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epsilon.cljc
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epsilon.cljc
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(ns meander.strategy.epsilon
"Rewrite strategy combinators.
A strategy is a unary function of a term (any object) and returns
the term rewritten.
Notation:
t ∈ Term
p, q, r, s ∈ Strategy"
(:refer-clojure :exclude [find while repeat some spread])
#?(:cljs (:require-macros [meander.strategy.epsilon]))
(:require
[clojure.core :as clj]
[clojure.set :as set]
[meander.match.epsilon :as r.match :include-macros true]
[meander.match.syntax.epsilon :as r.match.syntax :include-macros true]
[meander.protocols.epsilon :as r.protocols]
[meander.substitute.epsilon :as r.substitute :include-macros true]
[meander.syntax.epsilon :as r.syntax :include-macros true]))
(def
^{:arglists '([t])
:dynamic true}
*pass*
"Strategy which returns t."
(reify
#?@(:clj [clojure.lang.IFn
(invoke [_ t] t)
(applyTo [_ args] (first args))]
:cljs [cljs.core/IFn
(-invoke [_ t] t)
;; TODO: why no applyTo?
#_(-applyTo [_ args] (first args))])))
#?(:clj
(defmethod print-method (class *pass*) [v ^java.io.Writer w]
(.write w "#meander.epsilon/pass[]"))
:cljs
(specify! *pass* IPrintWithWriter
(-pr-writer [new-obj writer _]
(write-all writer "#meander.epsilon/pass[]"))))
(defn pass?
"true if `x` is `*pass*`, false otherwise."
[x]
(identical? x *pass*))
(defn pass
"Strategy which returns t."
[t]
(*pass* t))
(def
^{:arglists '([t])
:dynamic true}
*fail*
"Strategy which always fails."
(reify
#?@(:clj [clojure.lang.IFn
(invoke [this _] this)
(applyTo [this _] this)]
:cljs [cljs.core/IFn
(-invoke [this _] this)
;; TODO: why no applyTo?
#_(-applyTo [this _] this)])))
#?(:clj
(defmethod print-method (class *fail*) [v ^java.io.Writer w]
(.write w "#meander.epsilon/fail[]"))
:cljs
(specify! *fail* IPrintWithWriter
(-pr-writer [new-obj writer _]
(write-all writer "#meander.epsilon/fail[]"))))
(defn fail?
"true if `x` is `*fail*`, false otherwise."
[x]
(identical? x *fail*))
(defn fail
"Strategy which always fails."
[t]
(*fail* t))
(defn build
"Build a strategy which always returns `t`."
[t]
(fn [_] t))
(defmacro pipe-body
{:private true}
([params]
(let [t (gensym "t__")]
`(if (or ~@(map (partial list `fail?) params))
*fail*
(fn [~t]
~(reduce
(fn [inner-form p]
`(let [~t (~p ~t)]
(if (fail? ~t)
*fail*
~inner-form)))
t
(reverse params)))))))
(defn pipe
"Build a strategy which applies `p` to `t` and then `q` iff `p` rewrites
`t`. If `p` and `q` are successful, return the result, otherwise
return `*fail*`."
{:arglists '([] [p] [p q] [p q & more])}
([] *pass*)
([p] p)
([p q]
(meander.strategy.epsilon/pipe-body [p q]))
([p q r]
(meander.strategy.epsilon/pipe-body [p q r]))
([p q r s]
(meander.strategy.epsilon/pipe-body [p q r s]))
([p q r s & more]
(apply pipe (meander.strategy.epsilon/pipe-body [p q r s]) more)))
(defmacro choice-body
{:private true}
[params]
(let [t (gensym "t__")
t* (gensym "t__")]
`(fn [~t]
~(reduce
(fn [inner-form p]
`(let [~t* (~p ~t)]
(if (fail? ~t*)
~inner-form
~t*)))
`*fail*
(reverse params)))))
(defn choice
"Build a strategy which applies `p` or `q` to `t`. If `p` rewrites,
return the result, otherwise apply `q`."
{:arglists '([] [p] [p q] [p q & more])}
([] *fail*)
([p] p)
([p q]
(meander.strategy.epsilon/choice-body [p q]))
([p q r]
(meander.strategy.epsilon/choice-body [p q r]))
([p q r s]
(meander.strategy.epsilon/choice-body [p q r s]))
([p q r s & more]
(apply choice (meander.strategy.epsilon/choice-body [p q r s]) more)))
(defn branch
{:style/indent :defn}
[p q r]
(fn [t]
(let [t* (p t)]
(if (fail? t*)
(r t)
(q t*)))))
(defn attempt
"Build a strategy which attempts apply `s` to a term. If `s`
succeeds, it returns the result. If `s` fails return the original
term."
[s]
(choice s *pass*))
(defn pred
"Build a strategy which returns `t` iff `p` is true for `t` and
fails otherwise."
[p]
(fn [t]
(if (p t)
t
*fail*)))
(defn guard
"Build a strategy which applies `s` to `t` iff `p` is true for `t`."
{:style/indent :defn}
[p s]
(attempt (pipe (pred p) s)))
(defn repeat
"Build a strategy which applies `s` to `t` repeatedly until failure.
Note that, if used in conjunction with a strategy which never fails
i.e. `attempt`, this will cause a stack overflow. To avoid this, use
`while` or `until`.
Example:
((repeat
(pipe (pred vector?)
(fn [v]
(if (seq v)
(if (= (peek v) 2)
*fail*
(pop v))
*fail*))))
[1 2 3 4])
;; =>
[1 2]
"
[s]
(fn rec [t]
((attempt (pipe s rec)) t)))
(defn while
"Build a strategy which repeatedly applies `s` to `t` so long as `pred`
is false for `t` and `t*`.
((while not=
(rewrite
('let [!bs !vs ... ?b ?v]
. !body ...)
('let [!bs !vs ...]
(('fn [?b]
. !body ...)
?v))
('let [] ?x)
?x))
'(let [a 1
b 2
c 3]
(+ a b c)))
;; =>
((fn [a] ((fn [b] ((fn [c] (+ a b c)) 3)) 2)) 1)
"
{:style/indent :defn}
[pred s]
(fn rec [t]
((pipe (attempt s)
(fn [t*]
(if (pred t t*)
(rec t*)
t*)))
t)))
(defn until
"Build a strategy which repeatedly applies `s` to `t` so long as `pred`
is false for `t` and `t*`.
((until =
(rewrite
('let [!bs !vs ... ?b ?v]
. !body ...)
('let [!bs !vs ...]
(('fn [?b]
. !body ...)
?v))
('let [] ?x)
?x))
'(let [a 1
b 2
c 3]
(+ a b c)))
;; =>
((fn [a] ((fn [b] ((fn [c] (+ a b c)) 3)) 2)) 1)"
{:style/indent :defn}
[pred s]
(fn [t]
(let [t* ((attempt s) t)]
(if (pred t t*)
t*
(recur t*)))))
(defn n-times
"Builds a strategy that repeats the passed in strategy `n` times.
This is particularly useful for non-terminating rewrites or
when you are trying to write a strategy and want to make sure you
don't accidentally infinite loop.
((n-times 2
(rewrite
?x (?x ?x)))
:x)
;; => ((:x :x) (:x :x))
"
{:style/indent :defn}
[n s]
(apply pipe (clojure.core/repeat n s)))
(defn fix
"Return a strategy which applies the strategy `s` to a term `t`
repeatedly until it the result of applying `s` its argument returns
its argument.
(def to-pair
(fix (rewrite
[?x ?y]
[?x ?y]
?x
[?x ?x])))
(to-pair [1 2])
;; => [1 2]
(to-pair 1)
;; => [1 1]"
[s]
(fn [t]
(let [t* (s t)]
(if (= t* t)
t
(recur t*)))))
;; ---------------------------------------------------------------------
;; IAll implementation
(defn iall? [x]
(satisfies? r.protocols/IAll x))
(defmacro iseq-all-body
[t s]
`(let [res# (reduce
(fn [t*# x#]
(let [x*# (~s x#)]
(if (fail? x*#)
(reduced *fail*)
(concat t*# (list x*#)))))
()
~t)]
(if (fail? res#)
res#
(vary-meta res# (fn [new-meta#] (merge (meta ~t) new-meta#))))))
(defmacro ivector-all-body
{:private true}
[t s]
`(reduce
(fn [t*# x#]
(let [x*# (~s x#)]
(if (fail? x*#)
(reduced *fail*)
(conj t*# x*#))))
(empty ~t)
~t))
(defmacro imap-all-body
{:private true}
[t s]
`(reduce-kv
(fn [t*# k# v#]
(let [k*# (~s k#)]
(if (fail? k*#)
*fail*
(let [v*# (~s v#)]
(if (fail? v*#)
*fail*
(assoc t*# k*# v*#))))))
(empty ~t)
~t))
(defmacro irecord-all-body
{:private true}
[t s]
`(reduce-kv
(fn [t*# k# v#]
(let [k*# (~s k#)]
(if (fail? k*#)
*fail*
(let [v*# (~s v#)]
(if (fail? v*#)
*fail*
(assoc t*# k*# v*#))))))
~t
~t))
(defmacro iset-all-body
{:private true}
[t s]
`(reduce
(fn [t*# x#]
(let [x*# (~s x#)]
(if (fail? x*#)
(reduced *fail*)
(conj t*# x*#))))
(empty ~t)
~t))
(extend-protocol r.protocols/IAll
#?@(:clj [clojure.lang.IPersistentMap (-all [this s] (imap-all-body this s))])
#?@(:clj [clojure.lang.IPersistentSet (-all [this s] (iset-all-body this s))])
#?@(:clj [clojure.lang.IPersistentVector (-all [this s] (ivector-all-body this s))])
#?@(:clj [clojure.lang.ISeq (-all [this s] (iseq-all-body this s))])
#?@(:cljs [cljs.core/LazySeq (-all [this s] (meander.strategy.epsilon/iseq-all-body this s))])
#?@(:cljs [cljs.core/List (-all [this s] (meander.strategy.epsilon/iseq-all-body this s))])
#?@(:cljs [cljs.core/PersistentArrayMap (-all [this s] (meander.strategy.epsilon/imap-all-body this s))])
#?@(:cljs [cljs.core/PersistentHashMap (-all [this s] (meander.strategy.epsilon/imap-all-body this s))])
#?@(:cljs [cljs.core/PersistentHashSet (-all [this s] (meander.strategy.epsilon/iset-all-body this s))])
#?@(:cljs [cljs.core/PersistentVector (-all [this s] (meander.strategy.epsilon/ivector-all-body this s))])
#?@(:cljs [cljs.core/Range (-all [this s] (meander.strategy.epsilon/iseq-all-body this s))]))
(defn all [s]
#?(:clj
(fn [t]
(cond
(record? t) (irecord-all-body t s)
(iall? t) (r.protocols/-all t s)
:else t))
:cljs
(fn [t]
(cond
(iall? t)
(r.protocols/-all t s)
(satisfies? cljs.core/IRecord t)
(meander.strategy.epsilon/irecord-all-body t s)
(satisfies? cljs.core/ISeq t)
(meander.strategy.epsilon/iseq-all-body t s)
(satisfies? cljs.core/IVector t)
(meander.strategy.epsilon/ivector-all-body t s)
(satisfies? cljs.core/IMap t)
(meander.strategy.epsilon/iseq-all-body t s)
(satisfies? cljs.core/ISet t)
(meander.strategy.epsilon/iseq-all-body t s)
:else
t))))
(defn all-td
"Apply the all strategy with `s` to every subterm in `t` from the
top down."
[s]
(fn rec [t]
((choice s (all rec)) t)))
(defn all-bu
"Apply the all strategy with `s` to every subterm in `t` from the
bottom up."
[s]
(fn rec [t]
((choice (all rec) s) t)))
;; ---------------------------------------------------------------------
;; IOne implementation
(defn ione? [x]
(satisfies? r.protocols/IOne x))
(defmacro iseq-one-body
{:private true}
[t s]
`(reduce
(fn [_acc# [i# x#]]
(let [x*# (~s x#)]
(if (fail? x*#)
*fail*
(reduced (concat (take i# ~t)
(list x*#)
(drop (inc i#) ~t))))))
*fail*
(map-indexed vector ~t)))
(defmacro ivector-one-body
{:private true}
[t s]
`(reduce-kv
(fn [acc# i# x#]
(let [x*# (~s x#)]
(if (fail? x*#)
acc#
(reduced (assoc ~t i# x*#)))))
*fail*
~t))
(defmacro imap-one-body
{:private true}
[t s]
`(reduce-kv
(fn [acc# k# v#]
(let [k*# (~s k#)]
(if (fail? k*#)
(let [v*# (~s v#)]
(if (fail? v*#)
acc#
(reduced (assoc ~t k# v*#))))
(reduced (assoc ~t k*# v#)))))
*fail*
~t))
(defmacro iset-one-body
{:private true}
[t s]
`(reduce
(fn [acc# x#]
(let [x*# (~s x#)]
(if (fail? x*#)
*fail*
(reduced (conj (disj ~t x#) x*#)))))
*fail*
~t))
(extend-protocol r.protocols/IOne
#?@(:clj [clojure.lang.IPersistentMap (-one [this s] (imap-one-body this s))])
#?@(:clj [clojure.lang.IPersistentSet (-one [this s] (iset-one-body this s))])
#?@(:clj [clojure.lang.IPersistentVector (-one [this s] (ivector-one-body this s))])
#?@(:clj [clojure.lang.ISeq (-one [this s] (iseq-one-body this s))])
#?@(:cljs [cljs.core/LazySeq (-one [this s] (meander.strategy.epsilon/iseq-one-body this s))])
#?@(:cljs [cljs.core/List (-one [this s] (meander.strategy.epsilon/iseq-one-body this s))])
#?@(:cljs [cljs.core/PersistentArrayMap (-one [this s] (meander.strategy.epsilon/imap-one-body this s))])
#?@(:cljs [cljs.core/PersistentHashMap (-one [this s] (meander.strategy.epsilon/imap-one-body this s))])
#?@(:cljs [cljs.core/PersistentHashSet (-one [this s] (meander.strategy.epsilon/iset-one-body this s))])
#?@(:cljs [cljs.core/PersistentVector (-one [this s] (meander.strategy.epsilon/ivector-one-body this s))])
#?@(:cljs [cljs.core/Range (-one [this s] (meander.strategy.epsilon/iseq-one-body this s))]))
(defn one [s]
#?(:clj
(fn [t]
(if (ione? t)
(r.protocols/-one t s)
t))
:cljs
(fn [t]
(cond
(ione? t)
(r.protocols/-one t s)
(satisfies? cljs.core/ISeq t)
(meander.strategy.epsilon/iseq-one-body t s)
(satisfies? cljs.core/IVector t)
(meander.strategy.epsilon/ivector-one-body t s)
(satisfies? cljs.core/IMap t)
(meander.strategy.epsilon/imap-one-body t s)
(satisfies? cljs.core/ISet t)
(meander.strategy.epsilon/iset-one-body t s)
:else
t))))
(defn once-td
"Apply the `one` strategy with `s` to every subterm in `t` from the
top down."
[s]
(fn rec [t]
((choice s (one rec)) t)))
(defn once-bu
"Apply the `one` strategy with `s` to every subterm in `t` from the
bottom up."
[s]
(fn rec [t]
((choice (one rec) s) t)))
;; ---------------------------------------------------------------------
;; ISome implementation
(defn isome? [x]
(satisfies? r.protocols/ISome x))
(defmacro iseq-some-body
{:private true}
[t s]
`(let [[t*# pass?#]
(reduce
(fn [[t*# pass?#] x#]
(let [x*# (~s x#)]
(if (fail? x*#)
[(cons x# t*#) pass?#]
[(cons x*# t*#) true])))
[() false]
(reverse ~t))]
(if pass?#
t*#
*fail*)))
(defmacro ivector-some-body
{:private true}
[t s]
`(let [[t*# pass?#]
(reduce-kv
(fn [[t*# pass?#] i# x#]
(let [x*# (~s x#)]
(if (fail? x*#)
[t*# pass?#]
[(assoc t*# i# x*#) true])))
[~t false]
~t)]
(if pass?#
t*#
*fail*)))
(defmacro imap-some-body
{:private true}
[t s]
`(let [[t*# pass?#]
(reduce-kv
(fn [[t*# pass?#] k# v#]
(let [k*# (~s k#)
v*# (~s v#)]
(case [(fail? k*#) (fail? v*#)]
[true true]
[(assoc t*# k# v#) pass?#]
[true false]
[(assoc t*# k# v*#) true]
[false true]
[(assoc t*# k*# v#) true]
[false false]
[(assoc t*# k*# v*#) true])))
[{} false]
~t)]
(if pass?#
t*#
*fail*)))
(defmacro irecord-some-body
{:private true}
[t s]
`(let [[t*# pass?#]
(reduce-kv
(fn [[t*# pass?#] k# v#]
(let [k*# (~s k#)
v*# (~s v#)]
(case [(fail? k*#) (fail? v*#)]
[true true]
[(assoc t*# k# v#) pass?#]
[true false]
[(assoc t*# k# v*#) true]
[false true]
[(assoc t*# k*# v#) true]
[false false]
[(assoc t*# k*# v*#) true])))
[~t false]
~t)]
(if pass?#
t*#
*fail*)))
(defmacro iset-some-body
{:private true}
[t s]
`(let [[t*# pass?#]
(reduce
(fn [[t*# pass?#] x#]
(let [x*# (~s x#)]
(if (fail? x*#)
[(conj t*# x#) pass?#]
[(conj t*# x*#) true])))
[#{} false]
~t)]
(if pass?#
t*#
*fail*)))
(extend-protocol r.protocols/ISome
#?@(:clj [clojure.lang.IPersistentMap (-some [this s] (imap-some-body this s))])
#?@(:clj [clojure.lang.IPersistentSet (-some [this s] (iset-some-body this s))])
#?@(:clj [clojure.lang.IPersistentVector (-some [this s] (ivector-some-body this s))])
#?@(:clj [clojure.lang.ISeq (-some [this s] (iseq-some-body this s))])
#?@(:cljs [cljs.core/LazySeq (-some [this s] (meander.strategy.epsilon/iseq-some-body this s))])
#?@(:cljs [cljs.core/List (-some [this s] (meander.strategy.epsilon/iseq-some-body this s))])
#?@(:cljs [cljs.core/PersistentArrayMap (-some [this s] (meander.strategy.epsilon/imap-some-body this s))])
#?@(:cljs [cljs.core/PersistentHashMap (-some [this s] (meander.strategy.epsilon/imap-some-body this s))])
#?@(:cljs [cljs.core/PersistentHashSet (-some [this s] (meander.strategy.epsilon/iset-some-body this s))])
#?@(:cljs [cljs.core/PersistentVector (-some [this s] (meander.strategy.epsilon/ivector-some-body this s))])
#?@(:cljs [cljs.core/Range (-some [this s] (meander.strategy.epsilon/iseq-some-body this s))]))
(defn some
"Build a strategy which applies `s` to as many direct subterms of
`t` as possible. Succeeds if at least one application applies, fails
otherwise."
[s]
#?(:clj
(fn [t]
(cond
(record? t)
(irecord-some-body t s)
(isome? t)
(r.protocols/-some t s)
:else t))
:cljs
(fn [t]
(cond
(isome? t)
(r.protocols/-some t s)
(satisfies? cljs.core/IRecord t)
(meander.strategy.epsilon/irecord-some-body t s)
(satisfies? cljs.core/ISeq t)
(meander.strategy.epsilon/iseq-some-body t s)
(satisfies? cljs.core/IVector t)
(meander.strategy.epsilon/ivector-some-body t s)
(satisfies? cljs.core/IMap t)
(meander.strategy.epsilon/imap-some-body t s)
(satisfies? cljs.core/ISet t)
(meander.strategy.epsilon/iset-some-body t s)
:else
t))))
(defn some-td
"Return a strategy which attempts to apply the strategy `s` to all
subterms of a term `t` from the top-down (pre-order). Succeeds if at
least one subterm of `t` passed to `s` succeeds, fails otherwise.
(def inc-numbers
(some-td (pipe (pred number?) inc)))
(inc-numbers [1 [\"2\" 3] \"4\"])
;;=> [2 [\"2\" 4] \"4\"]
(inc-numbers [\"1\" \"2\"])
;; => #meander.epsilon/fail[]"
[s]
(fn rec [t]
(if (isome? t)
((choice s (some rec)) t)
(s t))))
(defn some-bu
"Return a strategy which attempts to apply the strategy `s` to all
subterms of a term `t` from the bottom-up (post-order). Succeeds if
at least one subterm of `t` passed to `s` succeeds, fails otherwise.
(def inc-numbers
(some-td (pipe (pred number?) inc)))
(inc-numbers [1 [\"2\" 3] \"4\"])
;;=> [2 [\"2\" 4] \"4\"]
(inc-numbers [\"1\" \"2\"])
;; => #meander.epsilon/fail[]"
[s]
(fn rec [t]
(if (isome? t)
((choice (some rec) s) t)
(s t))))
;; ---------------------------------------------------------------------
;; IRetain implementation
(defn iretain? [x]
(satisfies? r.protocols/IRetain x))
(defmacro iseq-retain-body
{:private true}
[t s]
`(sequence (comp (map ~s) (remove fail?)) ~t))
(defmacro ivector-retain-body
{:private true}
[t s]
`(into [] (comp (map ~s) (remove fail?)) ~t))
(defmacro iset-retain-body
{:private true}
[t s]
`(into #{} (comp (map ~s) (remove fail?)) ~t))
(defmacro imap-retain-body
{:private true}
[t s]
`(into {} (comp (map ~s) (remove fail?)) ~t))
(extend-protocol r.protocols/IRetain
#?@(:clj [clojure.lang.IPersistentMap (-retain [this s] (imap-retain-body this s))])
#?@(:clj [clojure.lang.IPersistentSet (-retain [this s] (iset-retain-body this s))])
#?@(:clj [clojure.lang.IPersistentVector (-retain [this s] (ivector-retain-body this s))])
#?@(:clj [clojure.lang.ISeq (-retain [this s] (iseq-retain-body this s))])
#?@(:cljs [cljs.core/LazySeq (-retain [this s] (meander.strategy.epsilon/iseq-retain-body this s))])
#?@(:cljs [cljs.core/List (-retain [this s] (meander.strategy.epsilon/iseq-retain-body this s))])
#?@(:cljs [cljs.core/PersistentArrayMap (-retain [this s] (meander.strategy.epsilon/imap-retain-body this s))])
#?@(:cljs [cljs.core/PersistentHashMap (-retain [this s] (meander.strategy.epsilon/imap-retain-body this s))])
#?@(:cljs [cljs.core/PersistentHashSet (-retain [this s] (meander.strategy.epsilon/iset-retain-body this s))])
#?@(:cljs [cljs.core/PersistentVector (-retain [this s] (meander.strategy.epsilon/ivector-retain-body this s))])
#?@(:cljs [cljs.core/Range (-retain [this s] (meander.strategy.epsilon/iseq-retain-body this s))]))
(defn retain
"Return a strategy which retains subterms of t for which the
strategy s succeeds."
([s]
(fn [t]
#?(:clj
(if (iretain? t)
(r.protocols/-retain t s)
t)
:cljs
(cond
(iretain? t)
(r.protocols/-retain t s)
(satisfies? cljs.core/ISeq t)
(meander.strategy.epsilon/iseq-retain-body t s)
(satisfies? cljs.core/IVector t)
(meander.strategy.epsilon/ivector-retain-body t s)
(satisfies? cljs.core/IMap t)
(meander.strategy.epsilon/imap-retain-body t s)
(satisfies? cljs.core/ISet t)
(meander.strategy.epsilon/iset-retain-body t s)
:else
t))))
([s t]
#?(:clj
(if (iretain? t)
(r.protocols/-retain t s)
t)
:cljs
(cond
(iretain? t)
(r.protocols/-retain t s)
(satisfies? cljs.core/ISeq t)
(meander.strategy.epsilon/iseq-retain-body t s)
(satisfies? cljs.core/IVector t)
(meander.strategy.epsilon/ivector-retain-body t s)
(satisfies? cljs.core/IMap t)
(meander.strategy.epsilon/imap-retain-body t s)
(satisfies? cljs.core/ISet t)
(meander.strategy.epsilon/iset-retain-body t s)
:else
t))))
(defn spine-td
[s]
(fn rec [t]
((pipe s (attempt (one rec))) t)))
(defn spine-bu
[s]
(fn rec [t]
((pipe (attempt (one rec)) s) t)))
(defn breadth-first
"Build a strategy which applies `s` to each subterm of `t` in a
breadth-first order."
[s]
(fn rec [t]
((pipe (all s) (all rec)) t)))
(defn bottom-up
"Build a strategy which applies `s` to each subterm of `t` from
bottom to top."
[s]
(fn rec [t]
((pipe (all rec) s) t)))
(defn top-down
"Build a strategy which applies `s` to each subterm of `t` from
top to bottom."
[s]
(fn rec [t]
((pipe s (all rec)) t)))
(defn top-down-while
"Build a strategy which applies `s` to each subterm of `t` from
top to bottom so long as `pred` is true for some subterm of `t`."
[pred s]
(fn rec [t]
(if (pred t)
((pipe s (all rec)) t)
t)))
(defn top-down-until
"Build a strategy which applies `s` to each subterm of `t` from
top to bottom until `pred` is false for some subterm of `t`."
[pred s]
(fn rec [t]
(if (pred t)
t
((pipe s (all rec)) t))))
(defn outermost
"Build a strategy which repeatedly applies `s` to `t` starting from
the outermost subterm in `t` until it fails."
[s]
(repeat (once-td s)))
(defn innermost
"Build a strategy which repeatedly applies `s` to `t` starting from
the innermost subterm in `t`."
[s]
(fn rec [t]
((bottom-up (repeat s)) t)))
(defn trace
"Build a strategy which monitors the entry and exit values of `s`."
([s]
(trace s prn))
([s f]
(let [id (gensym "t_")]
(fn [t]
(f {:id id, :in t})
(let [t* (s t)]
(f {:id id, :out t*})
t*)))))
(defn spread
"Build a strategy which applies the first `n` values of `t` to `f`
iff `t` is a coll. Behaves like apply if `n` is not supplied. Useful
in conjunction with `juxt`.
((pipe
(tuple (comp (some keyword) keys)
vals)
(spread zipmap 2))
{\"foo\" \"bar\"
\"baz\" \"quux\"})
;; =>
{:foo \"bar\"
:baz \"quux\"}"
([f]
(fn spread-all [t]