From b53da9531cf3021d8585ef1bc1ab5434cf780543 Mon Sep 17 00:00:00 2001
From: Brian Picciano <mediocregopher@gmail.com>
Date: Sun, 24 Jul 2016 15:04:06 -0600
Subject: [PATCH] implement expr.Macro

---
 expr/expr.go      | 28 ++++++++++++++++++++++++++--
 expr/expr_test.go |  5 +++++
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/expr/expr.go b/expr/expr.go
index 914bbb6..bddb928 100644
--- a/expr/expr.go
+++ b/expr/expr.go
@@ -90,6 +90,27 @@ func (id Identifier) Equal(e Actual) bool {
 
 ////////////////////////////////////////////////////////////////////////////////
 
+// Macro is an identifier for a macro which can be used to transform
+// expressions. The tokens for macros start with a '%', but the Macro identifier
+// itself has that stripped off
+type Macro string
+
+// String returns the Macro with a '%' prepended to it
+func (m Macro) String() string {
+	return "%" + string(m)
+}
+
+// Equal implements the Actual method
+func (m Macro) Equal(e Actual) bool {
+	mm, ok := e.(Macro)
+	if !ok {
+		return false
+	}
+	return m == mm
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
 // Tuple represents a fixed set of expressions which are interacted with as if
 // they were a single value
 type Tuple []Expr
@@ -391,12 +412,15 @@ func parseIdentifier(t lexer.Token) (Expr, error) {
 		}
 		e.Actual = Int(n)
 
-	} else if t.Val == "true" {
+	} else if t.Val == "%true" {
 		e.Actual = Bool(true)
 
-	} else if t.Val == "false" {
+	} else if t.Val == "%false" {
 		e.Actual = Bool(false)
 
+	} else if t.Val[0] == '%' {
+		e.Actual = Macro(t.Val[1:])
+
 	} else {
 		e.Actual = Identifier(t.Val)
 	}
diff --git a/expr/expr_test.go b/expr/expr_test.go
index 9019702..f377e9d 100644
--- a/expr/expr_test.go
+++ b/expr/expr_test.go
@@ -43,7 +43,9 @@ func assertParse(t *T, in []lexer.Token, expExpr Expr, expOut []lexer.Token) {
 
 func TestParseSingle(t *T) {
 	foo := lexer.Token{TokenType: lexer.Identifier, Val: "foo"}
+	fooM := lexer.Token{TokenType: lexer.Identifier, Val: "%foo"}
 	fooExpr := Expr{Actual: Identifier("foo")}
+	fooMExpr := Expr{Actual: Macro("foo")}
 
 	toks := []lexer.Token{foo}
 	assertParse(t, toks, fooExpr, []lexer.Token{})
@@ -56,6 +58,9 @@ func TestParseSingle(t *T) {
 
 	toks = []lexer.Token{openParen, openParen, foo, closeParen, closeParen, foo}
 	assertParse(t, toks, fooExpr, []lexer.Token{foo})
+
+	toks = []lexer.Token{fooM, foo}
+	assertParse(t, toks, fooMExpr, []lexer.Token{foo})
 }
 
 func TestParseTuple(t *T) {