[NEW] Expression grouping with parens. (end of part 2)

Makefile

@@ -1,6 +1,7 @@
 build:
 #	ruby test.rb '5-5+3-2-1'
-	ruby test.rb '5*3-5*2+3-9/3-1*1-8/2'
+#	ruby test.rb '5*3-5*2+3-9/3-1*1-8/2'
+	ruby test.rb '5*(3-5)*2+2-9/3-8/2-4*(5+5+5)'
 	nasm -f elf -g -o test.o test.asm
 	ld -o test test.o
 # $? indicates success as per unix convention

compiler.rb

@@ -80,13 +80,19 @@ class Compiler
 
   # Parse and translate a single factor.  Result is in eax.
   def factor
-    emit("mov eax, #{get_num}")
+    if @look == '('
+      match('(')
+      expression
+      match(')')
+    else
+      emit("mov eax, #{get_num}")
+    end
   end
 
   # Parse and translate a single term.  Result is in eax.
   def term
     factor                      # Result in eax.
-    while ['*', '/'].include?(@look)
+    while mulop?
       # Stash the 1st factor on the stack.  This is expected by
       # multiply & divide.  Because they leave their results in eax
       # associativity works.  Each interim result is pushed on the
@@ -106,9 +112,15 @@ class Compiler
   # Parse and translate a mathematical expression of terms.  Result is
   # in eax.
   def expression
-    term                        # Result is in eax.
+    if addop?
+      # Clear eax simulating a zero before unary plus and minus
+      # operations.
+      emit("xor eax, eax")
+    else
+      term                      # Result is in eax.
+    end
 
-    while ['+', '-'].include?(@look)
+    while addop?
       # Stash the 1st term on the stack.  This is expected by add &
       # subtract.  Because they leave their results in eax
       # associativity works.  Each interim result is pushed on the
@@ -163,4 +175,12 @@ class Compiler
   def eof?
     @input.eof? && @look.nil?
   end
+
+  def addop?
+    @look == '+' || @look == '-'
+  end
+
+  def mulop?
+    @look == '*' || @look == '/'
+  end
 end