[lazy] added (optional) detection of conditional test of LazySeq, build with:

ant -Dclojure.assert-if-lazy-seq=true
patch from Chouser

Author: richhickey

build.xml

@@ -11,6 +11,7 @@
   <property name="build" location="classes"/>
   <property name="clojure_jar" location="clojure.jar"/>
   <property name="slim_jar" location="clojure-slim.jar"/>
+  <property name="clojure.assert-if-lazy-seq" value=""/>
 
   <target name="init" depends="clean">
     <tstamp/>
@@ -28,6 +29,7 @@
     <java classname="clojure.lang.Compile"
           classpath="${build}:${cljsrc}">
       <sysproperty key="clojure.compile.path" value="${build}"/>
+      <sysproperty key="clojure.assert-if-lazy-seq" value="${clojure.assert-if-lazy-seq}"/>
       <arg value="clojure.core"/>
       <arg value="clojure.main"/>
       <arg value="clojure.set"/>

src/clj/clojure/core.clj

@@ -35,6 +35,10 @@
  #^{:macro true}
  fn (fn* fn [& decl] (cons 'fn* decl)))
 
+(def
+ #^{:macro true}
+ if (fn* if [& decl] (cons 'if* decl)))
+
 (def
  #^{:arglists '([coll])
     :doc "Returns the first item in the collection. Calls seq on its
@@ -291,6 +295,20 @@
 
 (. (var defmacro) (setMacro))
 
+(defmacro assert-if-lazy-seq? {:private true} []
+  (let [prop (System/getProperty "clojure.assert-if-lazy-seq")]
+    (if prop
+      (if (clojure.lang.Util/equals prop "") nil true))))
+
+(defmacro if [tst & etc]
+  (if* (assert-if-lazy-seq?)
+    (let [tstsym 'G__0_0]
+      (list 'let [tstsym tst]
+	(list 'if* (list 'clojure.core/instance? clojure.lang.LazySeq tstsym)
+           (list 'throw (list 'new Exception "LazySeq used in 'if'"))
+	   (cons 'if* (cons tstsym etc)))))
+    (cons 'if* (cons tst etc))))
+
 (defmacro when
   "Evaluates test. If logical true, evaluates body in an implicit do."
   [test & body]
@@ -1642,7 +1660,7 @@
   ([coll]
    (sort compare coll))
   ([#^java.util.Comparator comp coll]
-   (when (and coll (not (zero? (count coll))))
+   (when (seq coll)
      (let [a (to-array coll)]
        (. java.util.Arrays (sort a comp))
        (seq a)))))

src/clj/clojure/core_proxy.clj

@@ -155,7 +155,7 @@
                              meths (concat 
                                     (seq (. c (getDeclaredMethods)))
                                     (seq (. c (getMethods))))]
-                        (if meths 
+                        (if (seq meths)
                           (let [#^java.lang.reflect.Method meth (first meths)
                                 mods (. meth (getModifiers))
                                 mk (method-sig meth)]

src/jvm/clojure/lang/Compiler.java

@@ -40,7 +40,7 @@ public class Compiler implements Opcodes{
 static final Symbol DEF = Symbol.create("def");
 static final Symbol LOOP = Symbol.create("loop*");
 static final Symbol RECUR = Symbol.create("recur");
-static final Symbol IF = Symbol.create("if");
+static final Symbol IF = Symbol.create("if*");
 static final Symbol LET = Symbol.create("let*");
 static final Symbol DO = Symbol.create("do");
 static final Symbol FN = Symbol.create("fn*");