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Questions tagged [happy]

Happy is a YACC-like parse generator for Haskell

Happy is a like parse generator for the programming language.

106 questions
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What is the advantage of using a parser generator like happy as opposed to using parser combinators?

To learn how to write and parse a context-free grammar I want to choose a tool. For Haskell, there are two big options: Happy, which generates a parser from a grammar description and *Parsec, which allows you to directly code a parser in…
fuz
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Managing position information with Alex and Happy

I'm learning to use Alex and Happy to write a small compiler. I want to maintain line and column information for my AST nodes so that I can provide meaningful error messages to the user. To illustrate how I plan to do it, I wrote a small example…
gnuvince
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1 answer

cabal-install does not retain the version for happy

I've trying to do cabal install hoogle but there is a hickup with the haskell-src-exts-1.13.5 dependency: Configuring haskell-src-exts-1.13.5... setup: The program happy version >=1.17 is required but it could not be found. When I try to do cabal…
Alexander Kondratskiy
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How can I make Stack call Happy, Alex and other build tools?

As part of my compiler, I need alex and happy to run as part of my build process. How does Stack support this scenario? Bonus: how can I register alex and happy as compile-time dependencies?
Carl Patenaude Poulin
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1 answer

Parsec or happy (with alex) or uu-parsinglib

I am going to write a parser of verilog (or vhdl) language and will do a lot of manipulations (sort of transformations) of the parsed data. I intend to parse really big files (full Verilog designs, as big as 10K lines) and I will ultimately support…
Dilawar
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Using alex/happy with Cabal

I'm writing a compiler for a class I'm taking. The class isn't specifically Haskell but I'm using Haskell to write my compiler and interpreter. I have a cabal package setup to hopefully make it easy for my prof to run/compile. I have happy and alex…
Edward
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Are there any tutorials on building a simple interpreter using Alex + Happy?

I'm working on a school project where I have to build an interpreter for a simple language using Alex + Happy in Haskell. After looking through the documentation I understand most of it, but would like to see a full blown example on using the tools.
Carlos G.
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How to use an Alex monadic lexer with Happy?

I'm trying to learn using Alex + Happy to build parser, in particular I'm interested in learning to use the monad wrapper of Alex. I have already looked at the documentation of Alex and Happy but I they are both, for me, really lacking any useful…
Bakuriu
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Overriding "Internal Happy Error" - notHappyAtAll

I am using Happy to generate a parser. I have found that when I give it tokens which match part of the grammar at a lower level than the top level (such as giving it an expression on it's own, that isn't part of a statement), I get an "Internal…
Jack
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How do Happy and Alex bootstrap themselves into being?

The source tree for happy contains AttrGrammarParser.ly and Parser.ly and the source tree for alex contains Scan.x. Yet, as far as I can tell in order to compile happy, we need to transform the .ly files into .lhs files using... happy, and in order…
rampion
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Happy: Order of Productions Removes R/R Conflicts

I have a grammar that, depending on the order of productions, happy reports 3 reduce/reduce conflicts or none. The minimal example I can find is: %tokentype {Token} %token int { Int } '-' { Neg } both { Both } %nonassoc…
sfogarty
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Suppress certain Haskell Alex/Happy compilation messages

When creating either a Lexer.x or a Parser.y parser using the Alex lexer generator or the Happy parser generator, compiling those into Haskell files, and compiling those into object files, by default this will generate the following "warnings": $…
Simon Shine
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JS: regex for numbers and spaces?

I'm using happyJS and use the regex underneath for phone validation phone: function (val) { return /^(?:[0-9]+$)/.test(val); } However this ONLY allows numbers. I want the user to be able to enter spaces as well like 238 238 45383 Any…
matt
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Happy Context-Dependent Operator Precedence

I have two snippets of Happy code here, one that uses normal precedence rules, and one that uses context-dependent precedence rules (both of which are described here). Normal: %left '+' %left '*' %% Exp :: { Exp } : Exp '+' Exp { Plus $1 $3 } …
Kyle McCormick
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What's the %% for in Happy?

I'm building a parser with Happy and noticed this is the online documentation: Like yacc, we include %% here, for no real reason. %% There must be a reason though, even if it's trivial. Does anyone know what it is?
Nick Brunt
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