Allow empty strings

src/parser.js

@@ -89,10 +89,19 @@ module.exports = class Parser {
 
   string() {
     this.tokenStream.eat(tokenTypes.QUOTE)
+
+    let value = ''
+
+    if (this.tokenStream.peek().type === tokenTypes.LITERAL) {
+      value = this.tokenStream.eat(tokenTypes.LITERAL).value
+    }
+
     let node = new AST.String({
-      value: this.tokenStream.eat(tokenTypes.LITERAL).value
+      value: value
     })
+
     this.tokenStream.eat(tokenTypes.QUOTE)
+
     return node
   }
 

test/parser.js

@@ -43,3 +43,20 @@ test('parses token stream into a tree', t => {
     })
   ])
 })
+
+test('allow empty strings', t => {
+  t.plan(1)
+  const lexer = new Lexer()
+  const tokenStream = lexer.scan('(p "")')
+  const parser = new Parser(tokenStream)
+  const tree = parser.parse()
+
+  t.deepEqual(tree, [
+    new AST.Application({
+      functionName: new AST.Identifier({ name: 'p' }),
+      args: [
+        new AST.String({ value: '' })
+      ]
+    })
+  ])
+})