Add remaining haskell book exercises

Haskell-book/24/LearnParsers/.gitignore

@@ -0,0 +1,3 @@
+.stack-work/
+LearnParsers.cabal
+*~

Haskell-book/24/LearnParsers/ChangeLog.md

@@ -0,0 +1,3 @@
+# Changelog for LearnParsers
+
+## Unreleased changes

Haskell-book/24/LearnParsers/Setup.hs

@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain

Haskell-book/24/LearnParsers/app/Main.hs

@@ -0,0 +1,24 @@
+module Main where
+
+import Control.Applicative
+import LearnParsers
+import Text.Fractions
+import Text.Trifecta
+import Text.Parser.Combinators
+
+unitOfSuccess :: (TokenParsing m, Monad m) => m Integer
+unitOfSuccess = do
+    number <- integer
+    _ <- eof
+    return number
+
+type FractionOrNumber = Either Rational Integer
+
+parseFractionOrNumber :: Parser FractionOrNumber
+parseFractionOrNumber =  skipMany (oneOf "\n")
+     >> (Left <$> try virtuousFraction)
+    <|> (Right <$> integer)
+
+main :: IO ()
+main = do
+    print $ parseString unitOfSuccess mempty "123"

Haskell-book/24/LearnParsers/package.yaml

@@ -0,0 +1,24 @@
+name:                LearnParsers
+version:             0.1.0.0
+author:              "Eugen Wissner"
+maintainer:          "belka@caraus.de"
+copyright:           "2018 Eugen Wissner"
+
+dependencies:
+- base >= 4.7 && < 5
+- trifecta
+- parsers
+
+library:
+  source-dirs: src
+
+executables:
+  LearnParsers:
+    main:                Main.hs
+    source-dirs:         app
+    ghc-options:
+    - -threaded
+    - -rtsopts
+    - -with-rtsopts=-N
+    dependencies:
+    - LearnParsers

Haskell-book/24/LearnParsers/src/LearnParsers.hs

@@ -0,0 +1,45 @@
+module LearnParsers where
+
+import Text.Trifecta
+
+stop :: Parser a
+stop = unexpected "stop"
+
+-- read a single character '1'
+one = char '1'
+
+-- read a single character '1', then die
+one' = one >> stop
+-- equivalent to char '1' >> stop
+
+-- read two characters, '1', and '2'
+oneTwo = char '1' >> char '2'
+
+-- read two characters,
+-- '1' and '2', then die
+
+oneTwo' = oneTwo >> stop
+
+testParse :: Parser Char -> IO ()
+testParse p = print $ parseString p mempty "123"
+
+pNL s = putStrLn ('\n' : s)
+
+oneTwoThree :: Parser String
+oneTwoThree = choice
+            [ string "123"
+            , string "12"
+            , string "1"
+            ]
+
+oneTwoThree' = oneTwoThree >> stop
+
+testParse' :: Parser String -> IO ()
+testParse' p = print $ parseString p mempty "123"
+
+oneTwoThree'' :: Parser Char
+oneTwoThree'' = choice
+        [ one
+        , oneTwo
+        , char '1' >> char '2' >> char '3'
+        ]

Haskell-book/24/LearnParsers/src/Text/Fractions.hs

@@ -0,0 +1,31 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Text.Fractions where
+
+import Control.Applicative
+import Data.Ratio ((%))
+import Text.Trifecta
+
+badFraction = "1/0"
+
+alsoBad = "10"
+
+shouldWork = "1/2"
+
+shouldAlsoWork = "2/1"
+
+parseFraction :: Parser Rational
+parseFraction = do
+    numerator <- decimal
+    char '/'
+    denominator <- decimal
+    return (numerator % denominator)
+
+virtuousFraction :: Parser Rational
+virtuousFraction = do
+    numerator <- decimal
+    char '/'
+    denominator <- decimal
+    case denominator of
+      0 -> fail "Denominator cannot be zero"
+      _ -> return $ numerator % denominator

Haskell-book/24/LearnParsers/stack.yaml

@@ -0,0 +1,66 @@
+# This file was automatically generated by 'stack init'
+#
+# Some commonly used options have been documented as comments in this file.
+# For advanced use and comprehensive documentation of the format, please see:
+# https://docs.haskellstack.org/en/stable/yaml_configuration/
+
+# Resolver to choose a 'specific' stackage snapshot or a compiler version.
+# A snapshot resolver dictates the compiler version and the set of packages
+# to be used for project dependencies. For example:
+#
+# resolver: lts-3.5
+# resolver: nightly-2015-09-21
+# resolver: ghc-7.10.2
+# resolver: ghcjs-0.1.0_ghc-7.10.2
+# resolver:
+#  name: custom-snapshot
+#  location: "./custom-snapshot.yaml"
+resolver: lts-11.0
+
+# User packages to be built.
+# Various formats can be used as shown in the example below.
+#
+# packages:
+# - some-directory
+# - https://example.com/foo/bar/baz-0.0.2.tar.gz
+# - location:
+#    git: https://github.com/commercialhaskell/stack.git
+#    commit: e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+# - location: https://github.com/commercialhaskell/stack/commit/e7b331f14bcffb8367cd58fbfc8b40ec7642100a
+#   extra-dep: true
+#  subdirs:
+#  - auto-update
+#  - wai
+#
+# A package marked 'extra-dep: true' will only be built if demanded by a
+# non-dependency (i.e. a user package), and its test suites and benchmarks
+# will not be run. This is useful for tweaking upstream packages.
+packages:
+- .
+# Dependency packages to be pulled from upstream that are not in the resolver
+# (e.g., acme-missiles-0.3)
+# extra-deps: []
+
+# Override default flag values for local packages and extra-deps
+# flags: {}
+
+# Extra package databases containing global packages
+# extra-package-dbs: []
+
+# Control whether we use the GHC we find on the path
+# system-ghc: true
+#
+# Require a specific version of stack, using version ranges
+# require-stack-version: -any # Default
+# require-stack-version: ">=1.6"
+#
+# Override the architecture used by stack, especially useful on Windows
+# arch: i386
+# arch: x86_64
+#
+# Extra directories used by stack for building
+# extra-include-dirs: [/path/to/dir]
+# extra-lib-dirs: [/path/to/dir]
+#
+# Allow a newer minor version of GHC than the snapshot specifies
+# compiler-check: newer-minor