Lists of lists

[andreasabel]

Given this .cf file:

Start. S ::= [[E]] ;

Atom. E ::= Integer;
separator E "*"    ;
separator [E] "+"  ;

and this test input:

5 * 8 + 1 * 2 + 1

• The haskell backend seems to produce a correct parser, but the printer drops the separators of the outer list:

happy -gca LL/Par.y
reduce/reduce conflicts: 3

[Abstract Syntax]
Start [[Atom 5,Atom 8],[Atom 1,Atom 2],[Atom 1]]

[Linearized tree]
5 * 8 1 * 2 1

• The haskell-gadt backend cannot produce the abstract syntax:

happy -gca LL/Par.y
reduce/reduce conflicts: 3

[3 of 8] Compiling LL.Abs           ( LL/Abs.hs, LL/Abs.o )

LL/Abs.hs:21:55:
    Couldn't match type ‘Tree a0’ with ‘[E]’
    Expected type: Tree a0 -> m [E]
      Actual type: Tree a0 -> m (Tree a0)
    In the second argument of ‘(.)’, namely ‘f’
    In the second argument of ‘(.)’, namely ‘a (r (:)) . f’

• The java backend cannot produce the abstract syntax:

LL/Absyn/ListListE.java:3: error: illegal start of type
public class ListListE extends java.util.LinkedList<[E]> 

• The c, cpp, and cpp-nostl backends seem to work almost correctly; they seem to flatten lists when debug printing ASTs.

bison -t -pLL LL.y -o Parser.c
LL.y: warning: 2 reduce/reduce conflicts [-Wconflicts-rr]

[Abstract Syntax]
(Start [(Atom 5), (Atom 8), (Atom 1), (Atom 2), (Atom 1)])

[Linearized Tree]
5 * 8 + 1 * 2 + 1

• The ocaml backend can't produce a printer:

ocamlyacc ParLL.mly
1 rule never reduced
3 reduce/reduce conflicts.

ocamlc  -o TestLL BNFC_Util.ml AbsLL.ml SkelLL.ml ShowLL.ml ...
File "ShowLL.ml", line 43, characters 66-74:
Error: This expression has type ('a -> showable) -> 'a list -> showable
       but an expression was expected of type ('a -> showable) -> showable

• The latex backend works correctly.

[andreasabel]

The reduce-reduce conflict seems only to appear at the eof, there are two, however confluent, reduce paths:

eps --> [[E]]
eps --> [E] --> [[E]]

[andreasabel]

An even shorter test case (still avoiding #163) is:

Start. S ::= [[Integer]] ;
separator Integer   "*"  ;
separator [Integer] "+"  ;

Here, the haskell backend drops both levels of separators in the printer.