Comparison

Expound's error messages are more verbose than the clojure.spec messages, which can help you quickly determine why a value fails a spec. Here are some examples.

---

Nested data structures

If the invalid value is nested, Expound will help locate the problem

Specs

(s/def :db/id clojure.core/pos-int?)
(s/def :db/ids (s/coll-of :db/id))
(s/def :app/request (s/keys :req-un [:db/ids]))

Value

{:ids [123 "456" 789]}

clojure.spec message

"456" - failed: pos-int? in: [:ids 1] at: [:ids] spec: :db/id

Expound message

-- Spec failed --------------------

  {:ids [... "456" ...]}
             ^^^^^

should satisfy

  pos-int?

-------------------------
Detected 1 error

---

Missing keys

If a key is missing from a map, Expound will display the associated spec

Specs

(s/def :address.west-coast/city clojure.core/string?)
(s/def :address.west-coast/state #{"CA" "WA" "OR"})
(s/def :app/address (s/keys :req-un [:address.west-coast/city :address.west-coast/state]))

Value

{}

clojure.spec message

{} - failed: (contains? % :city) spec: :app/address
{} - failed: (contains? % :state) spec: :app/address

Expound message

-- Spec failed --------------------

  {}

should contain keys: :city, :state

| key    | spec              |
|========+===================|
| :city  | string?           |
|--------+-------------------|
| :state | #{"CA" "WA" "OR"} |

-------------------------
Detected 1 error

---

Set-based specs

If a value doesn't match a set-based spec, Expound will list the possible values

Specs

(s/def :address.west-coast/city clojure.core/string?)
(s/def :address.west-coast/state #{"CA" "WA" "OR"})
(s/def :app/address (s/keys :req-un [:address.west-coast/city :address.west-coast/state]))

Value

{:city "Seattle", :state "ID"}

clojure.spec message

"ID" - failed: #{"CA" "WA" "OR"} in: [:state] at: [:state] spec: :address.west-coast/state

Expound message

-- Spec failed --------------------

  {:city ..., :state "ID"}
                     ^^^^

should be one of: "CA", "OR", "WA"

-------------------------
Detected 1 error

---

Grouping

Expound will group alternatives

Specs

(s/def :address.west-coast/zip (s/or :str clojure.core/string? :num clojure.core/pos-int?))

Value

:98109

clojure.spec message

:98109 - failed: string? at: [:str] spec: :address.west-coast/zip
:98109 - failed: pos-int? at: [:num] spec: :address.west-coast/zip

Expound message

-- Spec failed --------------------

  :98109

should satisfy

  string?

or

  pos-int?

-------------------------
Detected 1 error

---

Predicate descriptions

If you provide a predicate description, Expound will display them

Specs

(def email-regex #"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,63}$")
(defn valid-email? [s] (re-matches email-regex s))
(s/def :app.user/email (s/and string? valid-email?))
(expound/defmsg :app.user/email "should be a valid email address")

Value

"@example.com"

clojure.spec message

"@example.com" - failed: valid-email? spec: :app.user/email

Expound message

-- Spec failed --------------------

  "@example.com"

should be a valid email address

-------------------------
Detected 1 error

---

Too few elements in a sequence

If you are missing elements, Expound will describe what must come next

Specs

(s/def :app/ingredient (s/cat :quantity clojure.core/number? :unit clojure.core/keyword?))

Value

[100]

clojure.spec message

() - failed: Insufficient input at: [:unit] spec: :app/ingredient

Expound message

-- Syntax error -------------------

  [100]

should have additional elements. The next element ":unit" should satisfy

  keyword?

-------------------------
Detected 1 error

---

Too many elements in a sequence

If you have extra elements, Expound will point out which elements should be removed

Specs

(s/def :app/ingredient (s/cat :quantity clojure.core/number? :unit clojure.core/keyword?))

Value

[100 :teaspoon :sugar]

clojure.spec message

(:sugar) - failed: Extra input in: [2] spec: :app/ingredient

Expound message

-- Syntax error -------------------

  [... ... :sugar]
           ^^^^^^

has extra input

-------------------------
Detected 1 error