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authorEuAndreh <eu@euandre.org>2023-04-08 16:20:00 -0300
committerEuAndreh <eu@euandre.org>2023-04-08 21:18:22 -0300
commit6c2cbb02ac4b16ee7b4c37de50403ce604868ec0 (patch)
treeffb2fb30a741a04f89474f64a2e01df3d891cd12 /v2/src/content/pt
parentv2: src/lib/: Unmark things as executable (diff)
downloadeuandre.org-6c2cbb02ac4b16ee7b4c37de50403ce604868ec0.tar.gz
euandre.org-6c2cbb02ac4b16ee7b4c37de50403ce604868ec0.tar.xz
v2: i18n of the collection name, "article" collection in root
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-rw-r--r--v2/src/content/pt/hea/condicional-ternario-lisp.md65
-rw-r--r--v2/src/content/pt/pastebin/exercicios-sicp-e-19.md (renamed from v2/src/content/pt/pastebins/exercicios-sicp-e-19.md)0
-rw-r--r--v2/src/content/pt/sobre.page (renamed from v2/src/content/pt/sobre.md)0
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diff --git a/v2/src/content/pt/hea/condicional-ternario-lisp.md b/v2/src/content/pt/hea/condicional-ternario-lisp.md
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+---
+
+title: Three-way conditional for number signs on Lisp
+
+date: 2021-04-24 3
+
+update: 2021-08-14
+
+categories: lisp scheme common-lisp
+
+---
+
+A useful macro from Paul Graham's [On Lisp][on-lisp] book:
+
+```lisp
+(defmacro nif (expr pos zero neg)
+ (let ((g (gensym)))
+ `(let ((,g ,expr))
+ (cond ((plusp ,g) ,pos)
+ ((zerop ,g) ,zero)
+ (t ,neg)))))
+```
+
+After I looked at this macro, I started seeing opportunities to using it in
+many places, and yet I didn't see anyone else using it.
+
+The latest example I can think of is section 1.3.3 of [Structure and
+Interpretation of Computer Programs][sicp], which I was reading recently:
+
+```scheme
+(define (search f neg-point pos-point)
+ (let ((midpoint (average neg-point pos-point)))
+ (if (close-enough? neg-point post-point)
+ midpoint
+ (let ((test-value (f midpoint)))
+ (cond ((positive? test-value)
+ (search f neg-point midpoint))
+ ((negative? test-value)
+ (search f midpoint pos-point))
+ (else midpoint))))))
+```
+
+Not that the book should introduce such macro this early, but I couldn't
+avoid feeling bothered by not using the `nif` macro, which could even remove
+the need for the intermediate `test-value` variable:
+
+```scheme
+(define (search f neg-point pos-point)
+ (let ((midpoint (average neg-point pos-point)))
+ (if (close-enough? neg-point post-point)
+ midpoint
+ (nif (f midpoint)
+ (search f neg-point midpoint)
+ (midpoint)
+ (search f midpoint pos-point)))))
+```
+
+It also avoids `cond`'s extra clunky parentheses for grouping, which is
+unnecessary but built-in.
+
+As a macro, I personally feel it tilts the balance towards expressivenes
+despite its extra cognitive load toll.
+
+[on-lisp]: http://www.paulgraham.com/onlisptext.html [sicp]:
+https://mitpress.mit.edu/sites/default/files/sicp/index.html
diff --git a/v2/src/content/pt/pastebins/exercicios-sicp-e-19.md b/v2/src/content/pt/pastebin/exercicios-sicp-e-19.md
index 89dacfd..89dacfd 100644
--- a/v2/src/content/pt/pastebins/exercicios-sicp-e-19.md
+++ b/v2/src/content/pt/pastebin/exercicios-sicp-e-19.md
diff --git a/v2/src/content/pt/sobre.md b/v2/src/content/pt/sobre.page
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--- a/v2/src/content/pt/sobre.md
+++ b/v2/src/content/pt/sobre.page