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diff --git a/phel.html.markdown b/phel.html.markdown new file mode 100644 index 00000000..39d8bae2 --- /dev/null +++ b/phel.html.markdown @@ -0,0 +1,333 @@ +--- +language: phel +filename: learnphel.phel +contributors: + - ["Chemaclass", "https://github.com/Chemaclass"] +--- + +[Phel](https://phel-lang.org/) is a functional programming language that compiles to PHP. +It is a dialect of Lisp inspired by Phel and Janet. + +## Features +- Built on PHP's ecosystem +- Good error reporting +- Persistent Datastructures (Lists, Vectors, Maps and Sets) +- Macros +- Recursive functions +- Powerful but simple Syntax +- REPL + +```phel +# Comments begin with a # character and continue until the end of the line. There are no multi-line comments. + +# Phel is written in "forms", which are just +# lists of things inside parentheses, separated by whitespace. + +# The first call in a file should be ns, to set the namespace +(ns learn-phel) + +# More basic examples: + +# str will create a string out of all its arguments +(str "Hello" " " "World") # => "Hello World" + +# Math is straightforward +(+ 1 1) # => 2 +(- 2 1) # => 1 +(* 1 2) # => 2 +(/ 2 1) # => 2 + +# Equality is = +(= 1 1) # => true +(= 2 1) # => false + +# You need not for logic, too +(not true) # => false + +# Nesting forms works as you expect +(+ 1 (- 3 2)) # = 1 + (3 - 2) => 2 + +# Phel inherits PHP under the hood, so it can use native PHP (functions and classes) without any additional cost +# by using the `php/` prefix to all PHP native functions. + +# Types +############# + +# Booleans are similar as the native PHP ones + +nil +true +false + +# Symbols are used to name functions and variables in Phel +# For example: symbol, snake_case_symbol, my-module/my-function + +# Keywords are like symbols that begin with a colon character. However, they are used as constants rather than a name for something. + +:keyword +:0x0x0x +:: + +# Numbers in Phel are equivalent to numbers in PHP + +1337 # integer ++1337 # positive integer +-1337 # negative integer + +1.234 # float ++1.234 # positive float +-1.234 # negative float +1.2e3 # float +7E-10 # float + +# Strings are surrounded by double quotes. They almost work the same as PHP double quoted strings. +# A string can be written in multiple lines. The line break character is then ignored by the reader. + +"hello world" + +"this is\na\nstring" + +"this +is +a +string." + +"use backslack to escape \" string" + +"the dollar must not be escaped: $ or $abc just works" + + +# Collections & Sequences +############# + +# Lists are linked-list data structures, while vectors are array-backed. +(type '(1 2 3)) # :list +(type [1 2 3]) # :vector + +# A list would be written as just (1 2 3), but we have to quote +# it to stop the reader thinking it's a function. +# Also, (list 1 2 3) is the same as '(1 2 3) + +# You can produce a (non-lazy) sequence between a range. +(range 1 10 2) # <- (range from to step) +(take 4 (range 10)) + +# Use cons to add an item to the beginning of a list +(cons 4 '(1 2 3)) # => (4 1 2 3) + +# Use push to add, and put to replace an item in a vector +(push [1 2 3] 4) # => (1 2 3 4) +(put [1 2 3] 1 4) # => (1 4 3) + +# Use concat to add lists or vectors together +(concat [1 2] '(3 4)) # => [1 2 3 4] + +# Use filter, map to interact with collections +(map inc [1 2 3]) # => [2 3 4] +(filter even? [1 2 3]) # => [2] + +# Use reduce to reduce them. The initial-value is mandatory +(reduce + 0 [1 2 3 4]) +# => (+ (+ (+ 1 2) 3) 4) +# => 10 + +(reduce push [] '(3 2 1)) +# = (push (push (push [] 3) 2) 1) +# => [3 2 1] + +# Functions +############# + +# Use fn to create new functions. A function always returns its last statement. +(fn [] "Hello World") # => :function + +# You need extra parens to call it +((fn [] "Hello World")) # => "Hello World" + +# You can create a var using def +(def x 1) +x # => 1 + +# Assign a function to a var +(def hello-world (fn [] "Hello World")) +(hello-world) # => "Hello World" + +# You can shorten this process by using defn +(defn hello-world [] "Hello World") + +# The [] is the list of arguments for the function. +(defn hello [name] + (str "Hello " name)) +(hello "Jens") # => "Hello Jens" + +# You can also use this shorthand to create functions: +(def hello2 |(str "Hello " $1)) +(hello2 "Anna") # => "Hello Anna" + +# Functions can pack extra arguments up in a seq for you +(defn count-args [& args] + (str "You passed " (count args) " args: " args)) +(count-args 1 2 3) # => "You passed 3 args: @[1 2 3]" + +# You can mix regular and packed arguments +(defn hello-count [name & args] + (str "Hello " name ", you passed " (count args) " extra args")) +(hello-count "Jesus" 1 2) # => "Hello Jesus, you passed 2 extra args" + + +# Maps +############# + +# Hash maps have faster lookups but don't retain key order. +(type {:a 1 :b 2 :c 3}) # => :hash-map +(type (hash-map :a 1 :b 2 :c 3)) # => :hash-map + +# Maps can use any hashable type as a key, but usually keywords are best +# Keywords are like strings with some efficiency bonuses and they start with `:` +(type :a) # => :keyword + +(def stringmap {"a" 1 "b" 2 "c" 3}) +stringmap # => {"a" 1 "b" 2 "c" 3} + +(def keymap {:a 1 :b 2 :c 3}) +keymap # => {:a 1 :c 3 :b 2} + +# Retrieve a value from a map by calling it as a function +(stringmap "a") # => 1 +(keymap :a) # => 1 + +# Keywords can be used to retrieve their value from a map, too! +(:b keymap) # => 2 + +# Don't try this with strings. +# ("a" stringmap) +# ...Exception: Call to undefined function a() + +# Retrieving a non-present key returns nil +(stringmap "d") # => nil + +# Use put to add new keys to hash-maps +(def newkeymap (put keymap :d 4)) +newkeymap # => {:a 1 :b 2 :c 3 :d 4} + +# But remember, phel types are immutable! +keymap # => {:a 1 :b 2 :c 3} + +# Use unset to remove keys +(unset keymap :a) # => {:b 2 :c 3} + +# Sets +############# + +# A Set contains unique values in random order. + +(type (set 1 2 3)) # => :set +(set 1 2 3 1 2 3 3 2 1 3 2 1) # => (set 1 2 3) + +# Add a member with push +(push (set 1 2 3) 4) # => (set 1 2 3 4) + +# Remove one with unset +(unset (set 1 2 3) 1) # => (set 2 3) + +# Test for existence by using the set as a function: +((set 1 2 3) 1) # => 1 +((set 1 2 3) 4) # => nil + +# There are more functions like: count, union, intersection, difference, etc. + + +# Useful forms +############# + +# Logic constructs in clojure are just macros, and look like everything else +(if false "a" "b") # => "b" +(if false "a") # => nil + +# Use let to create temporary bindings +(let [a 1 b 2] + (> a b)) # => false + +# Group statements together with do +(do + (print "Hello") + "World") #=> "World" (prints "Hello") + +# Functions have an implicit do +(defn print-and-say-hello [name] + (print "Saying hello to " name) + (str "Hello " name)) +(print-and-say-hello "Jeff") #=> "Hello Jeff" (prints "Saying hello to Jeff") + +# So does let +(let [name "Urkel"] + (print "Saying hello to " name) + (str "Hello " name)) # => "Hello Urkel" (prints "Saying hello to Urkel") + +# Use the threading macros (-> and ->>) to express transformations of +# data more clearly. + +# The "Thread-first" macro (->) inserts into each form the result of +# the previous, as the first argument (second item) +(-> + {:a 1 :b 2} + (put :c 3) #=> (put {:a 1 :b 2} :c 3) + (unset :b)) #=> (unset (put {:a 1 :b 2} :c 3) :b) + + +# The double arrow does the same thing, but inserts the result of +# each line at the *end* of the form. This is useful for collection +# operations in particular: +(->> + (range 10) + (map inc) #=> (map inc (range 10)) + (filter odd?)) #=> (filter odd? (map inc (range 10))) + # Result: [1 3 5 7 9] + + +# When you are in a situation where you want more freedom as where to +# put the result of previous data transformations in an +# expression, you can use the as-> macro. With it, you can assign a +# specific name to transformations' output and use it as a +# placeholder in your chained expressions: + +(as-> [1 2 3] input + (map inc input) #=> You can use last transform's output at the last position + (get input 2) #=> and at the second position, in the same expression + (push [4 5 6] input 8 9 10)) #=> or in the middle ! + # Result: [4 5 6 4 8 9 10] + +# PHP +################# + +# PHP has a huge and useful standard library, and you're able to use +# all native functions with the prefix `php/`. +(php/+ 1 2 3) + +# With :use you can use different namespaces. Similar as `use` in PHP. +(ns my\module + (:use \DateTimeImmutable)) + +# You can import functions from other phel files with :require +(ns my\module + (:require phel\test :refer [deftest is])) + +# Use the class name with a "php/new" to make a new instance +(php/new \DateTime) # <a date-time object> + +# Use php/-> to call methods of an object +(def d (php/new \DateTime)) +(php/-> d (getTimestamp)) # <a timestamp> + +# you can do it in one line too +(php/-> (php/new \DateTime) (getTimestamp)) + +# Use php/:: to call static methods +(php/:: \DateTimeImmutable ATOM) # <a timestamp> +``` + +### Further Reading + +This is far from exhaustive, but hopefully it's enough to get you on your feet. + +Read the full documentation in the website: [https://phel-lang.org/](https://phel-lang.org/documentation/getting-started/) |