Initial Release

README.md

@@ -18,6 +18,7 @@ Goto is a dynamically typed programming language written to support all the scri
 - Grouped Expressions
 - Functions
 - Scopes
+- Comments
 - Error Handling
 - Built in Functions: `append`, `print`, `len`
 
@@ -66,7 +67,12 @@ To execute a goto-script, pass the name to the interpreter:
 
     $ goto sample.to
 
-To drop into goto-repl, type `goto`. 
+Scripts can be made executable by adding a suitable shebang line:
+
+    #!/usr/bin/env goto
+
+
+To drop into goto-repl, type `goto`. To exit from repl, just type `exit` or `Ctrl + D`.
 
 ## 5. Syntax
 
@@ -92,8 +98,8 @@ The datatypes of all the variables need not be the same.
 Goto supports hiding of global variable in block constructs
 
     var a = 4;
-    if true { var a = 5; print(a);} //prints 5
-    print(a); //prints 4
+    if true { var a = 5; print(a);} # prints 5
+    print(a); # prints 4
 
 
 ### 5.2 Arithmetic operations
@@ -111,19 +117,19 @@ List is a data structure that organizes items by linear sequence. It can hold mu
 Lists are 0-indexed. Elements can be accessed using []. Similar indexing exists for strings.
 
     var a = [1, true, "array"];
-    a[1] // returns true
-    a[2][3] // returns "a"
+    a[1] # returns true
+    a[2][3] # returns "a"
 
 ### 5.4 Builtin functions
 Goto currently supports 3 built-in functions:
 1. `len`: Returns the length of string or a list.
 
-    len("goto") //returns 4
+    len("goto") # returns 4
 
 2. `append`: appends a token at the end of an array
 
     var a = [1, 2];
-    append(a, 3) // a becomes [1, 2, 3]
+    append(a, 3) # a becomes [1, 2, 3]
 
 3. `print`: prints the content of parameters to STDOUT. It can take multiple arguments.
 
@@ -143,7 +149,7 @@ Goto defines function using `func` followed by an identifier and a parameter lis
 You can define local functions inside a block statement with limited scope.
 
     func addTwo(x) {
-      func addOne(x) { // addOne() is limited to addTwo()'s scope
+      func addOne(x) { # addOne() is limited to addTwo()'s scope
         return x + 1;
       }
       x = addOne(x);
@@ -163,7 +169,7 @@ Goto supports if-else-if statements.
     } else {
       c = 30; 
     }
-    print(c); //returns 20
+    print(c); # returns 20
 
 ### 5.7 For-loop statements
 Goto has supports for-loop statements.
@@ -189,6 +195,10 @@ There are three control flow statements in goto:
 
 3. `return`: It is used to terminate a function. It may also be used to return values from functions.  
 
+### 5.9 Comments
+Single Line comments are supported by goto.
+
+    # This is a comment
 
 ## 6. Contributing
 If you spot anything that seems wrong, please do [report an issue](https://github.com/pandeykartikey/goto/issues).

lexer/lexer.go

@@ -36,6 +36,14 @@ func (l *Lexer) skipWhitespace() {
 	}
 }
 
+func (l *Lexer) skipComments() {
+	if l.ch == '#' {
+		for l.ch != '\n' && l.ch != 0 {
+			l.readChar()
+		}
+	}
+}
+
 func (l *Lexer) readSequence(f func(byte) bool) string {
 	position := l.position
 
@@ -79,6 +87,9 @@ func (l *Lexer) NextToken() token.Token {
 			tok.Literal = l.readSequence(isDigit)
 			tok.Type = token.INT
 			return tok
+		} else if l.ch == '#' {
+			l.skipComments()
+			return l.NextToken()
 		} else {
 			tok = newToken(token.ILLEGAL, l.ch)
 		}

main.go

@@ -41,8 +41,7 @@ func main() {
 			fmt.Println(result.Inspect())
 		}
 	} else {
-		fmt.Printf("GoTo 0.1.0\n")
-
+		fmt.Println("Goto 0.1.0")
 		repl.Start()
 	}
 }

parser/parser.go

@@ -253,6 +253,10 @@ func (p *Parser) parseExpressionList() *ast.ExpressionList {
 		return args
 	}
 
+	if p.currTokenIs(token.EOF) {
+		p.errors = append(p.errors, "End Of File encountered while parsing")
+	}
+
 	return nil
 }
 
@@ -337,7 +341,7 @@ func (p *Parser) parseAssignment(isExpression bool) *ast.Assignment {
 
 	assign.ValueList = p.parseExpressionList()
 
-	if len(assign.ValueList.Expressions) != len(assign.NameList.Identifiers) {
+	if assign.ValueList == nil || assign.NameList == nil || len(assign.ValueList.Expressions) != len(assign.NameList.Identifiers) {
 		p.errors = append(p.errors, "Mismatch in number of values on both side of =")
 	}
 
@@ -582,6 +586,8 @@ func (p *Parser) parseStatement() ast.Statement {
 		return nil
 	case token.SEMI:
 		return nil
+	case token.EOF:
+		return nil
 	case token.IDENT:
 		if p.peekTokenIs(token.COMMA) || p.peekTokenIs(token.ASSIGN) {
 			return p.parseAssignment(false)

repl/repl.go

@@ -20,6 +20,7 @@ func Start() {
 
 	term := liner.NewLiner()
 	defer term.Close()
+	term.SetCtrlCAborts(true)
 
 	env := object.NewEnvironment()
 	code := ""
@@ -30,11 +31,21 @@ func Start() {
 		line, err := term.Prompt(prompt)
 
 		if err != nil {
-			fmt.Println("Aborted")
+			if err == liner.ErrPromptAborted {
+				code = ""
+				prompt = PS1
+				continue
+			} else {
+				fmt.Println("Aborted")
+			}
+			break
+		}
+
+		if line == "exit" {
 			break
 		}
 
-		code += line
+		code += "\n" + line
 
 		l := lexer.New(code)
 		p := parser.New(l)

sample.to

@@ -1,5 +1,7 @@
-func identity(x) {
+#!/usr/bin/env goto
+
+func identity(x) { # An identity function
 	return x;
 }
 
-print(identity(4)); 
+print(identity(4));