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1)  Built in operators:
    +,-,*,/,%,==,!=,<=,>=,<,>,;
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2)  Integers and floats in arithmetics:
    1 or 2.33333 or 0.34 or .34
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3)  Arbitrary nesting of parentheses:
    (1+2*(5+((3+4)*3)-6/2)+7*2)\n    => 61
-----------------------------------------
4)  Comments:
    # A comment until the end of the line
    /* A longer comment that
       spans multiple lines
     */
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5)  Built in keywords:
    TRUE,FALSE,NULL,IF,ELSE,END
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6)  Built in functions:
    HELP,ENV,SIZE,SPLIT,ROUND,MIN,MAX
    SUM,MULT,AVG, PRINT, PRINT_LINE
    TO_INT, TO_FLOAT, TO_ARRAY, AVG_SUM
    MATCHING_IDS, VALUES_OF_TYPE
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7)  Standard library functions:
    foreach_in, inject, map, select
    reject, in_groups_of, sum_of_type
    avg_sum_of_type, avg_range_sum_of_type
    total_range_sum_of_type, ratio
    year_from_date, month_from_date,
    hash_values, hash_value_sum,
    avg_hash_value_sum, hash_range_values,
    hash_range_value_sum,
    avg_hash_range_value_sum
-----------------------------------------
8)  Access the current environment:
    ENV; (your output may differ)
    => { :a => 3, :foo => 5 }
    Given the following environment:
    { :a => 1, :b => 2, :c => 3 }
    ENV['a']
    => 1
    ENV['a'..'b']
    => { :a => 1, :b => 2 }
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9)  Numeric variables and literals
    3;
    => 3
    a = 3;
    => 3
    a;
    => 3
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10) String variables and literals
    "This is a string";    
    => "This is a string";
    'This is a string';
    => "This is a string";
    s1 = "This is a string"; s1;
    => "This is a string"
    s2 = 'This is a string'; s2;
    => "This is a string"
    SIZE(s1);
    => 16
    SIZE("foo");
    => 3
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11) Variables and closure applications
    a = 3; foo = 5;
    calc = fun(x,y) { (x + y) * a + foo };
    calc(2,2);
    => 17
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12) Array variables and literals
    arr = [1, [fun(){2}()], fun(x){x}(3)]
    SIZE(arr);
    => 3
    SIZE([1,2,3]);
    => 3
    [1,2,3] + [4,[5,6]];
    => [1,2,3,4,[5,6]]
    [1,2,3] - [[1],2,3];
    => [1]
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13) Hash variables and literals
    h = { 1 => fun(){2}(), 'a' => 'foo' }
    SIZE(h);
    => 2
    h[1];
    => 'fun(){2}()'
    h['a'];
    => 'foo'
    SIZE({ 1 => 2});
    => 1
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14) Range variables and literals
    range_including_upper = 1..5
    => [ 1, 2, 3, 4, 5 ]
    SIZE(range_including_upper);
    => 5
    range_excluding_upper = 1...5
    => [ 1, 2, 3, 4 ]
    SIZE(range_excluding_upper);
    => 4
    SIZE([1..5);
    => 5
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15) Conditional branching and recursion:
    factorial = fun(x) {      
      if(x == 0)
        1
      else
        x * factorial(x - 1)
      end
    }
    factorial(5);
    => 120
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16) Conditional branching:
    foo = fun(x) {
      if(x == 0)
        0
      elsif(x == 1)
        1
      else
        2
      end
    }
    foo(0);
    => 0
    foo(1);
    => 1
    foo(2);
    => 2
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17) case expressions:
    foo = fun(x) {
      case x
      when NULL then NULL
      when 0    then 0
      when 1    then 1
      when 2    then 2
      else          
        3
      end
    }
    foo(1);
    => 1
    foo(3);
    => 3
-----------------------------------------