Spread now infers with the correct stack effect. Make spread>quot-shallow which trims empty quotations off the head of the spread sequence. Fixes #139.

basis/fry/fry.factor

@@ -95,7 +95,7 @@ INSTANCE: fried-callable fried
     check-fry mark-composes
     { _ } split convert-curries
     [ [ [ ] ] [ [ ] (make-curry) but-last ] if-zero ]
-    [ spread>quot swap [ [ ] (make-curry) compose ] unless-zero ] if-empty ;
+    [ spread>quot-shallow swap [ [ ] (make-curry) compose ] unless-zero ] if-empty ;
 
 DEFER: dredge-fry
 

core/classes/tuple/tuple.factor

@@ -134,7 +134,7 @@ M: class final-class? drop t ;
     superclasses [ "slots" word-prop length ] map-sum ;
 
 : boa-check-quot ( class -- quot )
-    all-slots [ class>> instance-check-quot ] map spread>quot
+    all-slots [ class>> instance-check-quot ] map spread>quot-shallow
     f like ;
 
 : define-boa-check ( class -- )

core/combinators/combinators-tests.factor

@@ -1,6 +1,6 @@
 USING: alien strings kernel math tools.test io prettyprint
 namespaces combinators words classes sequences accessors
-math.functions arrays combinators.private ;
+math.functions arrays combinators.private stack-checker ;
 IN: combinators.tests
 
 [ 3 ] [ 1 2 [ + ] call( x y -- z ) ] unit-test
@@ -320,3 +320,7 @@ DEFER: corner-case-1
 
 [ "nachos" ] [ 33 test-case-12 ] unit-test
 [ "nachos" ] [ 33 \ test-case-12 def>> call ] unit-test
+
+[ (( x x -- x x )) ] [
+    [ { [ ] [ ] } spread ] infer
+] unit-test

core/combinators/combinators.factor

@@ -65,9 +65,12 @@ SLOT: terminated?
     [ [ 3keep ] curry ] map concat [ 3drop ] append [ ] like ;
 
 ! spread
-: spread>quot ( seq -- quot )
+: spread>quot-shallow ( seq -- quot )
     [ ] [ [ dup empty? [ [ dip ] curry ] unless ] dip append ] reduce ;
 
+: spread>quot ( seq -- quot )
+    [ ] [ [ [ dip ] curry ] dip append ] reduce ;
+
 : spread ( objs... seq -- )
     spread>quot call ;