aspls — Answer Set Programming (Clingo)
Language support for Answer Set Programming in the ASP-Core-2 / Clingo dialect.
Works with .lp and .asp files in VS Code, Cursor, VSCodium, and compatible editors.
Why aspls: one extension that combines language intelligence (diagnostics, completion, hover, go-to-definition / find-references, semantic + rainbow highlighting, optional learner mode) with a Clingo runner (bundled WASM or PATH binary, Solver sidebar). That avoids stacking a highlight-only extension with a separate run-oriented tool.
Repository: github.com/paolaguarasci/aspls
At a glance
Features
| Feature |
What you get |
| Run Clingo |
Compute first or all answer sets (editor title buttons, context menu, Command Palette) |
| ASP sidebar — Solver |
Activity Bar ASP → Solver: First / All / Config runs, answer sets, errors, re-run; Controls for models, native Clingo path, and additional files |
| ASP sidebar — Predicates |
ASP → Predicates: active-file predicates nested by role → occurrence (powers Outline); toolbar Show Workspace Predicates |
| PATH or WASM |
Bundled clingo-wasm by default; optional Clingo binary from PATH |
| Syntax highlighting |
Atoms, variables, comments, directives, operators |
| Semantic highlighting |
Different colors for facts, rule heads, rule bodies, constraints, #show, #minimize |
| Rainbow predicates |
Optional underline color per predicate name (stable across the file) |
| Diagnostics |
Syntax errors from the ASP parser; optional Clingo-backed checks |
| IntelliSense |
Predicate completion from the workspace / config file pool |
| Hover |
Name, arity, occurrence counts; asp-lsp-style %*…*% docstrings; definition line + preceding comment |
| Go to Definition |
Jump to facts and rule heads (cross-file) |
| Find References |
All occurrences of a predicate in the pool |
| Learner mode |
Optional rule-order and missing-comment Information hints, plus quick fixes (off by default) |
| Code Cookbook |
Browse working ASP patterns and insert at cursor or open as a new .lp file |
| Snippets |
Templates for #show, #const, #minimize, aggregates, choice rules, weak constraints |
Known limits (ASP grammar subset)
The language server parses a growing subset of Clingo / ASP-Core-2. Unsupported constructs get syntax diagnostics even when Clingo itself would accept them.
| Construct |
Status |
| Facts, rules, integrity constraints |
Supported |
Default negation (not) |
Supported |
Comparisons and #count / #sum / #max / #min |
Supported |
#const, #show, #minimize, #maximize |
Supported |
Choice rules { … } |
Supported |
Weak constraints (:~ … . [w@p, …]) |
Supported |
#include, #external, #heuristic, #script, #program |
Supported |
| Variable bounds on choice |
Supported |
Snippets and the Code Cookbook may show patterns ahead of the parser; prefer this table when diagnostics disagree with Clingo.
Quick start
- Install aspls from the VS Marketplace or Open VSX.
- Make sure Python 3 is available on your PATH (or set
aspls.pythonPath) for the language server.
- Open a
.lp file — the language server starts on first use and sets up a local venv automatically.
- Click the play / run all icons in the editor title bar, or use the Command Palette:
- aspls: Compute first answer set
- aspls: Compute all answer sets
- Results open in the Activity Bar ASP → Solver view.
Optional: install Clingo on PATH for extra diagnostics and native solver via aspls.clingo.usePath.
Example
% Birds that are not penguins can fly
bird(tweety).
penguin(pingu).
flies(X) :- bird(X), not penguin(X).
#show flies/1.
- Facts (
bird, penguin) — bold green
- Rule head (
flies) — bold blue
- Rule body — muted;
not penguin italic when negated
#show — gold
Tutorial projects under examples/ and the Code Cookbook align with the Potassco Guide and ASP courses (teaching.potassco.org): birds → choice → optimization → graph coloring, Sudoku, planning. Full mapping table in the repository README.
Clingo config
Workspace file aspls.clingo.json is the canonical source for additionalFiles, models, threads, and customArgs used by both the language server and the Clingo runner.
Create it with aspls: Initialize Clingo config file.
{
"models": 0,
"threads": 1,
"customArgs": "",
"additionalFiles": ["facts.lp"]
}
additionalFiles in config |
LSP pool |
Runner file set |
Key absent / null |
Full workspace discovery |
Active file only |
[] (explicit empty) |
Active file only |
Active file only |
["a.lp", "b.lp"] |
Active + listed files |
Active + listed files |
Path resolution: active file directory → workspace root → active-directory candidate as-is.
aspls.clingo.additionalFiles in Settings is deprecated — copied only when creating the config file; not read at runtime.
Before every run, aspls preflights missing files, invalid models, and missing configured PATH binaries.
Capability matrix (WASM vs PATH)
| Feature |
Bundled WASM |
Native PATH |
| Basic programs / answer sets |
yes |
yes |
Multi-file via additionalFiles |
limited |
yes |
models / -n |
yes |
yes |
--const / -c |
yes |
yes |
Threads (-t) |
limited |
yes |
Output control (--outf, -q, stats) |
no |
yes |
| Advanced CLI |
no |
yes |
WASM multi-file limits
Bundled clingo-wasm accepts a single program string — not separate input files. When aspls.clingo.usePath is false, aspls:
- Expands
#include "…" in the active file before the run.
- Concatenates
additionalFiles after the primary source (% === filename === markers).
Typical fact/rule splits (e.g. examples/04_multi_file/) work; per-file #program boundaries and advanced modular encodings may differ from native Clingo. Enable aspls.clingo.usePath for native multi-file semantics.
Docstrings & learner mode
Predicate docstrings
%*
#bird(X).
A flying animal (unless it is a penguin).
#parameters
- X : The individual.
*%
bird(tweety).
Learner mode (aspls.learnerMode)
When enabled: Information hints for rule order and missing % comments, with Fix Order and Add preceding comment quick fixes.
onceUsed (aspls.diagnostics.onceUsed)
Warns when a predicate appears only once as a use (rule body / constraint). Skips lone definitions and #show / #minimize-linked predicates.
Settings
| Setting |
Default |
Description |
aspls.pythonPath |
"" |
Path to Python 3 |
aspls.rainbowPredicates |
true |
Rainbow underline per predicate |
aspls.diagnostics.onceUsed |
true |
Warn on single-use body predicates |
aspls.learnerMode |
false |
Learner Information hints |
aspls.clingo.usePath |
false |
Use PATH instead of WASM |
aspls.clingo.path |
"" |
Optional Clingo binary path |
aspls.clingo.models |
1 |
Default model count (0 = all) |
aspls.clingo.threads |
1 |
Clingo -t |
aspls.clingo.customArgs |
"" |
Extra CLI args |
aspls.clingo.additionalFiles |
[] |
Deprecated (init migration only) |
aspls.clingo.configFile |
aspls.clingo.json |
Config file name |
Release checklist (maintainers)
Before a Marketplace / Open VSX release after pool or runner changes:
npm test in client/pytest in server/- Manual:
additionalFiles: [] → file-local analysis; remove key → workspace pool
- Manual: missing
additionalFiles path → Solver preflight error
- Manual: WASM + fragile
customArgs → capability warning; usePath → warning gone
- Manual: edit
aspls.clingo.json while .lp open → diagnostics refresh
Publish:
npm run publish:marketplace
npm run publish:openvsx
Feedback
Issues and contributions: github.com/paolaguarasci/aspls.
License
MIT © Paola Guarasci
