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Add docs and tests for as-> macro #1141

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Nov 3, 2016
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Add docs and tests for as-> macro #1141

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25843f5
Add docs and tests for as-> macro
tuturto Oct 25, 2016
5ab4649
Fix typo in as-> docstring
tuturto Oct 25, 2016
4411f10
Update docs based on review
tuturto Oct 25, 2016
3bf0184
Fix typo in as-> documentation
tuturto Oct 27, 2016
ffd28fa
Add better examples for as->
tuturto Oct 29, 2016
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52 changes: 52 additions & 0 deletions docs/language/api.rst
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Expand Up @@ -179,6 +179,58 @@ other case, the first false value will be returned. Example usage:
False


as->
----

.. versionadded:: 0.12.0

Expands to sequence of assignments to the provided name, starting with head.
The previous result is thus available in the subsequent form. Returns the final
result, and leaves the name bound to it in the local scope. This behaves much
like the other threading macros, but requires you to specify the threading
point per form via the name instead of always the first or last arument.
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...this is kind of confusing. I mean, I'm guessing that there will likely never be a "simple" explanation for something like this. I think maybe at minimum the example should use something more descriptive than x; maybe assigned_name?

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@tuturto tuturto Oct 25, 2016 •
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true, assigned-name is much better. I'll try to think better explanation, but currently I'm drawing a blank.

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@gilch gilch Oct 27, 2016 •
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I disagree that assigned-name is better. Perhaps you could use it in the first example just to point out which argument is which, but certainly not for all of them. The whole point of as-> is an alternative to -> and ->>, but where the insertion point can be anywhere in the list, instead of the first or last argument only. For deeply nested calls, this name may have to be repeated many times. Therefore, idiomatic usage is with a very short name, perhaps one or two letters. (This is not a problem for -> and ->> where the point is implied by the position.)

Perhaps the documentation would be clearer if you demonstrated how to accomplish a -> using as->. You can also look at Clojure's community documentation for clarification.

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Instead of assigned-name I could also us it as it's short and generic enough. I'll try to come up with a better examples still, that would highlight usage of as-> better (as now the example could be easily rewritten with ->).


.. code-block:: clj

;; create data for our cuttlefish database

=> (setv data [{:name "hooded cuttlefish"
... :classification {:subgenus "Acanthosepion"
... :species "Sepia prashadi"}
... :discovered {:year 1936
... :name "Ronald Winckworth"}}
... {:name "slender cuttlefish"
... :classification {:subgenus "Doratosepion"
... :species "Sepia braggi"}
... :discovered {:year 1907
... :name "Sir Joseph Cooke Verco"}}])

;; retrieve name of first entry
=> (as-> (first data) assigned-name
... (:name assigned-name))
'hooded cuttlefish'

;; retrieve species of first entry
=> (as-> (first data) assigned-name
... (:classification assigned-name)
... (:species assigned-name))
'Sepia prashadi'

;; find out who discovered slender cuttlefish
=> (as-> (filter (fn [entry] (= (:name entry)
... "slender cuttlefish")) data) assigned-name
... (first assigned-name)
... (:discovered assigned-name)
... (:name assigned-name))
'Sir Joseph Cooke Verco'

.. note::

In these examples, the REPL will report a tuple (e.g. `('Sepia prashadi',
'Sepia prashadi')`) as the result, but only a single value is actually
returned.


assert
------

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2 changes: 1 addition & 1 deletion hy/core/macros.hy
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Expand Up @@ -35,7 +35,7 @@
The previous result is thus available in the subsequent form. Returns the
final result, and leaves the name bound to it in the local scope. This behaves
much like the other threading macros, but requires you to specify the threading
point per form via the name instead of always the first or last arument."
point per form via the name instead of always the first or last argument."
`(do (setv
~name ~head
~@(interleave (repeat name) rest))
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23 changes: 23 additions & 0 deletions tests/native_tests/language.hy
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Expand Up @@ -588,6 +588,29 @@
["X" "B" "C" "D"])))


(defn test-as-threading []
"NATIVE: test as threading macro"
(setv data [{:name "hooded cuttlefish"
:classification {:subgenus "Acanthosepion"
:species "Sepia prashadi"}
:discovered {:year 1936
:name "Ronald Winckworth"}}
{:name "slender cuttlefish"
:classification {:subgenus "Doratosepion"
:species "Sepia braggi"}
:discovered {:year 1907
:name "Sir Joseph Cooke Verco"}}])
(assert (= (as-> (first data) x
(:name x))
"hooded cuttlefish"))
(assert (= (as-> (filter (fn [entry] (= (:name entry)
"slender cuttlefish")) data) x
(first x)
(:discovered x)
(:name x))
"Sir Joseph Cooke Verco")))


(defn test-assoc []
"NATIVE: test assoc"
(setv vals {"one" "two"})
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