---
action: context
tool: (edit|write)
event: after
name: prefer-match-over-switch
description: Use Match from Effect instead of native switch statements
glob: '**/*.{ts,tsx}'
detector: ast
pattern: 'switch ($X) { $$$ }'
level: warning
suggestSkills:
    - effect-pattern-matching
---

# Use `Match` Instead of `switch`

```haskell
-- Transformation
switch :: a -> { case₁: b, ..., default: b }  -- non-exhaustive, fall-through risk
Match  :: a -> Matcher a b                     -- exhaustive, composable, type-safe

-- Pattern
bad :: Phase -> String
bad phase = switch phase of
  "idle"    -> "waiting"
  "running" -> "active"
  _         -> "unknown"              -- default hides new variants

good :: Phase -> String
good phase = Match.value(phase).pipe(
  Match.when("idle", \_ -> "waiting"),
  Match.when("running", \_ -> "active"),
  Match.exhaustive                    -- compiler error if variant added
)
```

```haskell
-- For tagged unions
matchTagged :: Event -> String
matchTagged = Match.value >>> pipe
  Match.tag("Created", \e -> "new: " <> e.id)
  Match.tag("Completed", \e -> "done: " <> e.id)
  Match.exhaustive
```

`switch` has fall-through semantics and non-exhaustive `default` cases that hide new variants at compile time. `Match` from Effect is exhaustive, composable, and type-safe — the compiler will error when new variants are added.

References: EF-7 in effect-first-development.md