Halfway there.

.travis.yml

@@ -1,4 +1,5 @@
 language: clojure
+dist: precise
 lein: lein2
 script: lein2 midje :config .midje-grading-config.clj
 jdk:

src/one_function_to_rule_them_all.clj

@@ -1,19 +1,36 @@
 (ns one-function-to-rule-them-all)
 
 (defn concat-elements [a-seq]
-  :-)
+  (reduce concat [] a-seq))
 
 (defn str-cat [a-seq]
-  :-)
+  (if (empty? a-seq)
+    ""
+    (reduce (fn [b-seq x] (str b-seq " " x)) a-seq)))
+
+(defn my-interpose2 [x a-seq]
+  (if (empty? a-seq)
+    []
+    (reduce (fn [b-seq y] (conj b-seq x y)) a-seq)))
 
 (defn my-interpose [x a-seq]
-  [:-])
+  (cond
+    (empty? a-seq)
+      []
+    (= 1 (count a-seq))
+      a-seq
+    :else
+      (reduce (fn [b-seq y] (conj b-seq x y)) a-seq)))
 
 (defn my-count [a-seq]
-  :-)
+  (let [counter (fn [count e]
+                  (if e (inc count) count))]
+    (reduce counter 0 a-seq)))
 
 (defn my-reverse [a-seq]
-  [:-])
+  (if (empty? a-seq)
+    []
+    (reduce cons a-seq)))
 
 (defn min-max-element [a-seq]
   [:-])
@@ -27,17 +44,24 @@
 (defn parity [a-seq]
   [:-])
 
-(defn minus [x]
-  :-)
+(defn minus
+  ([x] (* -1 x))
+  ([x y] (- x y)))
 
-(defn count-params [x]
-  :-)
+(defn count-params [& more]
+  (count more))
 
-(defn my-* [x]
-  :-)
+(defn my-*
+  ([] 1)
+  ([x] x)
+  ([x y] (* x y))
+  ([x y & more] (reduce * (* x y) more)))
 
-(defn pred-and [x]
-  (fn [x] :-))
+(defn pred-and
+  ([] (fn [a] a))
+  ([x] (fn [a] (x a)))
+  ([x y] (fn [a] (and (x a) (y a))))
+  ([x y & more] (reduce (fn [a] (and (x a) (y a))) more)))
 
 (defn my-map [f a-seq]
-  [:-])
+  [:-])