elps: Skill for Claude Code

/add-linter-check — New Lint Analyzer Skill

Adds a new static analysis check to the ELPS linter (lint/, run by elps lint, the LSP, and CI). This is a prescriptive workflow touching three Go files plus docs/lint-checks.md.

For Go-side invariants over elps's own source, use /elpsvet instead.

Trigger

Use when asked to add a new lint check or analyzer for ELPS source, when a new builtin/op/macro has structural requirements (see /implement), or when a behavior change needs a static migration diagnostic.

Workflow

1. Design the Check

Before writing code, answer:

• What pattern does this check detect? (name it with kebab-case, e.g., unused-import)
• Is it a simple per-expression check (use WalkSExprs) or context-sensitive (use custom walker)?
• What's the diagnostic message? Keep it concise and actionable.
• What are the false positive risks? Plan mitigations.

2. File 1: lint/analyzers.go — Define the Analyzer

Add a new exported variable following this pattern:

var AnalyzerMyCheck = &Analyzer{
	Name: "my-check",
	Doc:  "Check that ... (one-line description used by --list)",
	Run: func(pass *Pass) error {
		WalkSExprs(pass.Exprs, func(sexpr *lisp.LVal, depth int) {
			head := HeadSymbol(sexpr)
			if head != "target-form" {
				return
			}
			// Check logic here
			argc := ArgCount(sexpr)
			if argc < 2 {
				src := SourceOf(sexpr)
				pass.Report(Diagnostic{
					Message: "descriptive error message",
					Pos:     posFromSource(src.Source),
				})
			}
		})
		return nil
	},
}

Available helpers:

• WalkSExprs(exprs, fn) — Walk all s-expressions, calls fn with each sexpr and depth
• Walk(exprs, fn) — Walk ALL nodes (not just s-expressions)
• HeadSymbol(sexpr) — Get the operator name (e.g., "if", "defun")
• ArgCount(sexpr) — Count arguments (excludes the operator)
• SourceOf(v) — Get source location, falling back to first child if needed
• posFromSource(loc) — Convert *token.Location to Position
• pass.Report(diag) — Report a diagnostic
• pass.Reportf(source, format, args...) — Printf-style diagnostic