#+title: Unhappy About Happy: A Reflection or Something Like That
#&summary
Rant about Haskell's parser "Happy".
#&
#+license: wtfpl
#+startup: showall
#&toc

#&img;url=UNHAPPY.PNG,float=right

* Unhappy About Happy: A Reflection or Something Like That

For the purposes of my quiet rage, this document will be written in all caps.
I also will not use proper language.  I won't even give suggestions on how to
improve Happy; I'll just complain.

STARTING NOW


** WHAT HAPPY ???

HAPPY IS PARSER GENERATOR.  IT GENERATE HASKELL CODE.  VISIT
[[http://www.haskell.org/happy/][HTTP://WWW.HASKELL.ORG/HAPPY/]] FOR UGLY INFO.


** HOW HAPPY GOOD

+ EFFICIENT I GUESS
+ WORKS OK
+ PRETTY LOGO


** WHY I NOT LIKE HAPPY

*** JUZT TYPICAL

#+caption: ONE REASON.  TRUST NOT BUSH WITH HAPPY
#&img;url=MEME0.PNG,float=center

ONE ERROR IN PARSER.Y GIVE HUGE TYPE ERROR

*WHAT IS THIS!*


#+BEGIN_SRC
dist/build/l0c/l0c-tmp/Language/L0/Parser/Parser.hs:2452:42:
    Couldn't match type `Value' with `BasicValue -> Value'
    Expected type: HappyAbsSyn
                     (Name, SrcLoc)
                     [(Name,
                       DeclTypeBase Name,
                       [ParamBase Name],
                       ExpBase NoInfo Name,
                       SrcLoc)]
                     (Name,
                      DeclTypeBase Name,
                      [ParamBase Name],
                      ExpBase NoInfo Name,
                      SrcLoc)
                     Uniqueness
                     ([Maybe (DimSize Name)], ElemTypeBase NoInfo Name)
                     (ElemTypeBase NoInfo Name)
                     [TypeBase NoInfo Name]
                     [TypeBase NoInfo Name]
                     [ParamBase Name]
                     (Maybe (CertificatesBase NoInfo Name), [ExpBase NoInfo Name])
                     [ExpBase NoInfo Name]
                     [ExpBase NoInfo Name]
/* ... 200-300 MORE LINES ... */
                        [TupIdentBase NoInfo Name]
                        (TupIdentBase NoInfo Name)
                        (LambdaBase NoInfo Name)
                        (TupleLambdaBase NoInfo Name)
                        (BasicValue -> Value)
                        Int
                        (BasicValue -> Value)
                        (BasicValue -> Value)
                        (BasicValue -> Value)
                        (BasicValue -> Value)
                        (BasicValue -> Value)
                        Value
                        (BasicValue -> Value)
                        (BasicValue -> Value)
                        [Value]
                        [Value]
    In the second argument of `happySpecReduce_3', namely
      `happyReduction_191'
    In the expression: happySpecReduce_3 38# happyReduction_191
    In an equation for `happyReduce_191':
        happyReduce_191 = happySpecReduce_3 38# happyReduction_191
#+END_SRC

*NOT NICE NOT NICE AT ALL*


*** MONADA CAN I HAZ

MAYHAPS U NEED TO PARSE DIFFERENT THAN NORMAL KAY.  HOW U THINK.  YES:
MENTALINCRMENTAL PARSING IT IS

#+caption: TWO REASON (I UNGOOD TO MEMES)
#&img;url=MEME1.PNG,float=center

YOU GOT NEED TO PARSE IO GETLINE SOURCES YEAH

PARSE EXPRESSION "2 + 1 *4" OVER MULTI LINES LIKE THIS HERE

#+BEGIN_SRC
WELCOM TO DA FUNKY MULTILINE EXPRESSION PARSER; ENTER UR EXPRESSION
> 2 +
1 *4
TY GOT IT!!  PARSED EXPRESSION IS "2 + 1 * 4" AND U NICE; RESULT IS 6 BTW
>
#+END_SRC

PARSER SHOULD KNOW "YEAH NOT DUHNE PARSIN YET" WHEN "2 +" READ, SHOULD TEHN
READ NEW LINE AND PARSE MORE!

WE CAN PARSE FROM BEGINNING EVERY TIME SURE BUT INEFECICIENT!!!

#+caption: WE NOT WANT TIS SAYS PICARD 8-)
#&img;url=MEME2.PNG,float=center

BUT HOW WE SHOULD / COULD DO THAT SMARTLY I IMPLORE TO LIKE ASK U

#+caption: CLEVER GILES HAS OUR SOLUTION!!!!!
#&img;url=MEME3.PNG,float=center

YES WE USE CONTINUATION WHICH SMART.  LOOK ATTOPARSEC USE CONTINUATION IN
RETURN!
[[http://hackage.haskell.org/package/attoparsec-0.11.1.0/docs/Data-Attoparsec-Text.html#t:IResult][HTTP://HACKAGE.HASKELL.ORG/PACKAGE/ATTOPARSEC-0.11.1.0/DOCS/DATA-ATTOPARSEC-TEXT.HTML#T:IRESULT]]

YEAH BUT NOT IN HAPPY............

SO WE MAKE IT MANUAL.  WE SPECIFY OWN LEXER AND IMPROVE MONAD.  WHEN END OF
LINE IS REACH, WE TELL PARSER (FROM INSIDE DA PRASER) DAT DERE IS NO MORE EVER;
IF THAT FAILS WE CATCH ERROR (EITHER-LIKE MONAD) AND READ NEW LINE FOR REALS

#+caption: AS MANY LINES AS LE POSSIBLÉ
#&img;url=MEME4.PNG,float=center

CLEVER SOLUTION OF US!  BUT IN PARSE EXPRESION EXAMPLE ABOV WE USE IO TO GETLINE

*WE NOT WANT IO IN ALL PARSING.... EVER EVER!!!!!!!!*

HOWTO ABSTRACT IO AWAY?  WE WANT TYPE OF EXPORTED FUNCTIONS FROM PARSER TO NOT
USE _IO_ /AT ALL/

#+caption: YAEH BABBY
#&img;url=MEME5.PNG,float=center

SO WE USE WHATEVER MONAD TO GETLINE RIGHT?

#+BEGIN_SRC haskell
class GetLiner m where -- KAY SO m IS MONAD RIGHT
  getSomeLine :: m String

instance GetLiner IO where
  getSomeLine = getLine
#+END_SRC

WAIT I DONT GET IT

#+BEGIN_SRC haskell
CLASS GETLINER M WHERE -- KAY SO M IS MONAD RIGHT
  GETSOMELINE :: M STRING

INSTANCE GETLINER IO WHERE
  GETSOMELINE = GETLINE
#+END_SRC

MUCH BETTR.  COZ TEHN WE CAN USE

#+caption: ... THEN WAT.  Y U SO SLACK
#&img;url=MEME6.PNG,float=center

BUT YIAH WE COULD USE TYPE CONSTRAINTS!

#+BEGIN_SRC haskell
LEXER :: GETLINER M => M SOMETHNIG
LEXER = MEHMEHMEH
  WOO <- GETSOMELINE
  MEH MEH
#+END_SRC

SURE COULD WORK WE NEED JUST TELL HAPPY BOUT IT.

#+BEGIN_SRC
%MONAD { GETLINER M => SOMETHINNG M }
#+END_SRC

FAILS MISERBLY.................... :-( :( :(

WE ARE LEFT 4 PONDER HOW TO SOLVE!  HOWTO ABSTRAKT OUT IO!  HOW!!

#+caption: TRANCEND CONVENTIONAL COMPUTATIN U CAPITALIS PIG
#&img;url=MEME7.PNG,float=center

SOOOO..... WE NEED KINDA CONTINUATIN COMPUTATON MONADY THINGY.  I GOT FRIEND
WHO COME WIT CODE, SAY IT GOOD CODE.  I CHECK, HE RIGHT!  IS HERE

#+BEGIN_SRC haskell
DATA READLINEMONAD A = VALUE A
                     | GETLINE (STRING -> READLINEMONAD A)

INSTANCE MONAD READLINEMONAD WHERE
  RETURN = VALUE
  VALUE X >>= F = F X
  GETLINE G >>= F = GETLINE $ \S -> G S >>= F
#+END_SRC

HA CLEVER!!!  NOW WE NEED NO TYPE CONSTRAINTS BECAUSE NOW COMPUTATION IS MONAD
ITSELF!  HOW YOU ASK.

READLINEMONAD HAS NO IO OR ANY ELSE BUILTIN; IT GETS LINE BY CREATE FUNCTION
WHICH TAKES LINE TO CONTINUU EXECUTION.  AGAIN AND AGAIN!  LINE CAN COME FROM
ANYTHIN.

EXAMPLE FOR USING RESULT!
#+BEGIN_SRC haskell
GETLINESFROMIO :: READLINEMONAD A -> IO A
GETLINESFROMIO (VALUE X) = RETURN X
GETLINESFROMIO (GETLINE F) = DO
  S <- GETLINE
  GETLINESFROMIO $ F S
#+END_SRC

U SEE WAT GOIN ON DERE!  IN OUR LEXER WE NAMELI USED
#+BEGIN_SRC haskell
GETLINE VALUE
#+END_SRC

TO GET LINE (BECAUSE FITS WITH CLEVER MONAD!)

*NICE-O!*


** CODE IN QUSTION

LOOKIE HER FOR FULL DETAILS (ALTHOU WITH NO FULL CAPS):
[[https://raw.github.com/HIPERFIT/L0Language/master/src/Language/L0/Parser/Parser.y][HTTPS://RARRW.GITHUB.COM/HIPERFIT/L0LANGUAGE/MASTER/SRC/LANGUAGE/L0/PARSER/PARSER.Y]]


** CONCLUSION

#+caption: TRU STORY
#&img;url=MEME8.PNG,float=center

#+caption: NOT ME
#&img;url=MEME9.PNG,float=center

THIS IS ENTRELY OBJECTIVE.

THIS IS ENTIREY OBJECTIVE.

THIS IS ENTIRLY OBJECTIVE.