Add :decimal schema

src/malli/core.cljc

@@ -824,6 +824,7 @@
 (defn -int-schema [] (-simple-schema {:type :int, :pred int?, :property-pred (-min-max-pred nil)}))
 (defn -float-schema [] (-simple-schema {:type :float, :pred float?, :property-pred (-min-max-pred nil)}))
 (defn -double-schema [] (-simple-schema {:type :double, :pred double?, :property-pred (-min-max-pred nil)}))
+(defn -decimal-schema [] (-simple-schema {:type :decimal, :pred #?(:clj decimal? :cljs (constantly false)), :property-pred (-min-max-pred nil)}))
 (defn -boolean-schema [] (-simple-schema {:type :boolean, :pred boolean?}))
 (defn -keyword-schema [] (-simple-schema {:type :keyword, :pred keyword?}))
 (defn -symbol-schema [] (-simple-schema {:type :symbol, :pred symbol?}))
@@ -2958,6 +2959,7 @@
    :int (-int-schema)
    :float (-float-schema)
    :double (-double-schema)
+   :decimal (-decimal-schema)
    :boolean (-boolean-schema)
    :keyword (-keyword-schema)
    :symbol (-symbol-schema)

src/malli/generator.cljc

@@ -418,6 +418,7 @@
 (defmethod -schema-generator :int [schema options] (gen/large-integer* (-min-max schema options)))
 (defmethod -schema-generator :double [schema options] (double-gen schema options))
 (defmethod -schema-generator :float [schema options] (double-gen schema options))
+#?(:clj (defmethod -schema-generator :decimal [schema options] (gen-fmap bigdec (double-gen schema options))))
 (defmethod -schema-generator :boolean [_ _] gen/boolean)
 (defmethod -schema-generator :keyword [_ _] gen/keyword)
 (defmethod -schema-generator :symbol [_ _] gen/symbol)

src/malli/transform.cljc

@@ -334,6 +334,7 @@
        :int -string->long
        :float -string->float
        :double -string->double
+       #?@(:clj [:decimal -string->decimal])
        :boolean -string->boolean
 
        :> -string->long
@@ -369,6 +370,7 @@
        :int -any->string
        :float -any->string
        :double -any->string
+       #?@(:clj [:decimal -any->string])
        ;:boolean -any->string
 
        :> -any->string

test/malli/core_test.cljc

@@ -2212,6 +2212,24 @@
                                [1.1 3.1 mt/string-transformer [:double {:encode/string {:enter inc, :leave inc}}]]]
                       :ast {:type :double, :properties {:min 1.0, :max 4.0}}
                       :form [:double {:min 1.0, :max 4.0}]}
+             #?@(:clj [:decimal {:schema [:decimal {:min 1.0M, :max 4.0M}]
+                                 :validate {:success [1.0M 2.2M 4.0M]
+                                            :failure [nil "invalid" 0.5M 1.0]}
+                                 :explain [[1.0M]
+                                           [false {:schema [:decimal {:min 1.0M, :max 4.0M}]
+                                                   :value false
+                                                   :errors [{:path []
+                                                             :in []
+                                                             :schema [:decimal {:min 1.0M, :max 4.0M}]
+                                                             :value false}]}]]
+                                 :decode [["1.1" 1.1M mt/string-transformer]
+                                          ["1.1" "1.1" mt/json-transformer]
+                                          [1.1M 3.1M mt/string-transformer [:decimal {:decode/string {:enter inc, :leave inc}}]]]
+                                 :encode [[1.1M "1.1" mt/string-transformer]
+                                          [1.1M 1.1M mt/json-transformer]
+                                          [1.1M 3.1M mt/string-transformer [:decimal {:encode/string {:enter inc, :leave inc}}]]]
+                                 :ast {:type :decimal, :properties {:min 1.0M, :max 4.0M}}
+                                 :form [:decimal {:min 1.0M, :max 4.0M}]}])
              :keyword {:schema :keyword
                        :validate {:success [:abba :user/abba]
                                   :failure [nil "invalid"]}

test/malli/generator_test.cljc

@@ -345,6 +345,11 @@
       [:set {:min 1, :gen/min 10, :max 100, :gen/max 200} int?]
       [:string {:min 1, :gen/min 10, :max 100, :gen/max 200}])))
 
+#?(:clj
+   (deftest decimal-generator-test
+     (is (every? decimal? (mg/sample [:decimal {:min 0.0M, :max 1.0M}] {:size 100})))
+     (is (every? #(<= 0.0M % 1.0M) (mg/sample [:decimal {:min 0.0M, :max 1.0M}] {:size 100})))))
+
 (deftest protocol-test
   (let [values #{1 2 3 5 8 13}
         schema (reify