Added if statements

interpreter.js

@@ -1,5 +1,5 @@
 const { runtimeError } = require('./errors')
-const { Binary, Unary, Literal, Var, Grouping, Block, ExpressionStatement, VarStatement, PrintStatement, Assignment } = require('./types')
+const { Binary, Unary, Literal, Var, Grouping, Block, ExpressionStatement, VarStatement, PrintStatement, Assignment, Condition } = require('./types')
 const Environment = require('./environment')
 const tokenizer = require('./tokenizer')
 const token = tokenizer.tokenEnum
@@ -26,8 +26,10 @@ class Interpreter {
   evaluate (expr) {
     if (expr instanceof Block) return this.visitBlock(expr)
     else if (expr instanceof Assignment) return this.visitAssignment(expr)
-    else if (expr instanceof PrintStatement) return this.visitPrintStatement(expr)
+    else if (expr instanceof Condition) return this.visitCondition(expr)
     else if (expr instanceof VarStatement) return this.visitVarStatement(expr)
+    else if (expr instanceof PrintStatement) return this.visitPrintStatement(expr)
+    else if (expr instanceof ExpressionStatement) return this.visitGrouping(expr) // Doesn't need it's own, it can just evaluate like grouping
     else if (expr instanceof Grouping) return this.visitGrouping(expr)
     else if (expr instanceof Var) return this.visitVar(expr)
     else if (expr instanceof Literal) return this.visitLiteral(expr)
@@ -39,7 +41,7 @@ class Interpreter {
   visitGrouping (expr) { return this.evaluate(expr.expression) }
   visitPrintStatement (expr) {
     const val = this.evaluate(expr.expression)
-    console.log(val.toString())
+    console.log(!val ? 'nil' : val.toString())
     return val
   }
   visitVar (variable) {
@@ -59,6 +61,15 @@ class Interpreter {
     return null
   }
 
+  visitCondition (expr) {
+    if (isTruthy(this.evaluate(expr.condition))) {
+      this.evaluate(expr.thenBranch)
+    } else if (expr.elseBranch) {
+      this.evaluate(expr.elseBranch)
+    }
+    return null
+  }
+
   interpretBlock (statements, env) {
     const prevEnvironment = this.environment
     try {

parser.js

@@ -1,5 +1,5 @@
 const tokenizer = require('./tokenizer')
-const { Binary, Unary, Var, Literal, Grouping, PrintStatement, ExpressionStatement, VarStatement, Assignment, Block } = require('./types')
+const { Binary, Unary, Var, Literal, Grouping, PrintStatement, ExpressionStatement, VarStatement, Assignment, Block, Condition } = require('./types')
 const { parseError: ParseError } = require('./errors')
 const token = tokenizer.tokenEnum
 
@@ -55,12 +55,24 @@ class Parser {
   }
 
   statement () {
+    if (this.match(token.IF)) return this.ifStatement()
     if (this.match(token.PRINT)) return this.printStatement()
     if (this.match(token.LEFT_BRACE)) return new Block(this.block())
 
     return this.expressionStatement()
   }
 
+  ifStatement () {
+    this.consume(token.LEFT_PAREN, 'Expected "(" after "if"')
+    const cond = this.expression()
+    this.consume(token.RIGHT_PAREN, 'Expected ")" after expression')
+    const ifBranch = this.statement()
+    let elseBranch = null
+    if (this.match(token.ELSE)) elseBranch = this.statement()
+
+    return new Condition(cond, ifBranch, elseBranch)
+  }
+
 
   block () {
     let statements = []

types.js

@@ -54,6 +54,14 @@ class Block {
   }
 }
 
+class Condition {
+  constructor (condition, thenBranch, elseBranch) {
+    this.condition = condition
+    this.thenBranch = thenBranch
+    this.elseBranch = elseBranch
+  }
+}
+
 
 module.exports = {
   Var,
@@ -62,6 +70,7 @@ module.exports = {
   Block,
   Literal,
   Grouping,
+  Condition,
   ExpressionStatement,
   PrintStatement,
   VarStatement,