LSP & Editor Guide

plgl is a Language Server for the patch-prolog language. It gives any LSP-capable editor real-time diagnostics, completion, hover docs, and go-to-definition over stdio. Unlike plgc, the server links only the parser — no clang, no runtime — so it’s small and starts instantly.

What it provides

Diagnostics — syntax/parse errors as you type, plus warnings for calls to predicates defined nowhere, with did-you-mean suggestions (e.g. a typo’d parnet/2 suggests parent/2). These are warnings in the editor; to make them hard build failures, use plgc --deny-undefined (see Compiler Usage).
Completion — builtins, the stdlib, and the predicates defined in the current buffer.
Hover — a one-line doc for builtins, and the clause head for user-defined predicates.
Go-to-definition — jumps to a predicate’s first clause.

Completion, hover, and the undefined-predicate check all draw on the same sources as the compiler (the shared builtin table, the stdlib, the frontend parser), so the editor agrees with what plgc accepts.

Installing `plgl`

The toolchain isn’t on crates.io yet, so build from source. The server needs only the parser, so you can install just it:

git clone https://git.navicore.tech/navicore/patch-prolog
cd patch-prolog
cargo install --path crates/lsp

Or install the whole toolchain at once:

just install        # plgc, plgr, plgl

Verify with plgl --version. The server speaks LSP over stdio; you don’t run it directly — your editor launches it.

Neovim

The companion plugin patch-prolog.nvim wires up the LSP along with filetype detection (.pl, .plg, .pro → prolog), syntax highlighting, and indentation. It needs Neovim 0.10+ and plgl on your PATH.

With lazy.nvim:

{
  "navicore/patch-prolog.nvim",
  ft = "prolog",
  opts = {},
}

Or configure it directly:

require("plgl").setup({
  -- cmd = { "plgl" },              -- override the binary path/args if needed
  on_attach = function(client, bufnr)
    local map = vim.keymap.set
    map("n", "gd", vim.lsp.buf.definition, { buffer = bufnr })
    map("n", "K",  vim.lsp.buf.hover,      { buffer = bufnr })
  end,
})

Neovim’s built-in detection maps .pl to Perl; the plugin overrides that to prolog.

Any other LSP client

plgl is a standard stdio language server — any client can drive it with three things:

Command: plgl (no arguments; communicates over stdin/stdout).
Language / filetype: prolog.
Root directory: the project root — .git is the usual marker.

For example, a bare Neovim client without the plugin:

vim.lsp.start({
  name = "plgl",
  cmd = { "plgl" },
  root_dir = vim.fs.root(0, { ".git", "Cargo.toml" }),
})

The same three parameters translate to VS Code, Emacs eglot/lsp-mode, Helix (languages.toml), and others.

Known limitations

Hover and go-to-definition work on identifier names. Operator-named builtins (=.., @<, \+) aren’t hoverable — the cursor-word extraction only spans identifier characters.
Diagnostics are computed per file from the open buffer; cross-file project resolution is not modeled (a predicate defined in another file the buffer doesn’t include reads as undefined).

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