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Haskell + Servant

Servant for type-level API design.

BackendComplex

Stack Components

LanguageGHC 9.8
FrameworkServant 0.20
DBpersistent
DBPostgreSQL 16

Why

APIs as types, automatic docs, type-safe clients. Node.js, Go, and Python are the top 3 backend languages (Stack Overflow 2024).

Go's goroutines handle 100k+ concurrent connections per process; Node's event loop excels at I/O-bound workloads.

When

Use for correctness-critical APIs. Avoid for rapid dev.

How

1. stack new app servant 2. Define API type 3. Implement server 4. stack run 5. Add environment configuration — cp .env.example .env && edit values 6. Run tests — npm test or pnpm test to verify setup 7. Deploy — git push to trigger CI/CD or manual deploy

Example

type API = 'users' :> Get '[JSON] [User] server :: Server API server = getUsers // Haskell + Servant — usage example import { HaskellServant } from "haskell-servant"; const result = await haskellservant({ input: "data" }); console.log(result);

Common Problems

  • ⚠Type-level programming — use TypeApplications
  • ⚠Build times — use ghci for fast feedback
  • ⚠Configuration drift between environments — use infrastructure-as-code (Terraform/Pulumi) to keep dev/staging/prod identical

Best Practices

  • ✓Use servant-docs for API docs
  • ✓Leverage generics for boilerplate
  • ✓Set up health checks and graceful shutdown — handle SIGTERM to drain in-flight requests before exit

FAQ

What is Haskell + Servant and what projects is it for?

Servant for type-level API design. It pairs layered technologies for end-to-end type safety and out-of-the-box deploys, fitting everything from MVPs to production SaaS.

How do I spin up a working demo with Haskell + Servant in 10 minutes?

Two steps: (1) stack new app servant; (2) Define API type. Get the local dev server running, then wire one real data source to verify the end-to-end loop.

What is the most common pitfall with Haskell + Servant and how do I avoid it?

The most common pitfall is: Type-level programming — use TypeApplications. Avoid it by adding the matching checklist to your PR template and running type-check + lint + unit tests in CI — three gates before merge.

What are the best practices for Haskell + Servant?

Best practices for Haskell + Servant include: Use servant-docs for API docs; Leverage generics for boilerplate; Set up health checks and graceful shutdown — handle SIGTERM to drain in-flight requests before exit. The first one — "Use servant-docs for API docs" — should be set up at project init to avoid costly rework later.

When should I NOT choose Haskell + Servant?

Pick something else in three cases: (1) the team has zero experience with the core framework and the deadline is tight (learning-curve risk); (2) it's a pure content/marketing site (Astro is lighter); (3) you need very high throughput (>10k RPS) or strict-consistency microservices (Go/Rust). Haskell + Servant shines for mid-to-high complexity full-stack and API work — don't over-engineer simple static pages with it.