1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
|
---
language: purescript
contributors:
- ["Fredrik Dyrkell", "http://www.lexicallyscoped.com"]
---
PureScript is a small strongly, statically typed language compiling to Javascript.
* Learn more at [http://www.purescript.org/](http://www.purescript.org/)
* Documentation: [http://docs.purescript.org/en/latest/](http://docs.purescript.org/en/latest/)
* Book: Purescript by Example, [https://leanpub.com/purescript/](https://leanpub.com/purescript/)
```haskell
--
-- 1. Primitive datatypes that corresponds to their Javascript
-- equivalents at runtime.
-- Numbers
1 + 7*5 :: Number -- 36
-- Types are inferred, so the following works fine
9 / 2.5 + 4.4 -- 8
-- Hexadecimal literals
0xff + 1 -- 256
-- Unary negation
6 * -3 -- -18
6 * negate 3 -- -18
-- Modulus
3 % 2 -- 1
4 % 2 -- 0
-- Inspect the type of an expression in psci
:t 9 / 2.5 + 4.4 -- Prim.Number
-- Booleans
true :: Boolean -- true
false :: Boolean -- false
-- Negation
not true --false
23 == 23 -- true
1 /= 4 -- true
1 >= 4 -- false
-- Comparisions < <= > >=
-- are defined in terms of compare
compare 1 2 -- LT
compare 2 2 -- EQ
compare 3 2 -- GT
-- Conjunction and Disjunction
true && (9 >= 19 || 1 < 2) -- true
-- Strings
"Hellow" :: String -- "Hellow"
-- Multiline string
"Hellow\
\orld" -- "Helloworld"
-- Concatenate
"such " ++ "amaze" -- "such amaze"
--
-- 2. Arrays are Javascript arrays, but must be homogeneous
[1,1,2,3,5,8] :: [Number] -- [1,1,2,3,5,8]
[true, true, false] :: [Boolean] -- [true,true,false]
-- [1,2, true, "false"] won't work
-- `Cannot unify Prim.Number with Prim.Boolean`
-- Cons (prepend)
1 : [2,4,3] -- [1,2,4,3]
-- Requires purescript-arrays (Data.Array)
-- and purescript-maybe (Data.Maybe)
-- Safe access return Maybe a
head [1,2,3] -- Just (1)
tail [3,2,1] -- Just ([2,1])
init [1,2,3] -- Just ([1,2])
last [3,2,1] -- Just (1)
-- Random access - indexing
[3,4,5,6,7] !! 2 -- Just (5)
-- Range
1..5 -- [1,2,3,4,5]
length [2,2,2] -- 3
drop 3 [5,4,3,2,1] -- [2,1]
take 3 [5,4,3,2,1] -- [5,4,3]
append [1,2,3] [4,5,6] -- [1,2,3,4,5,6]
--
-- 3. Records are Javascript objects, with zero or more fields, which
-- can have different types
let book = {title: "Foucault's pendulum", author: "Umberto Eco"}
-- Access properties
book.title -- "Foucault's pendulum"
getTitle b = b.title
-- Works on all records with a title (but doesn't require any other field)
getTitle book -- "Foucault's pendulum"
getTitle {title: "Weekend in Monaco", artist: "The Rippingtons"} -- "Weekend in Monaco"
-- Update a record
changeTitle b t = b {title = t}
changeTitle book "Ill nome della rosa" -- {title: "Ill nome della
-- rosa", author: "Umberto Eco"}
--
-- 4. Functions
sumOfSquares x y = x*x+y*y
sumOfSquares 3 4 -- 25
-- In psci you have to write `let` in front of the function to get a
-- top level binding
mod x y = x % y
mod 3 2 -- 1
-- Infix application of function
3 `mod` 2 -- 1
-- function application have higher precedence than all other
-- operators
sumOfSquares 3 4 * sumOfSquares 4 5 -- 1025
-- Conditional
abs' n = if n>=0 then n else -n
abs' (-3) -- 3
-- Guarded equations
abs n | n >= 0 = n
| otherwise = -n
-- Pattern matching
-- Note the type signature, input is an array of numbers The pattern
-- matching destructures and binds the array into parts
first :: [Number] -> Number
first (x:_) = x
first [3,4,5] -- 3
second :: [Number] -> Number
second (_:y:_) = y
second [3,4,5] -- 4
sumTwo :: [Number] -> [Number]
sumTwo (x:y:rest) = (x+y) : rest
sumTwo [2,3,4,5,6] -- [5,4,5,6]
-- sumTwo doesn't handle when the array is empty or just have one
-- element in which case you get an error
sumTwo [1] -- Failed pattern match
-- Complementing patterns to match
-- Good ol' Fibonacci
fib 1 = 1
fib 2 = 2
fib x = fib (x-1) + fib (x-2)
fib 10 -- 89
-- Use underscore to match any, where you don't care about the binding name
isZero 0 = true
isZero _ = false
-- Pattern matching on records
ecoTitle {author = "Umberto Eco", title = t} = Just t
ecoTitle _ = Nothing
ecoTitle book -- Just ("Foucault's pendulum")
ecoTitle {title: "The Quantum Thief", author: "Hannu Rajaniemi"} -- Nothing
-- ecoTitle requires both field to type check:
ecoTitle {title: "The Quantum Thief"} -- Object does not have property author
-- Lambda expressions
(\x -> x*x) 3 -- 9
(\x y -> x*x + y*y) 4 5 -- 41
sqr = \x -> x*x
-- Currying
add x y = x + y -- is equivalent with
add = \x -> (\y -> x+y)
add3 = add 3
:t add3 -- Prim.Number -> Prim.Number
-- Forward and backward function composition
-- drop 3 followed by taking 5
(drop 3 >>> take 5) (1..20) -- [4,5,6,7,8]
-- take 5 followed by dropping 3
(drop 3 <<< take 5) (1..20) -- [4,5]
-- Operations using higher order functions
even x = x % 2 == 0
filter even (1..10) -- [2,4,6,8,10]
map (\x -> x+11) (1..5) -- [12,13,14,15,16]
-- Requires purescript-foldable-traversabe (Data.Foldable)
foldr (+) 0 (1..10) -- 55
sum (1..10) -- 55
product (1..10) -- 3628800
-- Testing with predicate
any even [1,2,3] -- true
all even [1,2,3] -- false
```
|
