A programming language supports first class functions, when function references can be assigned as arguments and returned as values from other functions. <\/p>\n\n\n\n
In a language such as Genero BDL that doesn’t natively support the definition of classes, first class functions are helpful for code injections and callback functionality. <\/p>\n\n\n\n
For instance, if a module performs a lengthy task, a callback can provide feedback to the calling module displaying progress to the user. This can be done with function references.<\/p>\n\n\n\n
Starting with version 3.10 of Genero BDL, first class functions were added to the language through the addition of a function type definition and function type parameters.<\/p>\n\n\n\n
For example if I can can declare a function reference type that can then be used in variable, and parameter definition. <\/p>\n\n\n\n
\nTYPE callback_function_type FUNCTION(percent int, message string) returns int\n<\/code><\/pre>\n\n\n\nFUNCTION do_work(progress_callback callback_function_type)\ndefine\n rsp int \n...\n...\ncall progress_callback(25,\"Making progress\")\n returning rsp\n...\nend function<\/code><\/pre>\n\n\n\nUsing types is my preferred way to define first class function types but the FUNCTION(…) syntax can be used to define first class functions as local, module and function arguments. <\/p>\n\n\n\n
DEFINE callback FUNCTION(percent int, message string) returns int<\/code><\/pre>\n\n\n\nSimilar syntax can be used to define a function argument to another function<\/p>\n\n\n\n
FUNCTION do_work(progress_callback FUNCTION(percent INT, message INT) returns int)<\/code><\/pre>\n\n\n\nI find that syntax can be awkward so I prefer to use types to declare first class function parameters as shown in the first two examples.<\/p>\n\n\n\n
FUNCTION display_progress(percent int, message string) returns int\n...\nend function<\/code><\/pre>\n\n\n\nFor myself, first class functions are useful for callback and injecting additional functionality into modules. <\/p>\n\n\n\n