Parse variables

Author: mudge

lib/expression_parser.rb

@@ -1,6 +1,18 @@
 require_relative 'vm_writer'
 
 class ExpressionParser
+  Number = Struct.new(:value) do
+    def emit(vm_writer, _symbol_table)
+      vm_writer.write_push('constant', value)
+    end
+  end
+
+  Variable = Struct.new(:value) do
+    def emit(vm_writer, symbol_table)
+      vm_writer.write_push(symbol_table.kind_of(value), symbol_table.index_of(value))
+    end
+  end
+
   attr_reader :tokenizer
   private :tokenizer
 
@@ -9,12 +21,15 @@ def initialize(tokenizer)
   end
 
   def parse
-    number = tokenizer.int_val
+    case tokenizer.token_type
+    when Tokenizer::INT_CONST
+      number = tokenizer.int_val
+
+      Number.new(number)
+    else
+      identifier = tokenizer.identifier
 
-    Struct.new(:value) {
-      def emit(vm_writer)
-        vm_writer.write_push('constant', value)
-      end
-    }.new(number)
+      Variable.new(identifier)
+    end
   end
 end

spec/unit/expression_parser_spec.rb

@@ -1,5 +1,6 @@
 require 'tokenizer'
 require 'expression_parser'
+require 'symbol_table'
 
 RSpec.describe ExpressionParser do
   it 'emits VM code for numeric constants' do
@@ -9,7 +10,7 @@
     result = ExpressionParser.new(tokenizer).parse
     output = StringIO.new
     vm_writer = VMWriter.new(output)
-    result.emit(vm_writer)
+    result.emit(vm_writer, SymbolTable.new)
 
     expect(output.string).to eq("push constant 1\n")
   end
@@ -21,8 +22,23 @@
     result = ExpressionParser.new(tokenizer).parse
     output = StringIO.new
     vm_writer = VMWriter.new(output)
-    result.emit(vm_writer)
+    result.emit(vm_writer, SymbolTable.new)
 
     expect(output.string).to eq("push constant 2\n")
   end
+
+  it 'emits VM code for variables' do
+    tokenizer = Tokenizer.new('a')
+    tokenizer.advance
+
+    symbol_table = SymbolTable.new
+    symbol_table.define('a', :int, :static)
+
+    result = ExpressionParser.new(tokenizer).parse
+    output = StringIO.new
+    vm_writer = VMWriter.new(output)
+    result.emit(vm_writer, symbol_table)
+
+    expect(output.string).to eq("push static 0\n")
+  end
 end