In page 19 of Pratical Clojure by Luke VanderHart & Stuart Sierra, Chapter 2, there is a paragraph,
Special forms definition : Special forms are a particular type of composite form. For most purposes, they are used very similarly to a function call. The difference is that the first form of a special form is not a function defined somewhere, but a special system form that’s built into Clojure. 1st question, Is the form word is a typo here? Isn't the word will be item? If not, is def a form? That means, this code contains 3 forms. :-s Cause later on, when the write was explaining an example, he used item. (def message "Hello, World!") Analyzing the first form, (def message "Hello, World!") , you see first that it is enclosed in parenthesis. Therefore, it is a list, and will be evaluated as a function application or a special form. There are three items in the list: def, message and "Hello, World!". The first item on the list, def, will be the function or special form that is called. In this case, it's a special form. But like a function, it takes two parameters—the var to define, and the value to which to bind it. Evaluating this form creates a var which establishes a binding of the value "Hello, World!" to the symbol message. 2nd question, Is a composite form is a special form only when, the first item of a list is something that is only predefined withing Clojure? If yes, then is it possible to create custom special form? Is then the custom composite form is gonna be called as a special form? Cause, according to the definition, my custom is not something built in clojure, it is defined somewhere else? EDIT: I guess the answer to my first question is no, its not a typo. def IS a form. cause later on the write said, The second form (println message) is also a list and this time it’s a normal function application. It has two component forms—each of them is a symbol That means, (println message) > the whole thing is a form, and every thing else(function arguments) that it holds is also a form. But, at the beginning the writer said, there are four basic varieties of forms. 1. Literal, 2. Symbol, 3. Composite form and 4. Special form. According to the definition of Symbols from the book, its not a symbol. Symbol Definition: Symbols are forms which resolve to a value. They may be thought of as roughly similar to variables, although this is not technically accurate since they are not actually variable in the same way variables in most languages are. In Clojure, symbols are used to identify function arguments, and globally or locally defined values. Symbols and their resolution are discussed in more detail in the following sections. Cause, writing def and pressing return key produces the following error message, In which category, def falls into? -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
