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!Groovy

Official Site [https://groovy-lang.org]

!Eclipse

https://groovy-lang.org/ides.html > https://github.com/groovy/groovy-eclipse
    > https://github.com/groovy/groovy-eclipse/wiki
    > Install URL for Eclipse 4.19 (2021-03) = https://dist.springsource.org/release/GRECLIPSE/e4.19
    > choose 
                                Main Package > Eclipse Groovy Development Tools 4.1.0.v202103311613...
                  Note: "Maven Support" will cause Eclipse start failure
                > Restart > New Project ...

https://groovy.apache.org/download.html > latest stable (3.0.7) > binary

Explorer > PC > right click > properties > Advanced system settings > Environment Variables
                > New > "GROOVY_HOME" = C:\lang\groovy\groovy-3.0.7
                > Mark Path > Edit > New > "%GROOVY_HOME%\bin"

Note: add GROOVY_HOME and edit path both at user or system level !
Check 
                cmd > groovy -v
Console:
- stop printing all variables with a final "return"

Turn off warnings:
--add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.lang.invoke=ALL-UNNAMED