add: NullLiteral

src/ast/compiler/ast.interface.ts

@@ -6,7 +6,7 @@
  * - statements will not return a value
  * - statement example -> let x = 45
  */
-export type NodeType = 'Program' | 'NumericLiteral' | 'Identifier' | 'BinaryExpr'
+export type NodeType = 'Program' | 'NumericLiteral' | 'NullLiteral' | 'Identifier' | 'BinaryExpr'
 
 /** Abstract Statement Interface that include statement kind */
 export interface IStatement {
@@ -51,3 +51,9 @@ export interface INumericLiteral extends IExpression {
   kind: 'NumericLiteral'
   value: number
 }
+
+/** Null Literal Expression Node Type */
+export interface INullLiteral extends IExpression {
+  kind: 'NullLiteral'
+  value: 'null'
+}

src/ast/compiler/parser.ts

@@ -8,6 +8,7 @@ import {
   IBinaryExpression,
   INumericLiteral,
   IIdentifierExpression,
+  INullLiteral,
 } from './ast.interface'
 
 /**
@@ -104,14 +105,17 @@ export class Parser {
     switch (tokenType) {
       case TokenType.Identifier:
         return { kind: 'Identifier', symbol: this.eat().value } as IIdentifierExpression
+      case TokenType.Null:
+        this.eat() // advance past null keyword
+        return { kind: 'NullLiteral', value: 'null' } as INullLiteral
       case TokenType.Number:
         return { kind: 'NumericLiteral', value: parseFloat(this.eat().value) } as INumericLiteral
       case TokenType.OpenParen:
         this.eat() // eat open paren
         const value = this.parseExpr()
         this.expect(
           TokenType.CloseParen,
-          'Unexpected token found inside parenthesised expression. Expected closing parenthesis',
+          'Unexpected token found inside parenthesised expression. Expected closing parenthesis'
         ) // eat close paren
         return value
       default:

src/lexer/lexer.ts

@@ -44,9 +44,9 @@ export class Lexer {
           const reserved = KEYWORDS[ident]
           // if value is not undefined, the identifier is recognized keyword
           if (typeof reserved == 'number') {
-            tokens.push(this.token(ident, TokenType.Identifier))
-          } else {
             tokens.push(this.token(ident, reserved))
+          } else {
+            tokens.push(this.token(ident, TokenType.Identifier))
           }
         } else if (this.isSkippable(src[0])) {
           src.shift() // skip the current character