BHC Platform

BHC Platform provides curated package snapshots for the BHC (Basel Haskell Compiler) backend — the BHC equivalent of Stackage.

Overview

When using the BHC backend, BHC Platform snapshots provide a set of packages verified to build and work together. This gives you reproducible builds without manually specifying version constraints for every dependency.

Quick Start

# List available snapshots
hx bhc-platform list

# Set a snapshot for your project
hx bhc-platform set bhc-platform-2026.1

# Lock dependencies using the snapshot
hx lock

Or configure directly in hx.toml:

[compiler]
backend = "bhc"

[bhc-platform]
snapshot = "bhc-platform-2026.1"

How It Works

Embedded snapshots — BHC Platform data is embedded in hx, so no network fetch is required
Version pinning — When you run hx lock, package versions from the snapshot are pinned in the resolver
Lockfile recording — The lockfile records which snapshot was used for reproducibility
Hackage fallback — Packages not in the snapshot can be resolved from Hackage if allow_newer = true

Available Snapshots

bhc-platform-2026.1

The initial BHC Platform snapshot:

BHC version: 0.1.0
GHC compatibility: 9.8.2
Packages: ~70

Covers the core Haskell ecosystem plus specialized packages for web, numeric, and server workloads:

Category	Packages
Core	base, ghc-prim, integer-gmp, template-haskell
Text & ByteString	text, bytestring, utf8-string
Containers	containers, unordered-containers, hashable, vector
Transformers	mtl, transformers, exceptions, unliftio
Serialization	aeson, yaml, binary, cereal
Optics	lens, microlens, generic-lens
Parsing	megaparsec, attoparsec, optparse-applicative
HTTP & Web	http-client, http-types, servant, servant-server, warp, wai, wai-extra
Database	persistent, esqueleto, resource-pool
Numeric	hmatrix, statistics, massiv, random
Testing	hspec, QuickCheck, tasty, hedgehog, hspec-wai
Streaming	conduit, streaming, pipes
CLI & Logging	optparse-applicative, monad-logger, fast-logger, co-log

Configuration

Basic

[bhc-platform]
snapshot = "bhc-platform-2026.1"

With Extra Dependencies

Allow packages outside the snapshot and override specific versions:

[bhc-platform]
snapshot = "bhc-platform-2026.1"
allow_newer = true
extra_deps = { my-custom-lib = "1.0.0" }

Fields

Field	Type	Default	Description
`snapshot`	string	none	Snapshot identifier (e.g., `bhc-platform-2026.1`)
`allow_newer`	bool	`false`	Allow packages from Hackage outside the snapshot
`extra_deps`	table	`{}`	Override specific package versions

BHC Platform vs Stackage

Feature	BHC Platform	Stackage
For	BHC backend	GHC backend
Delivery	Embedded in hx	Fetched from stackage.org
Package count	~70 (curated)	~3000+
Offline	Yes	After first fetch
Configuration	`[bhc-platform]`	`[toolchain].resolver`

Use BHC Platform when [compiler].backend = "bhc". Use Stackage when using GHC.

Project Templates

The numeric and server project templates come pre-configured with BHC Platform:

# Numeric computing project
hx new numeric my-science
# → backend = "bhc", profile = "numeric", snapshot = pre-configured

# Web server project
hx new server my-api
# → backend = "bhc", profile = "server", snapshot = pre-configured

CLI Commands

Command	Description
`hx bhc-platform list`	List available snapshots
`hx bhc-platform info <platform>`	Show snapshot details
`hx bhc-platform info <platform> --packages`	Show all packages
`hx bhc-platform set <platform>`	Set snapshot in hx.toml

See hx bhc-platform for the full command reference.

Troubleshooting

Package not in snapshot

error: Could not resolve dependency: some-package

Set allow_newer = true in [bhc-platform] to allow resolving from Hackage, or add the package to extra_deps.

BHC not installed

error: BHC is not installed

Install BHC with hx toolchain install --bhc latest.

Using with GHC backend

BHC Platform snapshots are only applied when [compiler].backend = "bhc". If you’re using GHC, configure a Stackage resolver instead.