@@ -1,27 +1,22 @@
1−## Pattern Matching
1+Pattern Matching
3Pattern matching deconstructs a value to bring zero or more expressions into scope. Pattern matches are introduced with the `case` keyword.
4Pattern matching deconstructs a value to bring zero or more expressions into scope. Pattern matches are introduced with the `case` keyword.
5−Pattern matches have the following general form
6+Pattern matches have the following general form::
8−case value of
8+ case value of
9− pattern -> result
9+ pattern -> result
11− pattern -> result
11+ pattern -> result
14−Pattern matching can also be used in the declaration of functions, as we have already seen:
13+Pattern matching can also be used in the declaration of functions, as we have already seen::
17−fn pattern_1 ... pattern_n = result
15+ fn pattern_1 ... pattern_n = result
20−Any of the above types of pattern are also valid when introducing functions. In addition, patterns can also be grouped in parentheses to introduce multiple-arugument functions. For example,
17+Any of the above types of pattern are also valid when introducing functions. In addition, patterns can also be grouped in parentheses to introduce multiple-arugument functions. For example::
23−example x (y, z) w = x * y + z * w
19+ example x (y, z) w = x * y + z * w
26The following pattern types are supported:
21The following pattern types are supported:
@@ -36,126 +31,109 @@ The following pattern types are supported:
37Patterns need not be exhaustive. A pattern match failed exception will be thrown at runtime if no pattern matches the input.
32Patterns need not be exhaustive. A pattern match failed exception will be thrown at runtime if no pattern matches the input.
39−## Wildcard Patterns
34+Wildcard Patterns
41−The wilcard `_` matches any input and brings nothing into scope:
37+The wilcard `_` matches any input and brings nothing into scope::
44−case x of
39+ case x of
48−## Literal Patterns
42+Literal Patterns
50−Literal patterns are provided to match on primitives:
45+Literal patterns are provided to match on primitives::
53−case booleanValue of
47+ case booleanValue of
54− true -> 0
48+ true -> 0
55− false -> 1
49+ false -> 1
57−case stringValue of
51+ case stringValue of
58− "Foo" -> 0
52+ "Foo" -> 0
61−case numericValue of
55+ case numericValue of
66−## Variable Pattern
59+Variable Patterns
68−A variable pattern matches any input and binds that input to its name:
62+A variable pattern matches any input and binds that input to its name::
71−case foo(x) of
64+ case foo(x) of
72− result -> bar(result)
65+ result -> bar(result)
75−## Array Patterns
67+Array Patterns
77−Array patterns match an input which is an array, and bring its elements into scope.
70+Array patterns match an input which is an array, and bring its elements into scope. For example::
82−f = \arr -> case arr of
72+ f = \arr -> case arr of
84− [x, y] -> x * y + f xs
74+ [x, y] -> x * y + f xs
88Here, the first pattern only matches arrays of length one, and brings the first element of the array into scope.
77Here, the first pattern only matches arrays of length one, and brings the first element of the array into scope.
90The second pattern matches arrays with two elements, and brings the first and second elements into scope.
79The second pattern matches arrays with two elements, and brings the first and second elements into scope.
92−## Cons Patterns
81+Cons Patterns
94−The head and tail of a non-empty array can be matched by using a cons pattern:
96−```haskell
84+The head and tail of a non-empty array can be matched by using a cons pattern::
97−add = \arr -> case arr of
102−`:` associates to the right:
86+ add = \arr -> case arr of
104−```haskell
90+`:` associates to the right::
105−addPairs = \arr -> case arr of
106− x : y : xs -> x * y + addPairs xs
110−## Record Patterns
92+ addPairs = \arr -> case arr of
93+ x : y : xs -> x * y + addPairs xs
112−Record patterns match an input which is a record, and bring its properties into scope.
96+Record Patterns
114−```haskell
99+Record patterns match an input which is a record, and bring its properties into scope::
116− { foo = "Foo" } -> o.bar
120−## Nested Patterns
101+ f = \o -> case o of
102+ { foo = "Foo" } -> o.bar
122−The patterns above can be combined to create larger patterns.
105+Nested Patterns
124−For example:
108+The patterns above can be combined to create larger patterns. For example::
127−f = \o -> case o of
110+ f = \o -> case o of
128− { arr = x : _, take = "car" } -> x
111+ { arr = x : _, take = "car" } -> x
129− { arr = _ : x : _, take = "cadr" } -> x
112+ { arr = _ : x : _, take = "cadr" } -> x
133−## Named Patterns
115+Named Patterns
135−Named patterns bring additional names into scope when using nested patterns. Any pattern can be named by using the `@` symbol:
118+Named patterns bring additional names into scope when using nested patterns. Any pattern can be named by using the `@` symbol::
138−f = \arr -> case arr of
120+ f = \arr -> case arr of
139− a@(_ : _ : _) -> true
121+ a@(_ : _ : _) -> true
140− a -> false
122+ a -> false
143Here, in the first pattern, any array with two or more elements will be matched and bound to the variable `a`.
124Here, in the first pattern, any array with two or more elements will be matched and bound to the variable `a`.
147−Guards are used to impose additional constraints inside a pattern using boolean-valued expressions, and are introduced with a pipe after the pattern:
129+Guards are used to impose additional constraints inside a pattern using boolean-valued expressions, and are introduced with a pipe after the pattern::
150−evens = \arr -> case arr of
131+ evens = \arr -> case arr of
152− x : xs | x % 2 == 0 -> 1 + evens xs
133+ x : xs | x % 2 == 0 -> 1 + evens xs
153− _ : xs -> evens xs
134+ _ : xs -> evens xs
156−When defining a function, guards appear after all patterns:
136+When using patterns to define a function at the top level, guards appear after all patterns::
159−greater x y | x > y = true
138+ greater x y | x > y = true
160−greater _ _ = false
139+ greater _ _ = false