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state.clj
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state.clj
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(ns state-flow.state
(:refer-clojure :exclude [eval get])
(:require [cats.core :as m]
[cats.monad.exception :as e]
[cats.monad.state :as state]
[cats.protocols :as p]
[cats.util :as util]))
(declare short-circuiting-context)
(defn- result-or-err [f & args]
(let [result ((e/wrap (partial apply f)) args)]
(if (e/failure? result)
result
@result)))
(defn error-catching-state [mfn]
(state/state
(fn [s]
(let [new-pair ((e/wrap mfn) s)]
(if (e/failure? new-pair)
[new-pair s]
@new-pair)))
short-circuiting-context))
(def short-circuiting-context
"Same as state monad context, but short circuits if error happens, place error in return value"
(reify
p/Context
p/Functor
(-fmap [_ f fv]
(error-catching-state
(fn [s]
(let [[v s'] ((p/-extract fv) s)]
(if (e/failure? v)
[v s']
[(result-or-err f v) s'])))))
p/Monad
(-mreturn [_ v]
(error-catching-state #(vector v %)))
(-mbind [_ self f]
(error-catching-state
(fn [s]
(let [[v s'] ((p/-extract self) s)]
(if (e/failure? v)
[v s']
((p/-extract (f v)) s'))))))
state/MonadState
(-get-state [_]
(error-catching-state #(vector %1 %1)))
(-put-state [_ newstate]
(error-catching-state #(vector % newstate)))
(-swap-state [_ f]
(error-catching-state #(vector %1 (f %1))))
p/Printable
(-repr [_]
"#<State-E>")))
(util/make-printable (type short-circuiting-context))
(defn get
"Creates a flow that returns the value of state. "
[]
(state/get short-circuiting-context))
(defn gets
"Creates a flow that returns the result of applying f (default identity)
to state with any additional args."
([]
(gets identity))
([f & args]
(state/gets #(apply f % args) short-circuiting-context)))
(defn put
"Creates a flow that replaces state with new-state. "
[new-state]
(state/put new-state short-circuiting-context))
(defn modify
"Creates a flow that replaces state with the result of applying f to
state with any additional args."
[f & args]
(state/swap #(apply f % args) short-circuiting-context))
(defn return
"Creates a flow that returns v. Use this as the last
step in a flow that you want to reuse in other flows, in
order to clarify the return value, e.g.
(def increment-count
(flow \"increments :count and returns it\"
(state/modify update :count inc)
[new-count (state/gets :count)]
(state-flow/return new-count)))"
[v]
(m/return short-circuiting-context v))
(defn invoke
"Creates a flow that invokes a function of no arguments and returns the
result. Used to invoke side effects e.g.
(state-flow.core/invoke #(Thread/sleep 1000))"
[my-fn]
(error-catching-state (fn [s] [(my-fn) s])))
(defn when
"Given an expression `e` and a flow, if the expression is logical true, return the flow. Otherwise, return nil in a monadic context."
[e flow]
(if e
flow
(return nil)))
(def
^{:doc "Creates a flow that returns the application of f to the return of flow"
:arglists '([f flow])}
fmap
m/fmap)
(defn ^:deprecated swap
"DEPRECATED: use state-flow.state/modify instead."
[f]
(modify f))
(def ^{:deprecated true
:doc "DEPRECATED: Use state-flow.state/invoke instead."}
wrap-fn
invoke)
(def state? state/state?)
(def run state/run)
(def eval state/eval)
(def exec state/exec)
(defn ensure-step
"Internal use only.
Given a state-flow step, returns value as/is, else wraps value in a state-flow step."
[value]
(if (state? value)
value
(return value)))