{"id":961,"date":"2013-12-21T09:58:53","date_gmt":"2013-12-21T09:58:53","guid":{"rendered":"http:\/\/putridparrot.com\/blog\/?p=961"},"modified":"2013-12-21T10:36:41","modified_gmt":"2013-12-21T10:36:41","slug":"modules-in-f","status":"publish","type":"post","link":"https:\/\/putridparrot.com\/blog\/modules-in-f\/","title":{"rendered":"Modules in F#"},"content":{"rendered":"

Modules allow us to break up source code into multiple files. There are two types of module, a top-level<\/strong> module and local<\/strong> modules.<\/p>\n

Note: I’ve omitted any namespaces, but for completeness of this post, a name space would be added as the first line in the module files (if required) as per<\/p>\n

\r\nnamespace MyNamespace\r\n\r\nmodule MyModule =\r\n   let square x = x * x\r\n<\/pre>\n
<\/em><\/p>\n
The top-level module<\/strong><\/p>\n
The top-level module is basically a module which contains all the code for an application and it has slightly different rules regarding it’s layout compared to the local modules (see Modules (F#)<\/a>.<\/p>\n
Reproducing a little from the above link we see that a top-level module does not need an = sign at the end of the module name and declarations need not be indented, for example the following is perfectly acceptable in a top-level module but not a local module<\/p>\n
\r\nmodule MyModule\r\n\r\nlet hello = \r\n   printfn "Hello"\r\n<\/pre>\n
Local Modules<\/strong><\/p>\n
Local modules are basically re-usable files. The usual usage would be to group together related code. Unlike the top-level module, local modules require indented formatting as well as an = after the module name, so the previously define code for a top-level module would look like the following code in a local module<\/p>\n
\r\nmodule MyModule =\r\n\r\n   let hello =\r\n      printfn "Hello"\r\n<\/pre>\n
The Program\/EntryPoint module<\/strong><\/p>\n
By default the code generated by Visual Studio as the starting point for an F# applications looks like<\/p>\n
\r\n[<EntryPoint>]\r\nlet main argv = \r\n    printfn "%A" argv\r\n    0 \/\/ return an integer exit code\r\n<\/pre>\n
But implicitly this will be compiled as<\/p>\n
\r\nmodule Program\r\n[<EntryPoint>]\r\nlet main argv = \r\n    printfn "%A" argv\r\n    0 \/\/ return an integer exit code\r\n<\/pre>\n
Thus conversely the module name of a top-level module can be omitted if it’s the only file in the application.<\/p>\n
Inner Modules<\/strong><\/p>\n
Not only can a file be declared as a module but you can also have modules nested within modules, for example<\/p>\n
\r\nmodule GrandParent =\r\n   module Parent =\r\n      module Child =\r\n         let x = 100\r\n<\/pre>\n
Within a top-level module we can define this as <\/p>\n
\r\nmodule GrandParent\r\n\r\nmodule Parent =\r\n   module Child =\r\n      let x = 100\r\n<\/pre>\n
in other words the top level module does not need the = sign or the indenting of the Parent module.<\/p>\n
How to use a module<\/strong><\/p>\n
So we’ve shown how to declare modules but at some point we need to use them, to achieve this we use the following<\/p>\n
\r\nopen MyModule\r\n<\/pre>\n
If we’d had a namespace we could open the namespace such as open MyNamespace<\/em>. In such a case where modules were in the namespace we could prefix them on the functions, such as MyModule.square 3<\/em>. Alternatively we could open the namespace and specific module(s) such as open MyNamespace.MyModule<\/em> and thus have no need to prefix the functions with the module name.<\/p>\n","protected":false},"excerpt":{"rendered":"
Modules allow us to break up source code into multiple files. There are two types of module, a top-level module and local modules. Note: I’ve omitted any namespaces, but for completeness of this post, a name space would be added as the first line in the module files (if required) as per namespace MyNamespace module […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[6],"tags":[],"class_list":["post-961","post","type-post","status-publish","format-standard","hentry","category-f"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/961","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/comments?post=961"}],"version-history":[{"count":8,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/961\/revisions"}],"predecessor-version":[{"id":969,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/961\/revisions\/969"}],"wp:attachment":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/media?parent=961"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/categories?post=961"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/tags?post=961"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}