244 lines
6.5 KiB
Markdown
244 lines
6.5 KiB
Markdown
---
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abstract: Rant about Haskell's parser "Happy".
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lastupdated: 2014
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---
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# Unhappy About Happy: A Reflection or Something Like That
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*2014.*
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For the purposes of my quiet rage, this document will be written in all
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caps. I also will not use proper language. I won't even give suggestions
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on how to improve Happy; I'll just complain.
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STARTING NOW
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WHAT HAPPY ???
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--------------
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HAPPY IS PARSER GENERATOR. IT GENERATE HASKELL CODE. VISIT
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[<HTTP://WWW.HASKELL.ORG/HAPPY/>](http://www.haskell.org/happy/) FOR
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UGLY INFO.
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HOW HAPPY GOOD
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--------------
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- EFFICIENT I GUESS
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- WORKS OK
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- PRETTY LOGO
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WHY I NOT LIKE HAPPY
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--------------------
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### JUZT TYPICAL
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ONE ERROR IN PARSER.Y GIVE HUGE TYPE ERROR
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**WHAT IS THIS!**
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dist/build/l0c/l0c-tmp/Language/L0/Parser/Parser.hs:2452:42:
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Couldn't match type `Value' with `BasicValue -> Value'
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Expected type: HappyAbsSyn
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(Name, SrcLoc)
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[(Name,
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DeclTypeBase Name,
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[ParamBase Name],
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ExpBase NoInfo Name,
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SrcLoc)]
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(Name,
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DeclTypeBase Name,
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[ParamBase Name],
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ExpBase NoInfo Name,
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SrcLoc)
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Uniqueness
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([Maybe (DimSize Name)], ElemTypeBase NoInfo Name)
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(ElemTypeBase NoInfo Name)
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[TypeBase NoInfo Name]
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[TypeBase NoInfo Name]
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[ParamBase Name]
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(Maybe (CertificatesBase NoInfo Name), [ExpBase NoInfo Name])
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[ExpBase NoInfo Name]
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[ExpBase NoInfo Name]
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/* ... 200-300 MORE LINES ... */
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[TupIdentBase NoInfo Name]
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(TupIdentBase NoInfo Name)
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(LambdaBase NoInfo Name)
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(TupleLambdaBase NoInfo Name)
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(BasicValue -> Value)
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Int
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(BasicValue -> Value)
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(BasicValue -> Value)
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(BasicValue -> Value)
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(BasicValue -> Value)
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(BasicValue -> Value)
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Value
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(BasicValue -> Value)
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(BasicValue -> Value)
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[Value]
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[Value]
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In the second argument of `happySpecReduce_3', namely
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`happyReduction_191'
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In the expression: happySpecReduce_3 38# happyReduction_191
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In an equation for `happyReduce_191':
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happyReduce_191 = happySpecReduce_3 38# happyReduction_191
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**NOT NICE NOT NICE AT ALL**
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### MONADA CAN I HAZ
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MAYHAPS U NEED TO PARSE DIFFERENT THAN NORMAL KAY. HOW U THINK. YES:
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MENTALINCRMENTAL PARSING IT IS
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YOU GOT NEED TO PARSE IO GETLINE SOURCES YEAH
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PARSE EXPRESSION "2 + 1 \*4" OVER MULTI LINES LIKE THIS HERE
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WELCOM TO DA FUNKY MULTILINE EXPRESSION PARSER; ENTER UR EXPRESSION
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> 2 +
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1 *4
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TY GOT IT!! PARSED EXPRESSION IS "2 + 1 * 4" AND U NICE; RESULT IS 6 BTW
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>
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PARSER SHOULD KNOW "YEAH NOT DUHNE PARSIN YET" WHEN "2 +" READ, SHOULD
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TEHN READ NEW LINE AND PARSE MORE!
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WE CAN PARSE FROM BEGINNING EVERY TIME SURE BUT INEFECICIENT!!!
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BUT HOW WE SHOULD / COULD DO THAT SMARTLY I IMPLORE TO LIKE ASK U
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YES WE USE CONTINUATION WHICH SMART. LOOK ATTOPARSEC USE CONTINUATION IN
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RETURN!
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[<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)
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YEAH BUT NOT IN HAPPY............
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SO WE MAKE IT MANUAL. WE SPECIFY OWN LEXER AND IMPROVE MONAD. WHEN END
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OF LINE IS REACH, WE TELL PARSER (FROM INSIDE DA PRASER) DAT DERE IS NO
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MORE EVER; IF THAT FAILS WE CATCH ERROR (EITHER-LIKE MONAD) AND READ NEW
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LINE FOR REALS
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CLEVER SOLUTION OF US! BUT IN PARSE EXPRESION EXAMPLE ABOV WE USE IO TO
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GETLINE
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**WE NOT WANT IO IN ALL PARSING.... EVER EVER!!!!!!!!**
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HOWTO ABSTRACT IO AWAY? WE WANT TYPE OF EXPORTED FUNCTIONS FROM PARSER
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TO NOT USE **IO** *AT ALL*
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SO WE USE WHATEVER MONAD TO GETLINE RIGHT?
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``` {.haskell}
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class GetLiner m where -- KAY SO m IS MONAD RIGHT
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getSomeLine :: m String
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instance GetLiner IO where
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getSomeLine = getLine
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```
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WAIT I DONT GET IT
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``` {.haskell}
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CLASS GETLINER M WHERE -- KAY SO M IS MONAD RIGHT
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GETSOMELINE :: M STRING
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INSTANCE GETLINER IO WHERE
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GETSOMELINE = GETLINE
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```
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MUCH BETTR. COZ TEHN WE CAN USE
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BUT YIAH WE COULD USE TYPE CONSTRAINTS!
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``` {.haskell}
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LEXER :: GETLINER M => M SOMETHNIG
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LEXER = MEHMEHMEH
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WOO <- GETSOMELINE
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MEH MEH
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```
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SURE COULD WORK WE NEED JUST TELL HAPPY BOUT IT.
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%MONAD { GETLINER M => SOMETHINNG M }
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FAILS MISERBLY.................... :-( :( :(
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WE ARE LEFT 4 PONDER HOW TO SOLVE! HOWTO ABSTRAKT OUT IO! HOW!!
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SOOOO..... WE NEED KINDA CONTINUATIN COMPUTATON MONADY THINGY. I GOT
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FRIEND WHO COME WIT CODE, SAY IT GOOD CODE. I CHECK, HE RIGHT! IS HERE
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``` {.haskell}
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DATA READLINEMONAD A = VALUE A
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| GETLINE (STRING -> READLINEMONAD A)
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INSTANCE MONAD READLINEMONAD WHERE
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RETURN = VALUE
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VALUE X >>= F = F X
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GETLINE G >>= F = GETLINE $ \S -> G S >>= F
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```
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HA CLEVER!!! NOW WE NEED NO TYPE CONSTRAINTS BECAUSE NOW COMPUTATION IS
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MONAD ITSELF! HOW YOU ASK.
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READLINEMONAD HAS NO IO OR ANY ELSE BUILTIN; IT GETS LINE BY CREATE
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FUNCTION WHICH TAKES LINE TO CONTINUU EXECUTION. AGAIN AND AGAIN! LINE
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CAN COME FROM ANYTHIN.
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EXAMPLE FOR USING RESULT!
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``` {.haskell}
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GETLINESFROMIO :: READLINEMONAD A -> IO A
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GETLINESFROMIO (VALUE X) = RETURN X
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GETLINESFROMIO (GETLINE F) = DO
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S <- GETLINE
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GETLINESFROMIO $ F S
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```
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U SEE WAT GOIN ON DERE! IN OUR LEXER WE NAMELI USED
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``` {.haskell}
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GETLINE VALUE
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```
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TO GET LINE (BECAUSE FITS WITH CLEVER MONAD!)
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**NICE-O!**
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CODE IN QUSTION
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---------------
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LOOKIE HER FOR FULL DETAILS (ALTHOU WITH NO FULL CAPS):
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[<HTTPS://RARRW.GITHUB.COM/HIPERFIT/L0LANGUAGE/MASTER/SRC/LANGUAGE/L0/PARSER/PARSER.Y>](https://raw.github.com/HIPERFIT/L0Language/master/src/Language/L0/Parser/Parser.y)
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CONCLUSION
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----------
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THIS IS ENTRELY OBJECTIVE.
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THIS IS ENTIREY OBJECTIVE.
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THIS IS ENTIRLY OBJECTIVE.
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