Testcase for packrat behaviour

extra/peg/peg-tests.factor

@@ -158,3 +158,23 @@ IN: peg.tests
   "a]" "[" token hide "a" token "]" token hide 3array seq parse 
 ] unit-test
 
+
+{ V{ "1" "-" "1" } V{ "1" "+" "1" } } [
+  [
+    [ "1" token , "-" token , "1" token , ] seq* ,
+    [ "1" token , "+" token , "1" token , ] seq* ,
+  ] choice* 
+  "1-1" over parse parse-result-ast swap
+  "1+1" swap parse parse-result-ast
+] unit-test
+
+{ V{ "1" "-" "1" } V{ "1" "+" "1" } } [
+  [ 
+    [
+      [ "1" token , "-" token , "1" token , ] seq* ,
+      [ "1" token , "+" token , "1" token , ] seq* ,
+    ] choice* 
+    "1-1" over parse parse-result-ast swap
+    "1+1" swap parse parse-result-ast
+  ] with-packrat
+] unit-test

extra/peg/peg.factor

@@ -29,12 +29,22 @@ GENERIC: (compile) ( parser -- quot )
   #! input slice is based on.
   dup slice? [ slice-from ] [ drop 0 ] if ;
 
+: input-cache ( quot cache -- cache )
+  #! From the packrat cache, obtain the cache for the parser quotation 
+  #! that maps the input string position to the parser result.
+  [ drop H{ } clone ] cache ;
+
+: cached-result ( n input-cache input quot -- result )
+  #! Get the cached result for input position n
+  #! from the input cache. If the item is not in the cache,
+  #! call 'quot' with 'input' on the stack to get the result
+  #! and store that in the cache and return it.
+  [ nip ] swap compose curry cache ; inline
+
 :: run-packrat-parser ( input quot c -- result )
   input input-from
-  quot c [ drop H{ } clone ] cache 
+  quot c input-cache 
-  [
+  input quot cached-result ; inline
-    drop input quot call  
-  ] cache ; inline
 
 : run-parser ( input quot -- result )
   #! If a packrat cache is available, use memoization for