Try Monad in Java

master
bvn13 3 years ago
parent 1a8068d6ba
commit 8b651812de
  1. 16
      build.gradle
  2. 172
      gradlew
  3. 84
      gradlew.bat
  4. 2
      settings.gradle
  5. 61
      src/main/java/com/bvn13/jmonad/Failure.java
  6. 67
      src/main/java/com/bvn13/jmonad/Success.java
  7. 49
      src/main/java/com/bvn13/jmonad/Try.java
  8. 26
      src/main/java/com/bvn13/jmonad/exceptions/ValueNotFoundException.java
  9. 92
      src/test/java/com/bvn13/jmonad/TryTest.java

@ -0,0 +1,16 @@
plugins {
id 'java'
}
group 'com.bvn13'
version '1.0-SNAPSHOT'
sourceCompatibility = 1.8
repositories {
mavenCentral()
}
dependencies {
testCompile group: 'junit', name: 'junit', version: '4.12'
}

172
gradlew vendored

@ -0,0 +1,172 @@
#!/usr/bin/env sh
##############################################################################
##
## Gradle start up script for UN*X
##
##############################################################################
# Attempt to set APP_HOME
# Resolve links: $0 may be a link
PRG="$0"
# Need this for relative symlinks.
while [ -h "$PRG" ] ; do
ls=`ls -ld "$PRG"`
link=`expr "$ls" : '.*-> \(.*\)$'`
if expr "$link" : '/.*' > /dev/null; then
PRG="$link"
else
PRG=`dirname "$PRG"`"/$link"
fi
done
SAVED="`pwd`"
cd "`dirname \"$PRG\"`/" >/dev/null
APP_HOME="`pwd -P`"
cd "$SAVED" >/dev/null
APP_NAME="Gradle"
APP_BASE_NAME=`basename "$0"`
# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
DEFAULT_JVM_OPTS=""
# Use the maximum available, or set MAX_FD != -1 to use that value.
MAX_FD="maximum"
warn () {
echo "$*"
}
die () {
echo
echo "$*"
echo
exit 1
}
# OS specific support (must be 'true' or 'false').
cygwin=false
msys=false
darwin=false
nonstop=false
case "`uname`" in
CYGWIN* )
cygwin=true
;;
Darwin* )
darwin=true
;;
MINGW* )
msys=true
;;
NONSTOP* )
nonstop=true
;;
esac
CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
# Determine the Java command to use to start the JVM.
if [ -n "$JAVA_HOME" ] ; then
if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
# IBM's JDK on AIX uses strange locations for the executables
JAVACMD="$JAVA_HOME/jre/sh/java"
else
JAVACMD="$JAVA_HOME/bin/java"
fi
if [ ! -x "$JAVACMD" ] ; then
die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
Please set the JAVA_HOME variable in your environment to match the
location of your Java installation."
fi
else
JAVACMD="java"
which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
Please set the JAVA_HOME variable in your environment to match the
location of your Java installation."
fi
# Increase the maximum file descriptors if we can.
if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
MAX_FD_LIMIT=`ulimit -H -n`
if [ $? -eq 0 ] ; then
if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
MAX_FD="$MAX_FD_LIMIT"
fi
ulimit -n $MAX_FD
if [ $? -ne 0 ] ; then
warn "Could not set maximum file descriptor limit: $MAX_FD"
fi
else
warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
fi
fi
# For Darwin, add options to specify how the application appears in the dock
if $darwin; then
GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
fi
# For Cygwin, switch paths to Windows format before running java
if $cygwin ; then
APP_HOME=`cygpath --path --mixed "$APP_HOME"`
CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
JAVACMD=`cygpath --unix "$JAVACMD"`
# We build the pattern for arguments to be converted via cygpath
ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
SEP=""
for dir in $ROOTDIRSRAW ; do
ROOTDIRS="$ROOTDIRS$SEP$dir"
SEP="|"
done
OURCYGPATTERN="(^($ROOTDIRS))"
# Add a user-defined pattern to the cygpath arguments
if [ "$GRADLE_CYGPATTERN" != "" ] ; then
OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
fi
# Now convert the arguments - kludge to limit ourselves to /bin/sh
i=0
for arg in "$@" ; do
CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
CHECK2=`echo "$arg"|egrep -c "^-"` ### Determine if an option
if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then ### Added a condition
eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
else
eval `echo args$i`="\"$arg\""
fi
i=$((i+1))
done
case $i in
(0) set -- ;;
(1) set -- "$args0" ;;
(2) set -- "$args0" "$args1" ;;
(3) set -- "$args0" "$args1" "$args2" ;;
(4) set -- "$args0" "$args1" "$args2" "$args3" ;;
(5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
(6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
(7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
(8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
(9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
esac
fi
# Escape application args
save () {
for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
echo " "
}
APP_ARGS=$(save "$@")
# Collect all arguments for the java command, following the shell quoting and substitution rules
eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
cd "$(dirname "$0")"
fi
exec "$JAVACMD" "$@"

84
gradlew.bat vendored

@ -0,0 +1,84 @@
@if "%DEBUG%" == "" @echo off
@rem ##########################################################################
@rem
@rem Gradle startup script for Windows
@rem
@rem ##########################################################################
@rem Set local scope for the variables with windows NT shell
if "%OS%"=="Windows_NT" setlocal
set DIRNAME=%~dp0
if "%DIRNAME%" == "" set DIRNAME=.
set APP_BASE_NAME=%~n0
set APP_HOME=%DIRNAME%
@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
set DEFAULT_JVM_OPTS=
@rem Find java.exe
if defined JAVA_HOME goto findJavaFromJavaHome
set JAVA_EXE=java.exe
%JAVA_EXE% -version >NUL 2>&1
if "%ERRORLEVEL%" == "0" goto init
echo.
echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
echo.
echo Please set the JAVA_HOME variable in your environment to match the
echo location of your Java installation.
goto fail
:findJavaFromJavaHome
set JAVA_HOME=%JAVA_HOME:"=%
set JAVA_EXE=%JAVA_HOME%/bin/java.exe
if exist "%JAVA_EXE%" goto init
echo.
echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
echo.
echo Please set the JAVA_HOME variable in your environment to match the
echo location of your Java installation.
goto fail
:init
@rem Get command-line arguments, handling Windows variants
if not "%OS%" == "Windows_NT" goto win9xME_args
:win9xME_args
@rem Slurp the command line arguments.
set CMD_LINE_ARGS=
set _SKIP=2
:win9xME_args_slurp
if "x%~1" == "x" goto execute
set CMD_LINE_ARGS=%*
:execute
@rem Setup the command line
set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
@rem Execute Gradle
"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
:end
@rem End local scope for the variables with windows NT shell
if "%ERRORLEVEL%"=="0" goto mainEnd
:fail
rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
rem the _cmd.exe /c_ return code!
if not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
exit /b 1
:mainEnd
if "%OS%"=="Windows_NT" endlocal
:omega

@ -0,0 +1,2 @@
rootProject.name = 'jmonad'

@ -0,0 +1,61 @@
package com.bvn13.jmonad;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Function;
/**
* Created by bvn13 on 10.06.2019.
*/
public class Failure<T> extends Try<T> {
private final Throwable e;
Failure(Throwable e) {
this.e = e;
}
@Override
public T get() throws Throwable {
throw e;
}
@Override
public T orElse(T value) {
return value;
}
@Override
public <U> Try<U> flatMap(Function<? super T, ? extends U> f) {
Objects.requireNonNull(f);
return Try.failure(e);
}
@Override
public Try<T> filter(Function<? super T, ? extends Boolean> f) {
Objects.requireNonNull(f);
return Try.failure(e);
}
@Override
public Try<T> map(Function<? super T, ? extends T> f) {
Objects.requireNonNull(f);
return Try.failure(e);
}
@Override
public T orElseThrow(Throwable e) throws Throwable {
Objects.requireNonNull(e);
throw e;
}
@Override
public Optional<T> toOptional() {
return Optional.empty();
}
@Override
public boolean isSuccess() {
return false;
}
}

@ -0,0 +1,67 @@
package com.bvn13.jmonad;
import com.bvn13.jmonad.exceptions.ValueNotFoundException;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Function;
/**
* Created by bvn13 on 10.06.2019.
*/
public class Success<T> extends Try<T> {
private final T value;
Success(T value) {
this.value = value;
}
@Override
public T get() {
return value;
}
@Override
public T orElse(T value) {
return this.value;
}
@Override
public <U> Try<U> flatMap(Function<? super T, ? extends U> f) {
Objects.requireNonNull(f);
return Try.successful(f.apply(value));
}
@Override
public Try<T> filter(Function<? super T, ? extends Boolean> f) {
Objects.requireNonNull(f);
if (f.apply(value)) {
return Try.successful(value);
} else {
return Try.failure(new ValueNotFoundException("not found"));
}
}
@Override
public Try<T> map(Function<? super T, ? extends T> f) {
Objects.requireNonNull(f);
return Try.successful(f.apply(value));
}
@Override
public T orElseThrow(Throwable e) throws Throwable {
Objects.requireNonNull(e);
return value;
}
@Override
public Optional<T> toOptional() {
return Optional.ofNullable(value);
}
@Override
public boolean isSuccess() {
return true;
}
}

@ -0,0 +1,49 @@
package com.bvn13.jmonad;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Function;
import java.util.function.Supplier;
/**
* Full implementation of Try monad
* @see <a href="https://medium.com/swlh/write-a-monad-in-java-seriously-50a9047c9839">Source article</a>
*
* Created by bvn13 on 10.06.2019.
*/
public abstract class Try<T> {
public static <U> Try<U> ofThrowable(Supplier<U> f) {
Objects.requireNonNull(f);
try {
return Try.successful(f.get());
} catch (Throwable e) {
return Try.failure(e);
}
}
public static <U> Success<U> successful(U u) {
return new Success<>(u);
}
public static <U> Failure<U> failure(Throwable e) {
return new Failure<>(e);
}
public abstract T get() throws Throwable;
public abstract T orElse(T value);
public abstract <U> Try<U> flatMap(Function<? super T, ? extends U> f);
public abstract Try<T> filter(Function<? super T, ? extends Boolean> f);
public abstract Try<T> map(Function<? super T, ? extends T> f);
public abstract T orElseThrow(Throwable e) throws Throwable;
public abstract Optional<T> toOptional();
public abstract boolean isSuccess();
}

@ -0,0 +1,26 @@
package com.bvn13.jmonad.exceptions;
/**
* Created by bvn13 on 10.06.2019.
*/
public class ValueNotFoundException extends RuntimeException {
public ValueNotFoundException() {
super();
}
public ValueNotFoundException(String message) {
super(message);
}
public ValueNotFoundException(String message, Throwable cause) {
super(message, cause);
}
public ValueNotFoundException(Throwable cause) {
super(cause);
}
protected ValueNotFoundException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
super(message, cause, enableSuppression, writableStackTrace);
}
}

@ -0,0 +1,92 @@
package com.bvn13.jmonad;
import org.junit.Test;
import static org.junit.Assert.*;
/**
* Created by bvn13 on 10.06.2019.
*/
public class TryTest {
@Test
public void testTryFirstProbe() throws Throwable {
Try.ofThrowable(() -> String.valueOf(10))
.get();
}
@Test
public void testTryInteger() throws Throwable {
Try<Integer> value = Try.ofThrowable(() -> Integer.valueOf("1"));
assertEquals(Integer.valueOf(1), value.get());
}
@Test
public void testTryIntegerAdd() throws Throwable {
String value = Try.ofThrowable(() -> Integer.valueOf("1"))
.flatMap(v -> String.format("%d", v))
.get();
assertEquals("1", value);
}
@Test
public void testFailureWithDefault() {
int value = Try.ofThrowable(() -> Integer.valueOf("T"))
.orElse(5);
assertEquals(5, value);
}
@Test
public void testFilter() throws Throwable {
int value = Try.ofThrowable(() -> Integer.valueOf("1"))
.filter(i -> i > 0)
.get();
assertEquals(1, value);
int notValue = Try.ofThrowable(() -> Integer.valueOf("1"))
.filter(i -> i < 0)
.orElse(10);
assertEquals(10, notValue);
}
@Test
public void testMap() throws Throwable {
int value = Try.ofThrowable(() -> Integer.valueOf("1"))
.map(i -> i + 20)
.get();
assertEquals(21, value);
}
@Test
public void testOrElseThrow() throws Throwable {
Throwable t = null;
try {
int value = Try.ofThrowable(() -> Integer.valueOf("1"))
.filter(v -> v < 0)
.orElseThrow(new IllegalArgumentException("!!!"));
} catch (Throwable e) {
t = e;
}
assertTrue(t instanceof IllegalArgumentException);
}
@Test
public void testToOptional() {
int value = Try.ofThrowable(() -> Integer.valueOf("1"))
.toOptional().orElse(2);
assertEquals(1, value);
int notValue = Try.ofThrowable(() -> Integer.valueOf(""))
.toOptional().orElse(2);
assertEquals(2, notValue);
}
@Test
public void testIsSuccess() {
boolean success = Try.ofThrowable(() -> Integer.valueOf("1")).isSuccess();
assertTrue(success);
boolean failure = Try.ofThrowable(() -> Integer.valueOf("")).isSuccess();
assertFalse(failure);
}
}
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