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Roman numerals/Decode (view source)

Revision as of 13:30, 19 June 2024

480 bytes removed ,  17 days ago
m
→‎JS Folding from the right: Tidied
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Line 4,445:
(fold and foldr examples)
<syntaxhighlight lang="javascript">(() => {
"use strict";
 
// -------------- ROMAN NUMERALS DECODED ---------------
 
// Folding from right to left,
Line 4,454 ⟶ 4,455:
// fromRoman :: String -> Int
const fromRoman = s =>
foldr(l => ([r, n...s]) => [
l,.map(glyphValue)
l >= r ? .reduceRight(
([r, n], l) => n + l[
) : n - l,
])([0, 0])( l >= r
[...s].map(charVal) ? n + l
I : 1,n - l▼
a],▼
V: 5[0, 0]▼
)[1];
 
// charVal :: Char -> Maybe Int▼
const charVal = k => {
const v = {
▲ I: 1,
▲ V: 5,
X: 10,
L: 50,
C: 100,▼
D: 500,▼
M: 1000▼
} [k];
return v !== undefined ? v : 0;
};▼
 
▲ // charValglyphValue :: Char -> Maybe Int
// ----------------------- TEST ------------------------▼
const mainglyphValue = ()k => [({
);I: 1,▼
'MDCLXVI', 'MCMXC', 'MMVIII', 'MMXVI', 'MMXVII'▼
]V: 5,
.map(fromRoman)X: 10,
.join('\n');L: 50,
▲ C: 100,
▲ D: 500,
▲ M: 1000
▲ }) [k] || 0;
 
▲ // ----------------------- TEST ------------------------
 
return main();[▼
// ----------------- GENERIC FUNCTIONS -----------------
▲ '"MDCLXVI'", '"MCMXC'", '"MMVIII'", '"MMXVI'", '"MMXVII'"
 
▲ };]
// foldr :: (a -> b -> b) -> b -> [a] -> b
.map(fromRoman)
const foldr = f =>
.join("\n");
// Note that that the Haskell signature of foldr
// differs from that of foldl - the positions of
// accumulator and current value are reversed.
a => xs => [...xs].reduceRight(
(a, x) => f(x)(a),
▲ a
▲ );
 
// MAIN ---
▲ return main();
})();</syntaxhighlight>
{{Out}}
Hout
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