Use a gensym for it in anaphoric macros

This commit is contained in:
Kodi Arfer 2019-12-21 13:26:37 -05:00
parent bafd919605
commit e57bbb92db
3 changed files with 50 additions and 18 deletions

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@ -17,6 +17,12 @@ To use these macros you need to require the ``hy.extra.anaphoric`` module like s
``(require [hy.extra.anaphoric [*]])``
These macros are implemented by replacing any use of the designated
anaphoric symbols (``it``, in most cases) with a gensym. Consequently,
it's unwise to nest these macros, or to use an affected symbol as
something other than a variable name, as in ``(print "My favorite
Stephen King book is" 'it)``.
.. _ap-if:
ap-if

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@ -6,72 +6,72 @@
;;; These macros make writing functional programs more concise
(defmacro ap-if [test-form then-form &optional else-form]
`(do
(rit `(do
(setv it ~test-form)
(if it ~then-form ~else-form)))
(if it ~then-form ~else-form))))
(defmacro ap-each [lst &rest body]
"Evaluate the body form for each element in the list."
`(for [it ~lst] ~@body))
(rit `(for [it ~lst] ~@body)))
(defmacro ap-each-while [lst form &rest body]
"Evaluate the body form for each element in the list while the
predicate form evaluates to True."
`(for [it ~lst]
(rit `(for [it ~lst]
(unless ~form
(break))
~@body))
~@body)))
(defmacro ap-map [form lst]
"Yield elements evaluated in the form for each element in the list."
`(gfor it ~lst ~form))
(rit `(gfor it ~lst ~form)))
(defmacro ap-map-when [predfn rep lst]
"Yield elements evaluated for each element in the list when the
predicate function returns True."
`(gfor it ~lst (if (~predfn it) ~rep it)))
(rit `(gfor it ~lst (if (~predfn it) ~rep it))))
(defmacro ap-filter [form lst]
"Yield elements returned when the predicate form evaluates to True."
`(gfor it ~lst :if ~form it))
(rit `(gfor it ~lst :if ~form it)))
(defmacro ap-reject [form lst]
"Yield elements returned when the predicate form evaluates to False"
`(gfor it ~lst :if (not ~form) it))
(rit `(gfor it ~lst :if (not ~form) it)))
(defmacro ap-dotimes [n &rest body]
"Execute body for side effects `n' times, with it bound from 0 to n-1"
`(for [it (range ~n)]
~@body))
(rit `(for [it (range ~n)]
~@body)))
(defmacro ap-first [predfn lst]
"Yield the first element that passes `predfn`"
`(next
(rit `(next
(gfor it ~lst :if ~predfn it)
None))
None)))
(defmacro ap-last [predfn lst]
"Yield the last element that passes `predfn`"
(setv x (gensym))
`(do
(rit `(do
(setv ~x None)
(for [it ~lst :if ~predfn]
(setv ~x it))
~x))
~x)))
(defmacro! ap-reduce [form o!lst &optional [initial-value None]]
"Anaphoric form of reduce, `acc' and `it' can be used for a form"
`(do
(recur-sym-replace {'it (gensym) 'acc (gensym)} `(do
(setv acc ~(if (none? initial-value)
`(do
(setv ~g!lst (iter ~g!lst))
@ -79,7 +79,7 @@
initial-value))
(for [it ~g!lst]
(setv acc ~form))
acc))
acc)))
(deftag % [expr]
@ -111,3 +111,23 @@
'(&kwargs %**))]
~expr))
;;; --------------------------------------------------
;;; Subroutines
;;; --------------------------------------------------
(defn recur-sym-replace [d form]
"Recursive symbol replacement."
(cond
[(instance? HySymbol form)
(.get d form form)]
[(coll? form)
((type form) (gfor x form (recur-sym-replace d x)))]
[True
form]))
(defn rit [form]
"Replace `it` with a gensym throughout `form`."
(recur-sym-replace {'it (gensym)} form))

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@ -7,7 +7,13 @@
(defn test-ap-if []
(ap-if True (assert (is it True)))
(ap-if False True (assert (is it False))))
(ap-if False True (assert (is it False)))
; https://github.com/hylang/hy/issues/1847
(setv it "orig")
(setv out (ap-if (+ 1 1) (+ it 1) (+ it 10)))
(assert (= out 3))
(assert (= it "orig")))
(defn test-ap-each []
(setv res [])