# Haskell Parser Combinators

This note covers `12-haskell-parser-combinators/`, which parses a tiny deploy-command language with Megaparsec.

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## 1. Why Parser Combinators Matter

Parser combinators let you build a parser out of smaller parsers:

- parse one token,
- combine it with another parser,
- choose between alternatives, and
- repeat parts that can appear many times.

That makes them a very Haskell-shaped tool: you write small functions, compose them, and end up with a parser for a whole language.

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## 2. What This Example Shows

The example defines parsers for:

- the environment,
- identifiers,
- tag lists, and
- the full deploy command.

The full parser then composes those pieces with sequencing, `choice`, `many`, and `sepBy1`.

That is the main intermediate idea: treat a parser as a reusable value, not a one-off block of string handling code.

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## 3. Commands to Try

```bash
cd 12-haskell-parser-combinators

nix develop
cabal run
cabal run -- deploy api production tags=blue,stable
cabal test

nix build
./result/bin/mini-parser deploy api production tags=blue,stable

nix run . -- deploy api production tags=blue,stable
nix flake check
```