Script-Fu
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Script-Fu is a scripting extension for the GIMP, a bitmap graphics editor. It used to be based on SIOD (Scheme in One Defun), but was switched to TinyScheme as of GIMP 2.4.
It is a horrible enviroment for scripters, as it is lacking in documentation and usually provides cryptic error messages that force the user to debug on a best guess-basis.
For instance, users will have to guess their way to proper parameters for most functions, as the documentation only ever mentions the data types of these parameters.