diff --git a/TODO.xit b/TODO.xit
index 114eed8..5b5d164 100644
--- a/TODO.xit
+++ b/TODO.xit
@@ -21,7 +21,7 @@ Finish interpreter
 [ ] Merge new interpreter
 
 Write a compiler: desugaring
-[ ] `...` to `..._` in tuple & list patterns
+[~] `...` to `..._` in tuple & list patterns
 [ ] placeholder partial application to anonymous lambda
 [ ] word -> :[word] word in pairs (patterns & expressions)
 
@@ -31,10 +31,10 @@ Write a compiler: correctness
 [ ] check that recur is in tail position
 [ ] check that recur is only called inside loop or fn forms
 [ ] check ns accesses
+[ ] prevent import cycles
 [ ] splattern is last member in a pattern
 [ ] -----List/Tuple
 [ ] -----Dict/Struct/Set
-[ ] prevent import cycles
 
 Write a compiler: optimization
 [ ] devise tail call optimization
diff --git a/src/ludus/grammar.clj b/src/ludus/grammar.clj
index 644c71d..52a6cd9 100644
--- a/src/ludus/grammar.clj
+++ b/src/ludus/grammar.clj
@@ -4,35 +4,25 @@
 
 (declare expression pattern)
 
-;(def separator (choice :separator [:comma :newline :break]))
 (defp separator choice [:comma :newline :break])
 
-;(def separators (quiet (one+ separator)))
 (defp separators quiet one+ separator)
 
-;(def terminator (choice :terminator [:newline :semicolon :break]))
 (defp terminator choice [:newline :semicolon :break])
 
-;(def terminators (quiet (one+ terminator)))
 (defp terminators quiet one+ terminator)
 
-;(def nls? (quiet (zero+ :nls :newline)))
 (defp nls? quiet zero+ :newline)
 
-;(def splat (group (order-1 :splat [(quiet :splat) :word])))
 (defp splat group order-1 [(quiet :splat) :word])
 
-;(def splattern (group (order-1 :splat [(quiet :splat) (maybe (flat (choice :splatted [:word :ignored :placeholder])))])))
 (defp patt-splat-able flat choice [:word :ignored :placeholder])
 (defp splattern group order-1 [(quiet :splat) (maybe patt-splat-able)])
 
-;(def literal (flat (choice :literal [:nil :true :false :number :string])))
 (defp literal flat choice [:nil :true :false :number :string])
 
-;(def tuple-pattern-term (flat (choice :tuple-pattern-term [pattern splattern])))
 (defp tuple-pattern-term flat choice [pattern splattern])
 
-;(def tuple-pattern-entry (weak-order :tuple-pattern-entry [tuple-pattern-term separators]))
 (defp tuple-pattern-entry weak-order [tuple-pattern-term separators])
 
 (defp tuple-pattern group order-1 [(quiet :lparen)
@@ -65,29 +55,30 @@
                                    	(quiet :rbrace)
                                    	])
 
-(defp guard order-0 [(quiet :when) expression])
+(defp guard order-0 [(quiet :if) expression])
 
 (defp pattern flat choice [literal 
                            :ignored 
                            :placeholder 
                            typed 
                            :word 
-                           :keyword 
+                           :keyword
+                           :else 
                            tuple-pattern 
                            dict-pattern 
                            struct-pattern 
                            list-pattern])
 
-(defp match-clause group weak-order :match-clause [pattern (maybe guard) (quiet :rarrow) expression])
+(defp match-clause group weak-order [pattern (maybe guard) (quiet :rarrow) expression])
 
 (defp match-entry weak-order [match-clause terminators])
 
-(defp match group order-1 [(quiet :match) expression nls? 
-                          	(quiet :with) (quiet :lbrace)
-                          	(quiet (zero+ terminator))
-                          	(one+ match-entry)
-                          	(quiet :rbrace)
-                          	])
+(defp match-old group order-1 [(quiet :match) expression nls? 
+                              	(quiet :with) (quiet :lbrace)
+                              	(quiet (zero+ terminator))
+                              	(one+ match-entry)
+                              	(quiet :rbrace)
+                              	])
 
 (defp if-expr group order-1 [(quiet :if) 
                              nls? 
@@ -105,11 +96,26 @@
 
 (defp cond-entry weak-order [cond-clause terminators])
 
-(defp cond-expr group order-1 [(quiet :cond) (quiet :lbrace)
+(defp cond-old group order-1 [(quiet :cond) (quiet :lbrace)
+                              (quiet (zero+ terminator))
+                              (one+ cond-entry)
+                              (quiet :rbrace)])
+
+(defp match group order-1 [expression nls? 
+                           (quiet :is) (quiet :lbrace)
+                           (quiet (zero+ terminator))
+                           (one+ match-entry)
+                           (quiet :rbrace)])
+
+(defp cond-expr group order-1 [(quiet :lbrace)
                                (quiet (zero+ terminator))
                                (one+ cond-entry)
                                (quiet :rbrace)])
 
+(defp when-tail flat choice [match cond-expr])
+
+(defp when-expr weak-order [(quiet :when) when-tail])
+
 (defp let-expr group order-1 [(quiet :let)
                              	pattern
                              	(quiet :equals)
@@ -229,11 +235,12 @@
                               	(flat (choice :loop-body [fn-clause compound-loop]))])
 
 (defp expression flat choice [fn-expr
-                             	match
+                             	;match
                              	loop-expr
                              	let-expr
                              	if-expr 
-                             	cond-expr
+                             	;cond-expr
+                              when-expr
                              	spawn
                              	receive
                              	synthetic
diff --git a/src/ludus/interpreter.clj b/src/ludus/interpreter.clj
index 0ff06d1..4ccdfc9 100644
--- a/src/ludus/interpreter.clj
+++ b/src/ludus/interpreter.clj
@@ -275,7 +275,7 @@
   ;(println "Matching " value " with pattern type " (:type pattern))
   (let [ctx @ctx-vol]
     (case (:type pattern)
-      (:placeholder :ignored)
+      (:placeholder :ignored :else)
       {:success true :ctx {}}
 
       (:number :nil :true :false :string :keyword)
@@ -843,6 +843,8 @@
 
     :ref-expr (interpret-ref ast ctx)
 
+    :when-expr (interpret-ast (-> ast :data first) ctx)
+
     ; ::ast/spawn (interpret-spawn ast ctx)
 
     ; ::ast/receive (interpret-receive ast ctx)
@@ -961,8 +963,11 @@
 
 (do
   (def source "
-    let @{...x} = @{:a 1, :b 2, :c 3}
-    x
+    let x = (1, 2)
+    when x is {
+      (y, 2) if eq (y, 1) -> :onetwo
+      _ -> :not_x
+    }
       ")
 
   (println "")
diff --git a/src/ludus/interpreter_new.clj b/src/ludus/interpreter_new.clj
index 3c7c268..2a5815e 100644
--- a/src/ludus/interpreter_new.clj
+++ b/src/ludus/interpreter_new.clj
@@ -5,13 +5,13 @@
   		[ludus.scanner :as s]))
 
 (def source 
-  "#{a as :number}
+  "when x is { true -> true }
 "
   )
 
 (def tokens (-> source s/scan :tokens))
 
-(def result (p/apply-parser g/dict-pattern tokens))	
+(def result (p/apply-parser g/when-expr tokens))	
 
 (-> result :data) 
 
diff --git a/src/ludus/scanner.clj b/src/ludus/scanner.clj
index a4c5ea8..368da41 100644
--- a/src/ludus/scanner.clj
+++ b/src/ludus/scanner.clj
@@ -8,7 +8,7 @@
   "List of Ludus reserved words."
   ;; see ludus-spec repo for more info
   {"as" :as ;; impl for `import`; not yet for patterns
-   "cond" :cond ;; impl
+   ;"cond" :cond ;; impl
    "do" :do ;; impl
    "else" :else ;; impl
    "false" :false ;; impl -> literal word
@@ -17,7 +17,7 @@
    "import" :import ;; impl
    "let" :let ;; impl
    "loop" :loop ;; impl
-   "match" :match ;; impl
+   ; "match" :match ;; impl
    "nil" :nil ;; impl -> literal word
    "ns" :ns ;; impl
    ;; "panic!" :panic ;; impl (should be a function)
@@ -25,7 +25,7 @@
    "ref" :ref ;; impl
    "then" :then ;; impl
    "true" :true ;; impl -> literal word
-   "with" :with ;; impl
+   ;"with" :with ;; impl
 
    ;; actor model/concurrency
    "receive" :receive
@@ -40,6 +40,7 @@
    "test" :test
    "when" :when
    ;; "module" :module ;; not necessary if we don't have datatypes
+   "is" :is
    })
 
 (def literal-words {