Interpret cond; allow else in cond & match

src/ludus/interpreter.clj

@@ -109,6 +109,23 @@
             (recur (first clauses) (rest clauses))))
         (throw (ex-info "Match Error: No match found" {}))))))
 
+(defn- interpret-cond [ast ctx]
+  (let [clauses (:clauses ast)]
+    (loop [clause (first clauses)
+      clauses (rest clauses)]
+      (if (not clause)
+        (throw (ex-info "Cond Error: No match found" {}))
+        (let [test-expr (:test clause)
+          body (:body clause)
+          truthy? (boolean (interpret-ast test-expr ctx))]
+          (if truthy?
+            (interpret-ast body ctx)
+            (recur (first clauses) (rest clauses))
+            )
+          )
+        )
+      )))
+
 (defn- interpret-called-kw [kw tuple ctx]
   ;; TODO: check this statically
   (if (not (= 1 (:length tuple)))
@@ -228,6 +245,8 @@
 
     ::ast/match (interpret-match ast ctx)
 
+    ::ast/cond (interpret-cond ast ctx)
+
     ::ast/synthetic (interpret-synthetic ast ctx)
 
     ::ast/fn (interpret-fn ast ctx)
@@ -286,10 +305,13 @@
 
   (def source "
 
-    fn square (x) -> mult (x, x)
-
-    let foo = square (_)
+    let foo = 2
 
+    match foo with {
+      1 -> :one
+      2 -> :two
+      else -> :oops
+    }
 
 	")
 

src/ludus/parser.clj

@@ -487,7 +487,9 @@
     (parse-then (accept ::token/newline ast))))
 
 (defn- parse-match-clause [parser]
-  (let [pattern (parse-pattern parser)
+  (let [pattern (if (= ::token/else (token-type parser))
+                  (-> parser (advance) (assoc ::ast {::ast/type ::ast/placeholder}))
+                  (parse-pattern parser))
         rarrow (expect* #{::token/rarrow} "Expected arrow after pattern" pattern)]
     (if (:success rarrow)
       (let [body (parse-expr (:parser rarrow))]
@@ -531,7 +533,13 @@
       (panic parser "Expected with after match expression"))))
 
 (defn- parse-cond-clause [parser]
-  (let [expr (parse-expr parser)
+  (let [expr (if (= ::token/else (token-type parser))
+               (-> parser
+                 (advance)
+                 (assoc ::ast {::ast/type ::ast/atom
+                               :token ::token/else
+                               :value true}))
+               (parse-expr parser))
         rarrow (expect* #{::token/rarrow} "Expected arrow after expression in cond clause" expr)]
     (if (:success rarrow)
       (let [body (parse-expr (:parser rarrow))]
@@ -543,7 +551,6 @@
   (loop [parser (accept-many #{::token/newline} parser)
          clauses []]
     (let [curr (current parser)]
-      (println "parsing a clause: " curr)
       (case (::token/type curr)
         ::token/rbrace
         (if (< 0 (count clauses))        
@@ -562,7 +569,6 @@
         (expect* #{::token/lbrace} "Expected { after cond" (advance parser))]
     (if (:success header)
       (let [clauses (parse-cond-clauses (:parser header))]
-        (println "Found all the clauses")
         (assoc clauses ::ast {::ast/type ::ast/cond
                               :clauses (get-in clauses [::ast :clauses])})
         )
@@ -711,9 +717,12 @@
     (parser)
     (parse-script)))
 
-(do
+(comment
   (def pp pp/pprint)
-  (def source "cond {}
+  (def source "match foo with {
+    1 -> :foo
+    else -> bar
+  }
 
     ")
   (def lexed (scanner/scan source))