DSL Editor

The BPC source editor — CodeMirror 6, a Lezer-generated grammar, syntax highlighting tuned for prose-shaped charts, and two-way sync with the visual panels.

Why this matters

Blueprint Chart is text-first. Every chart in the editor has a .bpc source under the hood, and any change you make through the visual panels — picking a palette, dragging an annotation, reordering scenes — is reflected back in that source. The DSL editor is the surface where authors who prefer code can stay in code, and the surface where a journalist swapping numbers can do it without ever opening a panel. CodeMirror 6 powers the editor; a separate Lezer grammar drives the syntax highlighting.

Quickstart

Type .bpc directly in the editor's left pane. The right pane re-renders on every parse-clean keystroke:

chart line {
  title = "2024 was the hottest year on record"
  description = "Deviation from the 1951–1980 average, in °C"
  source = "NASA GISS"
  sourceUrl = "https://data.giss.nasa.gov/gistemp/"
  colors = "#e15759"
  autoContrast = false
  allowDarkMode = true
  interpolation = "monotoneX"
  lineSymbols = true
  lineSymbolShape = "circle"
  lineSymbolShowOn = "firstLast"

  data {
    "1980" = 0.26
    "1985" = 0.12
    "1990" = 0.45
    "1995" = 0.45
    "2000" = 0.42
    "2005" = 0.68
    "2010" = 0.72
    "2015" = 0.9
    "2020" = 1.02
    "2024" = 1.29
  }

  annotation "2015" {
    id = "2o3cx"
    text = "2015 Paris Agreement to limit global warming to 1.5°C "
    maxWidth = 224
    showLine = true
    lineStyle = curve-right
    showArrow = true
    showCircle = true
  }
}

From the sample library

This is packages/lib/src/samples/temperature-anomaly.bpc — a good stress test for the highlighter because it mixes every common token class: keywords (chart, data, annotation), identifiers (autoContrast, lineSymbolShape), strings, numbers, enum values (monotoneX, firstLast, curve-right), and booleans. The fold ranges align with each top-level block.

Line comments use // and stop at end-of-line. There are no block comments.

How it works

The editor runs two parsers for the same DSL surface, and the trade-off is deliberate:

Parser	Package	Job	Generation
Peggy	@blueprint-chart/lib	AST for chart computation at runtime — full semantics.	make build-parser
Lezer	@blueprint-chart/editor	Incremental parse tree for syntax highlighting.	pnpm --filter @blueprint-chart/editor build:parser

Both grammars describe the same language. The Peggy one is the source of truth for correctness (parses, validates, round-trips); the Lezer one is built for fast incremental re-parse on every keystroke so the editor never blocks.

The CodeMirror 6 stack pulls in @codemirror/view, @codemirror/state, @codemirror/language, and @lezer/highlight. The DSL language module lives at packages/editor/src/dsl-lang/ and exposes three entry points:

• bpcLanguage() — returns a CodeMirror LanguageSupport you install on the editor instance.
• bpcHighlighter — a syntaxHighlighting extension pre-wired to the class-based highlighter.
• highlightDsl(code) — one-shot server-style highlight, used by read-only previews; returns HTML.

The Lezer parser tags DSL keywords (chart, data, colorize, highlight, areafill, annotation, range, note, series, scene, step, transform) and lexical tokens (Identifier, String, Number, Percentage, Equals, LineComment, braces). Each tag maps to a token class in packages/editor/src/dsl-lang/highlight.scss, with separate light- and dark-mode rules driven by the --bc-syn-* CSS custom properties.

Two-way sync between DSL and panels

The editor keeps the DSL text and the visual panels in lockstep through two composables:

• useDslSync — DSL → config and config → DSL. On every keystroke, a debounced parse runs; on success, the resulting AST is diffed against the chartConfig store and applied. The reverse direction kicks in when a user edits via a panel: the chart state is serialised back to DSL and pushed into the editor with a cursor-preserving patch.
• useDslOutput — formats the current chart state into its canonical DSL string. This is what the "Copy as DSL" button and the export panel consume.

Because the grammar round-trips cleanly (parse(serialize(parse(x))) is structurally equal to parse(x)), the sync loop is stable — a panel-driven change does not surprise the user with reformatted whitespace, and a DSL-driven change does not lose unknown property keys.

Recipes

Embed the BPC language in your own CodeMirror editor

bpcLanguage() and bpcHighlighter are plain CodeMirror 6 extensions — they fit into any consumer that already builds a CodeMirror view:

import { EditorView, basicSetup } from 'codemirror'
import { bpcLanguage, bpcHighlighter } from '@/dsl-lang'

const view = new EditorView({
  doc: '',
  extensions: [
    basicSetup,
    bpcLanguage(),
    bpcHighlighter,
  ],
  parent: document.querySelector('#editor')!,
})

Highlight a read-only DSL block

For a docs page, a "view source" tab, or a tooltip preview, highlightDsl(code) returns ready-to-inject HTML:

import { highlightDsl } from '@/dsl-lang'

const html = highlightDsl(`chart line-multi {
  title = "Germany stagnated while the US and China bounced back"
  description = "Annual percentage change in real GDP"
  source = "IMF World Economic Outlook"
  colorPalette = "SolLeWitt"
  legend = false
  tooltips = true

  annotation "2020" {
    text = "COVID-19 recession"
    dy = -10
    showArrow = true
  }

  data {
    _series = "United States","China","Germany"
    "2018" = 2.9,6.7,1.0
    "2020" = -2.8,2.2,-3.7
    "2024" = 2.8,5.0,-0.2
  }
}`)

document.querySelector('#preview')!.innerHTML = html

From the sample library

The DSL string is trimmed from packages/lib/src/samples/gdp-growth.bpc (full sample has the 2018–2024 yearly series). Good stress-case for the highlighter — multi-series data, palette name, a negative number, an annotation block.

This skips the editor surface entirely and is the right tool when the user shouldn't be able to type.

Parse the editor's content programmatically

To act on the DSL outside the editor — validate, transform, or feed it to a renderer — pair bpcLanguage() with the lib's parse():

import { parse } from '@blueprint-chart/lib'

try {
  const ast = parse(view.state.doc.toString())
  // ast.chartType, ast.properties, ast.data, ast.scenes …
} catch (err) {
  // SyntaxError with 1-indexed location { line, column }
}

Errors are SyntaxError instances with a 1-indexed location field. CodeMirror's lintGutter extension is the natural place to surface them.

Read the Lezer tree directly

Autocomplete is not exposed by default, but the Lezer parse tree is available if you want to write a completion source, a custom folding range provider, or any other syntax-driven feature:

import { syntaxTree } from '@codemirror/language'

const tree = syntaxTree(view.state)
tree.iterate({
  enter(node) {
    if (node.name === 'Property') {
      // … node.from / node.to give you the document range
    }
  },
})

Files in the package

The DSL language module ships inside @blueprint-chart/editor:

• packages/editor/src/dsl-lang/bpc.grammar — Lezer grammar source.
• packages/editor/src/dsl-lang/bpc-parser.js — generated Lezer parser (committed to the repo).
• packages/editor/src/dsl-lang/build.mjs — grammar build script.
• packages/editor/src/dsl-lang/index.ts — exports bpcLanguage(), bpcHighlighter, highlightDsl().
• packages/editor/src/dsl-lang/highlight.scss — token-class colour definitions, driven by --bc-syn-* CSS variables.

API surface

The DSL editor entry points live in @blueprint-chart/editor, not in @blueprint-chart/lib. From the lib side, the parsing surface is:

Symbol (from @blueprint-chart/lib)	One-liner
parse(source)	BPC text → AST. Throws SyntaxError with location.
serialize(ast)	AST → BPC text (pretty-printed).
compactSerialize(ast)	AST → BPC text (whitespace-minimised).
propertyMap	Catalogue of recognised property keys per chart type.
ChartNode, PropertyNode, DataNode, …	AST node types — see the API reference.

From the editor side:

Symbol (from the editor's @/dsl-lang)	One-liner
bpcLanguage()	CodeMirror LanguageSupport for .bpc.
bpcHighlighter	syntaxHighlighting extension.
highlightDsl(code)	One-shot HTML highlight for read-only previews.

See also

• BPC DSL specification — the canonical language reference.
• Scenes guide — scene syntax inside the DSL.
• Data transforms guide — transforms inside the DSL.
• API reference for the lib's parse / serialize / converter helpers.