Create easylang.html.markdown (#4262)

easylang.html.markdown

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+---
+language: Easylang
+contributors:
+    - ["chkas", "https://github.com/chkas"]
+filename: easylang.el
+---
+
+**Easylang** is a simple programming language with built-in graphical functions and an easy-to-use and offline usable browser IDE. Its simple syntax and semantics make it well suited as a teaching and learning programming language. You can also use it to write graphical applications that you can embed in a web page. 
+
+*Easylang* is statically typed and has as data types only strings and numbers (floating point), resizeable arrays of strings and numbers and arrays of arrays.
+
+[The browser IDE](https://easylang.online/ide/) includes various tutorials, including one for beginners.
+
+```
+print "Hello world"
+#
+# number variable (64 bit floating point)
+#
+h = 3.14
+print h
+#
+# string variable
+#
+str$ = "monkey"
+# strings can grow
+str$ &= " circus" 
+print str$
+#
+# blocks end with 'end' or a dot, a newline has no
+# other meaning than a space
+#
+for i = 1 to 5
+  sum += i * i
+.
+print sum
+#
+# functions have value and reference
+# parameters, no return values
+#
+func gcd a b . res .
+  # a and b are value parameters
+  # res is a reference parameter
+  while b <> 0
+    # h is a local variable, because 
+    # it is first used in the function
+    h = b
+    b = a mod b
+    a = h
+  .
+  res = a
+.
+call gcd 120 35 r
+print r
+#
+# strings can be concatenated and numbers are
+# automatically converted to strings
+#
+print "1 + 2 = " & 1 + 2
+#
+# array of numbers
+#
+a[] = [ 2.1 3.14 3 ]
+#
+# arrays can grow
+a[] &= 4
+print a[]
+#
+# arrays, strings and numbers are copied by value
+#
+b[] = a[]
+a[] &= 4
+print a[] ; print b[]
+#
+# array swapping ist fast
+#
+swap a[] b[]
+print a[] ; print b[]
+# 
+# array of strings
+#
+fruits$[] = [ "apple" "banana" "orange" ]
+#
+# for-in iterates over the elements of an array
+#
+for fruit$ in fruits$[]
+  print fruit$
+.
+#
+# strings are also used for single characters
+#
+letters$[] = str_chars "ping"
+print letters$[]
+letters$[1] = "o"
+print str_join letters$[]
+#
+# 2-dimensional arrays are arrays of arrays
+# this defines 3 arrays with length 4
+#
+len a[][] 3
+for i range len a[][]
+  len a[i][] 4
+.
+a[1][2] = 99
+print a[][]
+#
+# builtin functions
+if sin 90 = 1
+  print "angles are in degree"
+.
+print pow 2 8
+# seconds since 1970
+print floor sys_time
+# random numbers
+print randomf
+print random 6 + 1
+# 
+# hour and minutes
+print substr time_str sys_time 11 5
+# 
+print str_ord "A"
+print str_chr 65
+# 
+# set number format
+numb_fmt 0 4
+print sqrt 2
+print pi
+print logn 10
+# 
+a$[] = str_split "10,15,22" ","
+print a$[]
+print 2 * number a$[0]
+print len a$[]
+print len "Hello"
+#
+# With 'break n' you can leave nested loops and a function
+#
+names$[] = [ ]
+func name2id name$ . id .
+  for id range len names$[]
+    if names$[id] = name$
+      # leave loop and function
+      break 2
+    .
+  .
+  names$[] &= name$
+.
+call name2id "alice" id ; print id
+call name2id "bob" id ; print id
+call name2id "alice" id ; print i
+#
+# with 'repeat' you can make loops, which you can leave
+# in the loop body using 'until'
+#
+sum = 0
+repeat
+  s$ = input
+  until s$ = ""
+  sum += number s$
+.
+print "sum: " & sum
+#
+# "input" reads a string from the "input_data" section, 
+# if it exists, otherwise via a prompt.
+#
+input_data
+10
+-2
+6
+```
+
+Built-in graphic primitives and event-driven programming
+
+```
+# simple drawing with the mouse
+# 
+set_linewidth 4
+set_color 900
+# the colors are coded from 0 to 999, with 
+# the left digit specifying the red component,
+# the middle digit the green component and
+# the right digit the blue component. 
+# 
+on mouse_down
+  down = 1
+  move_pen mouse_x mouse_y
+  # moves the drawing pen to the actual mouse position
+  draw_circle 2
+.
+on mouse_up
+  down = 0
+.
+on mouse_move
+  if down = 1
+    draw_line mouse_x mouse_y
+  .
+.
+```
+
+```
+# an animated pendulum
+#
+on animate
+  # The animate event occurs after each screen refresh.
+  #
+  clear_screen
+  move_pen 50 50
+  draw_circle 1
+  x = 50 + 40 * sin ang
+  y = 50 - 40 * cos ang
+  draw_line x y
+  draw_circle 5
+  vel += sin ang / 5
+  ang += vel
+.
+ang = 10
+```
+
+* [More about Easylang](https://easylang.online/)
+
+* [Source code](https://github.com/chkas/easylang)
+