Differences

This shows you the differences between two versions of the page.

--- codesnippets:bindingandpatternmatching [2021/04/14 10:43] – [Tuples] f2b216
+++ codesnippets:bindingandpatternmatching [2025/10/08 00:48] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
-====== Binding ======
+====== Binding and pattern matching ======
-~~DISCUSSION~~
 A binding binds a name or even several names with a function definition.
@@ Line 119: / Line 118: @@
 </code>
-==== Example 2 ====
+==== Algebraic data types ====
-<code Haskell>
+  * type definitions
-Person name number = Person "Lutz" 1243
+    * algebraic data types can be defined in the form ''data'' <TypeName> ''='' <DataConstructorA> <DataTypeA1> <DataTypeA2> ... <DataTypeAN> ''|'' <DataConstructorB> <DataTypeB1> <DataTypeB2> ... <DataTypeBM> ''|'' <DataConstructorO> ...
+    * whereas ''|'' devides variants simmilar to variants in unions in programming the language C and C++
+    * each variant has to have a constructor
+    * each constructor can contain zero, one or more data types
+  * construction of data of algebraic data types
+    * constructed in the form <DataConstructor> <Value1> <Value2> ... <ValueN>
+    * whereas the values have to conform with the data type declaration
+  * pattern maching with tuples
+    * in the same form as thay are constructed above
+    * but with binding names
+  * example
+    * code lines:<code Haskell>
+data MyData = MyVariantA Integer Char Double | MyVariantB Int | MyVariantC
+MyVariantA first b zet = MyVariantA 12 'a' 23.4
 </code>
+    * work in:<code Haskell>
-...works in...
-<code Haskell>
-module Main where
 main :: IO ()
 main =
-        do
+    do
-                print name
+        print first
-                print number
+        print b
+        print zet
-data Person = Person { sName :: String, iNumber :: Integer }
+data MyData = MyVariantA Integer Char Double | MyVariantB Int | MyVariantC
-Person name number = Person "Lutz" 1243
+MyVariantA first b zet = MyVariantA 12 'a' 23.4
+MyVariantB n = MyVariantB 123
+MyVariantC = MyVariantC -- is not binding anything, but compiles consistently
 </code>
+    * with compiler warning, which we ignore for pedagogical reasons
+    * executes, with output:<code>
+'a'
+.4
+</code>
+  * NOTE: I may look like: It does'nt make sense to have a constructor no elements. However, ''MyVariantC'' is already a value in itself, and can be used to differentiate between the variants.
+===== ✎ =====
+~~DISCUSSION~~