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--- background [2021/09/18 10:02] – [Understanding] f2b216
+++ background [2025/10/08 00:44] (current) – external edit 127.0.0.1
@@ Line 7: / Line 7: @@
 ====== Difficulties to understand Haskell? You are not alone. ======
-Learning Haskell was quite hard for me, and I needed to be confident that my own code really works under which conditions. This is may be the same for you.
+Learning Haskell was quite hard for me, and I needed to be confident that my own code really works, and under which conditions. This is may be the same for you.
 The reasons for the difficulties in learning Haskell, may be:
   * Before I started with Haskell, I was only used to imperative languages (Assembler, C, Pascal, Modula-2, C++, PHP, and more). The most, I was used to C++.
   * The difference between the imperative paradigm and the functional paradigm is like the difference between hockey and chess. It is both sport, isn't it? ;-)
-  * Often, the code examples in the are not appropriate.
+  * Often, the code examples are not appropriate.
     * ..or I am to stupid?
-    * A lot of the available examples are outdated.
+    * A lot of the available examples are outdated, and incompatible with current packages, libraries and compiler versions.
     * Often just incomplete.
-    * Often incompatible with the current packages.
     * Often they contain confusing useless, warning generating statements.
       * Example here: [[confusing:lyahpop|Confusing pop statement in LYAH]]
@@ Line 33: / Line 32: @@
 ===== Understanding Haskell =====
-Let's understand how Haskell works?
+Just to imagine how rich Haskell is in terms of abstraction - and to understand how must can be and sometimes has to be understood - enyoy the example below.
+The following shows how 10 primes are evaluated and displayed starting with the one millionth prime number.
   * Example )<sup>1</sup> )<sup>2</sup>:
@@ Line 56: / Line 57: @@
 </code>
-To understand this code (7 lines of code) completely I have to understand the following:
+To understand this code (8 lines of code) completely I have to understand the following:
   - Packets
   - Import
@@ Line 92: / Line 93: @@
 )<sup>1</sup> The code may __**not**__ work with extrem large numbers. I do not know at which conditions the floor function would fail. My calculator says sqrt((1E16x1E16)-1) is 9.999.999.999.999.999,9999999999999999, but sqrt((1E17x1E17)-1) is (1E17)!
+The following code (sieve of Erastothenes) will also work but by far not as fast for large numbers (approximately 100 times slower for the first 20 thousand prime numbers):
+<code Haskell>
+primes = let sieve (n0:lrn) = n0 : sieve [ n | n <- lrn, n `mod` n0 /= 0 ] in sieve [2..]
+</code>
 )<sup>2</sup> The code compiles without any warnings with ghc 8.10.4 and option -Wall.