Logical "||" operator.

.gitignore

@@ -2,4 +2,5 @@
 build/
 
 # XCode user-specific stuff.
-xcuserdata/
+xcuserdata/
+*.xccheckout

src/compiler.c

@@ -32,6 +32,7 @@ typedef enum
   TOKEN_PLUS,
   TOKEN_MINUS,
   TOKEN_PIPE,
+  TOKEN_PIPEPIPE,
   TOKEN_AMP,
   TOKEN_AMPAMP,
   TOKEN_BANG,
@@ -384,7 +385,18 @@ static void readRawToken(Parser* parser)
         }
         return;
 
-      case '|': makeToken(parser, TOKEN_PIPE); return;
+      case '|':
+        if (peekChar(parser) == '|')
+        {
+          nextChar(parser);
+          makeToken(parser, TOKEN_PIPEPIPE);
+        }
+        else
+        {
+          makeToken(parser, TOKEN_PIPE);
+        }
+        return;
+
       case '&':
         if (peekChar(parser) == '&')
         {
@@ -512,6 +524,7 @@ static void nextToken(Parser* parser)
       case TOKEN_PLUS:
       case TOKEN_MINUS:
       case TOKEN_PIPE:
+      case TOKEN_PIPEPIPE:
       case TOKEN_AMP:
       case TOKEN_AMPAMP:
       case TOKEN_BANG:
@@ -1000,6 +1013,17 @@ void and(Compiler* compiler, int allowAssignment)
   patchJump(compiler, jump);
 }
 
+void or(Compiler* compiler, int allowAssignment)
+{
+  // Skip the right argument if the left is true.
+  emit(compiler, CODE_OR);
+  int jump = emit(compiler, 255);
+
+  parsePrecedence(compiler, 0, PREC_LOGIC);
+
+  patchJump(compiler, jump);
+}
+
 void infixOp(Compiler* compiler, int allowAssignment)
 {
   GrammarRule* rule = &rules[compiler->parser->previous.type];
@@ -1073,6 +1097,7 @@ GrammarRule rules[] =
   /* TOKEN_PLUS          */ INFIX_OPERATOR(PREC_TERM, "+ "),
   /* TOKEN_MINUS         */ OPERATOR(PREC_TERM, "- "),
   /* TOKEN_PIPE          */ UNUSED,
+  /* TOKEN_PIPEPIPE      */ INFIX(PREC_LOGIC, or),
   /* TOKEN_AMP           */ UNUSED,
   /* TOKEN_AMPAMP        */ INFIX(PREC_LOGIC, and),
   /* TOKEN_BANG          */ PREFIX_OPERATOR("!"),

src/vm.c

@@ -577,6 +577,14 @@ int dumpInstruction(VM* vm, ObjFn* fn, int i)
       break;
     }
 
+    case CODE_OR:
+    {
+      int offset = bytecode[i++];
+      printf("OR %d\n", offset);
+      printf("%04d   | offset %d\n", i, offset);
+      break;
+    }
+
     case CODE_IS:
       printf("CODE_IS\n");
       break;
@@ -908,6 +916,25 @@ Value interpret(VM* vm, ObjFn* fn)
         break;
       }
 
+      case CODE_OR:
+      {
+        int offset = READ_ARG();
+        Value condition = PEEK();
+
+        // False is the only falsey value.
+        if (IS_FALSE(condition))
+        {
+          // Discard the condition and evaluate the right hand side.
+          POP();
+        }
+        else
+        {
+          // Short-circuit the right hand side.
+          ip += offset;
+        }
+        break;
+      }
+
       case CODE_IS:
       {
         Value classObj = POP();

src/vm.h

@@ -83,6 +83,10 @@ typedef enum
   // continue.
   CODE_AND,
 
+  // If the top of the stack is non-false, jump [arg] forward. Otherwise, pop
+  // and continue.
+  CODE_OR,
+
   // Pop [a] then [b] and push true if [b] is an instance of [a].
   CODE_IS,
 

test/and.wren

@@ -18,3 +18,9 @@ io.write(true) && // expect: true
 // Swallow a trailing newline.
 io.write(true &&
     true) // expect: true
+
+// Only false is falsy.
+io.write(0 && true) // expect: true
+io.write(null && true) // expect: true
+io.write("" && true) // expect: true
+io.write(false && true) // expect: false

test/if.wren

@@ -44,3 +44,8 @@ if (true) class Foo {} // no error
 // Definition in else arm.
 if (false) null else var a = io.write("ok") // expect: ok
 if (true) null else class Foo {} // no error
+
+// Only false is falsy.
+if (0) io.write(0) // expect: 0
+if (null) io.write(null) // expect: null
+if ("") io.write("empty") // expect: empty

test/or.wren

@@ -0,0 +1,26 @@
+// Note: These tests implicitly depend on ints being truthy.
+//       Also rely on io.write() returning its argument.
+
+// Return the first true argument.
+io.write(1 || true) // expect: 1
+io.write(false || 1) // expect: 1
+io.write(false || false || true) // expect: true
+
+// Return the last argument if all are false.
+io.write(false || false) // expect: false
+io.write(false || false || false) // expect: false
+
+// Short-circuit at the first true argument.
+io.write(false) || // expect: false
+    io.write(true) || // expect: true
+    io.write(true) // should not print
+
+// Swallow a trailing newline.
+io.write(true ||
+    true) // expect: true
+
+// Only false is falsy.
+io.write(0 || true) // expect: 0
+io.write(null || true) // expect: null
+io.write(("" || true) == "") // expect: true
+io.write(false || true) // expect: true