Add tests for left recusion in pegs

extra/peg/ebnf/ebnf-tests.factor

@@ -143,3 +143,31 @@ IN: peg.ebnf.tests
 { f } [
   "Z" [EBNF foo=[^A-Z] EBNF] call  
 ] unit-test
+
+[ 
+  #! Test direct left recursion. Currently left recursion should cause a
+  #! failure of that parser.
+  #! Not using packrat, so recursion causes data stack overflow  
+  "1+1" [EBNF num=([0-9])+ expr=expr "+" num | num EBNF] call
+] must-fail
+
+{ V{ 49 } } [ 
+  #! Test direct left recursion. Currently left recursion should cause a
+  #! failure of that parser.
+  #! Using packrat, so first part of expr fails, causing 2nd choice to be used  
+  "1+1" [ [EBNF num=([0-9])+ expr=expr "+" num | num EBNF] call ] with-packrat parse-result-ast
+] unit-test
+
+[ 
+  #! Test indirect left recursion. Currently left recursion should cause a
+  #! failure of that parser.
+  #! Not using packrat, so recursion causes data stack overflow  
+  "1+1" [EBNF num=([0-9])+ x=expr expr=x "+" num | num EBNF] call
+] must-fail
+
+{ V{ 49 } } [ 
+  #! Test indirect left recursion. Currently left recursion should cause a
+  #! failure of that parser.
+  #! Using packrat, so first part of expr fails, causing 2nd choice to be used  
+  "1+1" [ [EBNF num=([0-9])+ x=expr expr=x "+" num | num EBNF] call ] with-packrat parse-result-ast
+] unit-test

extra/peg/ebnf/ebnf.factor

@@ -266,7 +266,7 @@ M: ebnf-non-terminal (transform) ( ast -- parser )
   ] [ ] make delay sp ;
 
 : transform-ebnf ( string -- object )
-  'ebnf' parse parse-result-ast transform ;
+  'ebnf' [ parse ] packrat-parse parse-result-ast transform ;
 
 : check-parse-result ( result -- result )
   dup [
@@ -281,7 +281,7 @@ M: ebnf-non-terminal (transform) ( ast -- parser )
   ] if ;
 
 : ebnf>quot ( string -- hashtable quot )
-  'ebnf' parse check-parse-result 
+  'ebnf' [ parse ] with-packrat check-parse-result 
   parse-result-ast transform dup main swap at compile 1quotation ;
 
 : [EBNF "EBNF]" parse-multiline-string ebnf>quot nip parsed ; parsing

extra/peg/peg-tests.factor

@@ -180,3 +180,19 @@ IN: peg.tests
     "1+1" swap parse parse-result-ast
   ] with-packrat 
 ] unit-test
+
+: expr ( -- parser ) 
+  #! Test direct left recursion. Currently left recursion should cause a
+  #! failure of that parser.
+  [ expr ] delay "+" token "1" token 3seq "1" token 2choice ;
+
+[
+  #! Not using packrat, so recursion causes data stack overflow  
+  "1+1" expr parse parse-result-ast   
+] must-fail
+
+{ "1" } [
+  #! Using packrat, so expr fails, causing the 2nd choice to be used.  
+  "1+1" expr [ parse ] with-packrat parse-result-ast   
+] unit-test
+

extra/peg/peg.factor

@@ -39,7 +39,11 @@ GENERIC: (compile) ( parser -- quot )
   #! 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.
-  n input-cache [ drop input quot call ] cache ; inline
+  n input-cache [ 
+    drop
+    f n input-cache set-at
+    input quot call 
+  ] cache ; inline
 
 :: run-packrat-parser ( input quot c -- result )
   input input-from