 100.0 THEN
            SIGNAL ABORT_FLAG;

        GO TO NAV_LOOP;
    END;

CLOSE SHUTTLE_NAV;

/* Guidance function */
COMPUTE_THRUST: SCALAR FUNCTION(MASS, ACCEL);
    DECLARE MASS SCALAR;
    DECLARE ACCEL VECTOR(3);
    DECLARE THRUST SCALAR;

    THRUST = MASS * ABVAL(ACCEL);
    RETURN THRUST;
CLOSE COMPUTE_THRUST;

/* Real-time task */
NAV_TASK: TASK;
    DECLARE STATE VECTOR(6);

    DO WHILE TRUE;
        WAIT FOR 0.1 SECONDS;
        /* Update navigation state */
        STATE = STATE;
    END;
CLOSE NAV_TASK;

Key Syntax Elements

• Comments: C in column 1, or /* ... */
• Multi-line format: E (exponent), S (subscript), M (main) line prefixes
• Assignment: =
• Program units: label: PROGRAM;, label: PROCEDURE;, etc.
• Type specifiers:
  • INTEGER - Integer values
  • SCALAR - Floating-point values
  • VECTOR(n) - n-element vectors
  • MATRIX(r,c) - r×c matrices
  • BOOLEAN - Logical values
  • CHARACTER(n) - Character strings
  • BIT(n) - Bit strings
  • EVENT - Synchronisation events
• Real-time keywords: SCHEDULE, WAIT, SIGNAL, PRIORITY, TERMINATE
• Logical operators: NOT, AND, OR

Multi-line Format

HAL/S supports a unique multi-line format for mathematical notation:

E           2
M    X = Y
S     I

This represents X = Y² (Y subscript I squared), allowing source code to resemble mathematical equations.

Documentation Sources

This extension was developed using official NASA documentation:

1. HAL/S Language Specification (NASA, 1976)

   • Primary language reference

2. HAL/S Programmer's Guide (Intermetrics, 1978)

   • Programming techniques and examples

3. Programming in HAL/S (NASA, 1978)

   • Tutorial and programming manual

Configuration

Setting	Description	Default
hals.pythonPath	Path to Python interpreter	python
hals.serverPath	Path to LSP server script	(bundled)
hals.trace.server	Trace level for debugging	off

Requirements

• Visual Studio Code 1.75.0 or later
• Python 3.8 or later

Known Limitations

• Multi-line E/S/M format parsing is simplified (subscript/exponent lines are currently skipped)
• The parser handles core HAL/S constructs but may not cover all implementation-specific extensions
• Some advanced COMPOOL patterns may not be fully supported

Licence

Copyright 2025 Zane Hambly

Licensed under the Apache Licence, Version 2.0. See LICENSE for details.

Contributing

Contributions are welcome! Please open an issue or pull request on GitHub.

Related Projects

If you've found yourself oddly satisfied by a language that handles vectors and matrices natively because astronauts shouldn't have to think about loop indices during re-entry, you might appreciate:

• JOVIAL J73 LSP - The US Air Force's real-time language. Same era, same contractors (Intermetrics did both), different altitude ceiling. JOVIAL keeps aircraft from crashing into the ground; HAL/S keeps spacecraft from crashing into the ground at considerably higher speeds.

• CMS-2 LSP - The US Navy's tactical language. For when you need real-time computing but prefer to stay attached to a planet. Aegis cruisers and submarines run this. No astronauts required.

• CORAL 66 LSP - The British equivalent. Developed at the Royal Radar Establishment, Malvern, presumably whilst discussing the weather. Powers Tornado aircraft and, one assumes, runs perfectly well in drizzle.

• Minuteman Guidance Computer Emulator - An emulator for the D17B/D37C guidance computers in Minuteman ICBMs. Also goes to space, technically. Just the once. And rather more quickly.

• Minuteman Assembler - Two-pass assembler for the D17B/D37C. For the other way of getting to space. No heat tiles required. No return trip either.

Contact

Questions? Found an issue? Worked on the actual Shuttle software and want to tell me everything I got wrong?

zanehambly@gmail.com - Ground control is standing by. All transmissions welcome.

Acknowledgements

• NASA (National Aeronautics and Space Administration)
• Intermetrics, Inc. (original HAL/S compiler developers)
• Space Shuttle Program flight software engineers