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(ns clojure-sql.writer
(:refer-clojure :exclude [sequence]))
;; A small writer monad implementation, for what we need
(defn return [x]
(fn [s] [x s]))
(defn bind [mv f]
{:pre [(not (nil? mv))]}
(fn [s]
(let [[x s2] (mv s)]
((f x) s2))))
(defn tell [val]
(fn [s] [nil (conj s val)]))
(defn join [mv]
(bind mv identity))
(defn sequence
([] (return nil))
([mv & mvs]
{:pre [(not (nil? mv))]}
(bind mv
(fn [x]
(bind (apply sequence mvs)
(fn [xs]
(return (cons x xs))))))))
(defn lift [f]
(fn [& args]
(bind (apply sequence args)
(fn [s]
(return (apply f s))))))
(defn p-lift [f & args]
(lift (apply partial f args)))
(defn >>
([arg]
arg)
([arg1 & args]
(bind arg1
(fn [x]
(apply >> args)))))
(defn do-m*
([] (throw (ex-info "No." {})))
([& args]
(or (if (nil? (next args))
(first args))
(if (= (first args) :let)
`(let ~(second args)
~(apply do-m* (nnext args))))
(if (every? #(% (second args)) [symbol? #(= (name %) "<-")])
(let [[var <- val & others] args]
`(bind ~val
(fn [~var]
~(apply do-m* others)))))
`(bind ~(first args)
(fn [_#]
~(apply do-m* (next args)))))))
(defmacro do-m [& args]
(apply do-m* args))
(defmacro do [& args]
(apply do-m* args))
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