BookPart 3

Update (10/13/2021): Updated to 3.0.1.2. This includes the beginnings of array support. Also the repl was updated with new commands such as showtree and showcode. showtree lets you view the generated AST and showcode the byte code. The accompanying textbook has been started and the first chapter will be released sometime in the next few weeks. One big change is that after much thought and a number of attempts at designing array support I decided to switch from curley brackets to square brackets for lists. This matches python. Curely brackets will likely be reserved for maps/dictionaries. The same code below has been updated to reflect this change. Note that gif video still shows curely brackets. This will be updated shortly. There is a new binary release to accompany this version.

Update (10/2/2021): The 3.0.1.0 update represents a major rewrite of the AST/compiler and parts of the parser. It now supports a simple object model on strings and lists as well as revising the grammar to take care of the new module syntax. I will also split the parsing into two parts to make it easer to handle memory managements during compile errors. All samples and tests have been updated to the new object syntax.

This repo holds source code for part III of the book series on building an interpreter using Object Pascal (https://www.objectpascalinterpreter.com). the code is now fairly stable but I will continue to tidy up the code and possibly add one or two additional features.

The major outward change in this version includes library support, and a range of small builtin libraries such as math (these will be expanded). The biggest internal change is to separate code generation from syntax analysis in the form of an abstract syntax tree. User functions are also now first-class entities which can be passed around like any other variable. A lot of work has been done on ensure that garbage collection doesn't leak memory.

Example code:

// Quick sort algorithm, depends on recursion
function QSort (numbers, left, right)
  l_ptr = left
  r_ptr = right
  pivot = numbers[left]

  while (left < right) do

        while ((numbers[right] >= pivot) AND (left < right)) do
          right = right - 1
        end

        if (left != right) then
           numbers[left] = numbers[right]
           left = left + 1
        end

        while ((numbers[left] <= pivot) AND (left < right)) do
           left = left + 1
        end

        if (left != right) then
           numbers[right] = numbers[left]
           right = right - 1
        end
  end

  numbers[left] = pivot
  pivot = left
  left = l_ptr
  right = r_ptr

  if (left < pivot) Then
      QSort(numbers, left, pivot-1)
  end

  if (right > pivot) Then
     QSort(numbers, pivot+1, right)
  end 
end

// Driver code to test above   
numbers = [12, 7, 13, 5, 6]
QSort(numbers, 0, numbers.len () - 1) 
res = assertTrueEx (numbers == [5, 6, 7, 12, 13])
if res == "." then
   println("----PASS----")
else
   println("----FAIL----")
end

// Bigger example
numbers = random.randlist (100, 100)
size = numbers.len ()
QSort(numbers, 0, size-1)
println ("Larger example: ", numbers)

Passing functions as arguments:

// Add some user defined funtions
function sqr (x) return x*x; end
function cube (x) return x*x*x; end

function runtest (fcn, x)
   return fcn (x)
end

s = runtest (sqr, 5)
println (s)

s = runtest (cube, 5)
println (s)

Use of modules:

First define a new module called lib.rh:

a1 = 1.234
b1 = 5.678

function sqrt (x)
   return x^0.5
end;

function input (prompt)
   print (prompt + " ");
   return readString()
end

Importing and using the module:

import lib

println (lib.sqrt (25))
println (lib.a1)

Printing out all the colors:

    colors = [
      "Snow",           "FloralWhite",     "LavenderBlush", "OldLace",         "Ivory",                "CornSilk",       "Beige",          "AntiqueWhite",
      "Wheat",          "AliceBlue",       "GhostWhite",    "Lavender",        "Seashell",             "LightYellow",    "PapayaWhip",     "NavajoWhite",
      "Moccasin",       "Burlywood",       "Azure",         "Mintcream",       "Honeydew",             "Linen",          "LemonChiffon",   "BlanchedAlmond",
      "Bisque",         "PeachPuff",       "Tan",           "Yellow",          "DarkOrange",           "Red",            "DarkRed",        "Maroon",
      "IndianRed",      "Salmon",          "Coral",         "Gold",            "Tomato",               "Crimson",        "Brown",          "Chocolate",
      "SandyBrown",     "LightSalmon",     "LightCoral",    "Orange",          "OrangeRed",            "Firebrick",      "SaddleBrown",    "Sienna",
      "Peru",           "DarkSalmon",      "RosyBrown",     "PaleGoldenrod",   "LightGoldenrodYellow", "Olive",          "ForestGreen",    "GreenYellow",
      "Chartreuse",     "LightGreen",      "Aquamarine",    "SeaGreen",        "GoldenRod",            "Khaki",          "OliveDrab",      "Green",
      "YellowGreen",    "LawnGreen",       "PaleGreen",     "MediumAquamarine","MediumSeaGreen",       "DarkGoldenRod",  "DarkKhaki",      "DarkOliveGreen",
      "Darkgreen",      "LimeGreen",       "Lime",          "SpringGreen",     "MediumSpringGreen",    "DarkSeaGreen",   "LightSeaGreen",  "PaleTurquoise",
      "LightCyan",      "LightBlue",       "LightSkyBlue",  "CornFlowerBlue",  "DarkBlue",             "Indigo",         "MediumTurquoise","Turquoise",
      "Cyan",           "PowderBlue",      "SkyBlue",       "RoyalBlue",       "MediumBlue",           "MidnightBlue",   "DarkTurquoise",  "CadetBlue",
      "DarkCyan",       "Teal",            "DeepSkyBlue",   "DodgerBlue",      "Blue",                 "Navy",           "DarkViolet",     "DarkOrchid",
      "Magenta",        "DarkMagenta",     "MediumVioletRed", "PaleVioletRed", "BlueViolet",           "MediumOrchid",   "MediumPurple",   "Purple",
      "DeepPink",       "LightPink",       "Violet",        "Orchid",          "Plum",                 "Thistle",         "HotPink",       "Pink",
      "LightSteelBlue", "MediumSlateBlue", "LightSlateGray","White",           "Lightgrey",            "Gray",            "SteelBlue",     "SlateBlue",
      "SlateGray",      "WhiteSmoke",      "Silver",        "DimGray",         "MistyRose",            "DarkSlateBlue",   "DarkSlategray", "Gainsboro",
      "DarkGray",       "Black"]   

    l = colors.len ()
    for i = 1 to l do
        setColor (colors[i-1])
        print ("Color Test  ");
        if i mod 6 == 0 then
           println() 
        end
    end