BAPFS - Lecture 3

.vscode/settings.json

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+{
+	"editor.formatOnType": true
+}

Editor/Lecture.3..gd

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+extends Node
+
+const JsonBeautifier = preload("res://ThirdParty/json_beautifier.gd")
+
+# This closesly follows the source provided in the lectures.
+# Later on after the lectures are complete or when I deem
+# Necessary there will be heavy refactors.
+
+const TokenType = \
+{
+	Program    = "Program",
+	
+	# Comments
+	CommentLine      = "CommentLine",
+	CommentMultiLine = "CommentMultiLine",
+	
+	# Formatting
+	Whitespace = "Whitespace",
+	
+	# Literals
+	Number     = "Number",
+	String     = "String"
+}
+
+const TokenSpec = \
+{
+	TokenType.CommentLine      : "^\/\/.*",
+	TokenType.CommentMultiLine : "^\/\\*[\\s\\S]*?\\*\/",
+	TokenType.Whitespace       : "^\\s+",
+	TokenType.Number           : "\\d+",
+	TokenType.String           : "^\"[^\"]*\""
+}
+
+class Token:
+	var Type  : String
+	var Value : String
+	
+	func toDict():
+		var result = \
+		{
+			Type  = self.Type,
+			Value = self.Value
+		}
+		return result
+
+class Tokenizer:
+	var SrcTxt : String
+	var Cursor : int;
+	
+	# Sets up the tokenizer with the program source text.
+	func init(programSrcText):
+		SrcTxt = programSrcText
+		Cursor = 0
+	
+	# Provides the next token in the source text.
+	func next_Token():
+		if self.reached_EndOfTxt() == true :
+			return null
+			
+		var srcLeft = self.SrcTxt.substr(Cursor)
+		var regex   = RegEx.new()
+		var token   = Token.new()
+		
+		for type in TokenSpec :
+			regex.compile(TokenSpec[type])
+			
+			var result = regex.search(srcLeft)
+			if  result == null :
+				continue
+				
+			# Skip Comments
+			if type == TokenType.CommentLine || type == TokenType.CommentMultiLine :
+				self.Cursor += result.get_string().length()
+				return next_Token()
+				
+			# Skip Whitespace
+			if type == TokenType.Whitespace :
+				var addVal = result.get_string().length()
+				self.Cursor += addVal
+				
+				return next_Token()
+				
+			token.Type   = type
+			token.Value  = result.get_string()
+			self.Cursor += ( result.get_string().length() -1 )
+				
+			return token
+			
+		var assertStrTmplt = "next_token: Source text not understood by tokenizer at Cursor pos: {value}"
+		var assertStr      = assertStrTmplt.format({"value" : self.Cursor})
+		assert(true != true, assertStr)
+		return null
+	
+	func reached_EndOfTxt():
+		return self.Cursor >= ( self.SrcTxt.length() - 1 )
+		
+var GTokenizer = Tokenizer.new()
+
+
+class SyntaxNode:
+	var Type  : String
+	var Value # Not specifing a type implicity declares a Variant type.
+	
+	func toDict():
+		var result = \
+		{ 
+			Type  = self.Type,
+			Value = self.Value
+		}
+		return result
+
+class ProgramNode:
+	var Type : String
+	var Body : Object
+	
+	func toDict():
+		var result = \
+		{
+			Type = self.Type,
+			Body = self.Body.toDict()
+		}
+		return result
+
+class Parser:
+	var TokenizerRef : Tokenizer
+	var NextToken    : Token
+	
+	func eat(tokenType):
+		var currToken = self.NextToken
+		
+		assert(currToken != null, "eat: NextToken was null")
+		
+		var assertStrTmplt = "eat: Unexpected token: {value}, expected: {type}"
+		var assertStr      = assertStrTmplt.format({"value" : currToken.Value, "type" : tokenType})
+		
+		assert(currToken.Type == tokenType, assertStr)
+		
+		self.NextToken = self.TokenizerRef.next_Token()
+		
+		return currToken
+	
+	# Literal
+	#	: NumericLiteral
+	#	: StringLiteral
+	#	;
+	func parse_Literal():
+		match self.NextToken.Type :
+			TokenType.Number:
+				return parse_NumericLiteral()
+			TokenType.String:
+				return parse_StringLiteral()
+				
+		assert(false, "parse_Literal: Was not able to detect valid literal type from NextToken")
+		
+	# NumericLiteral
+	#	: Number
+	#	;
+	#
+	func parse_NumericLiteral():
+		var Token = self.eat(TokenType.Number)
+		var \
+		node       = SyntaxNode.new()
+		node.Type  = TokenType.Number
+		node.Value = int( Token.Value )
+		
+		return node
+	
+	# StringLiteral
+	#	: String
+	#	;
+	#
+	func parse_StringLiteral():
+		var Token = self.eat(TokenType.String)
+		var \
+		node = SyntaxNode.new()
+		node.Type  = TokenType.String
+		node.Value = Token.Value.substr( 1, Token.Value.length() - 2 )
+
+		return node
+	
+	# Program
+	# 	: Literal
+	#	;
+	#
+	func parse_Program():
+		var \
+		node      = ProgramNode.new()
+		node.Type = TokenType.Program
+		node.Body = parse_Literal()
+		
+		return node
+
+	# Parses the text program description into an AST.
+	func parse(TokenizerRef):
+		self.TokenizerRef = TokenizerRef
+		
+		NextToken = TokenizerRef.next_Token()
+		
+		return parse_Program()
+
+var GParser = Parser.new()
+
+
+var ProgramDescription : String
+
+func test():
+	GTokenizer.init(ProgramDescription)
+	
+	var ast = GParser.parse(GTokenizer)
+	
+	print(JsonBeautifier.beautify_json(to_json(ast.toDict())))
+	
+
+# Main Entry point.
+func _ready():
+	# Numerical test
+	ProgramDescription = "47"
+	test()
+	
+	# String Test
+	ProgramDescription = "\"hello\""
+	test()
+
+	# Whitespace test
+	ProgramDescription = "     \"we got past whitespace\"       "
+	test()
+	
+	# Comment Single Test
+	ProgramDescription = \
+	"""
+	// Testing a comment    
+	\"hello sir\"       
+	"""
+	test()
+	
+	# Comment Multi-Line Test
+	ProgramDescription = \
+	"""
+	/**
+	*
+	* Testing a comment    
+	*/
+	\"may I have some grapes\"       
+	"""
+	test()
+	
+	# Multi-statement test
+	ProgramDescription = \
+	"""
+	// Testing a comment    
+	\"hello sir\";
+	
+	/**
+	*
+	* Testing a comment    
+	*/
+	\"may I have some grapes\";    
+	"""
+	test()
+
+# Called every frame. 'delta' is the elapsed time since the previous frame.
+#func _process(delta):
+#	pass
+
+
+

Editor/Lecture.3.tscn

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+[gd_scene load_steps=2 format=2]
+
+[ext_resource path="res://Lecture.3..gd" type="Script" id=1]
+
+[node name="Control" type="Control"]
+anchor_right = 1.0
+anchor_bottom = 1.0
+script = ExtResource( 1 )

Editor/project.godot

@@ -21,7 +21,7 @@ _global_script_class_icons={
 [application]
 
 config/name="Parser"
-run/main_scene="res://Lecture.2.tscn"
+run/main_scene="res://Lecture.3.tscn"
 boot_splash/image="res://Branding/RDP_Class_cover_small.png"
 config/icon="res://Branding/RDP_Class_cover_small.png"