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> To use with-open effectively, we must macroexpand it in our heads whenever it appears in the code. I'd like to add that if you find yourself needing to menta

> To use with-open effectively, we must macroexpand it in our heads whenever it appears in the code. I'd like to add that if you find yourself needing to mentally expand a macro every time you use/read it, you have a poor abstraction. Consider going back to the drawing board and coming up with a good abstraction instead.

lispm 11y ago
Right. For a macro which only implements a 'simple' syntactic transformation, I would expect that I need to understand the semantics anyway. Additionally I need to understand the syntax it implements. What I don't want at all, is to macroexpand macro forms. If I need to macroexpand those, then I would do this for debugging, when there is something wrong during expansion or with the generated code. I would also do the expansion not in my head, but using a function called 'macroexpand'. For example as a reader, I don't want to macroexpand the following form in my head: (with-open-file (foo "bar.text") (read foo)) What I really want is to understand the syntax of WITH-OPEN-FILE and semantics of such a form. To what it transforms itself is the least important thing I (as a code reader) want to know when dealing with macro forms. * it's a WITH- type macro which sets up a scope. * a WITH- type macro usually expects a variable, something which helps creating an object that is bound to the variable and a bunch of options (foo-var "the-file-name.text" :direction :input) * it then expects a body, a sequence of forms, where the variable FOO-VAR is bound to a file That's the syntax. The semantics is that at runtime it opens a file as a stream and makes sure that on all forms of exit, the stream gets closed. To what form this actually expands (even if it is a simple transformation) is uninteresting and may be different from implementation to implementation.

lispm 11y ago

Right. For a macro which only implements a 'simple' syntactic transformation, I would expect that I need to understand the semantics anyway. Additionally I need to understand the syntax it implements. What I don't want at all, is to macroexpand macro forms. If I need to macroexpand those, then I would do this for debugging, when there is something wrong during expansion or with the generated code. I would also do the expansion not in my head, but using a function called 'macroexpand'. For example as a reader, I don't want to macroexpand the following form in my head: (with-open-file (foo "bar.text") (read foo)) What I really want is to understand the syntax of WITH-OPEN-FILE and semantics of such a form. To what it transforms itself is the least important thing I (as a code reader) want to know when dealing with macro forms. * it's a WITH- type macro which sets up a scope. * a WITH- type macro usually expects a variable, something which helps creating an object that is bound to the variable and a bunch of options (foo-var "the-file-name.text" :direction :input) * it then expects a body, a sequence of forms, where the variable FOO-VAR is bound to a file That's the syntax. The semantics is that at runtime it opens a file as a stream and makes sure that on all forms of exit, the stream gets closed. To what form this actually expands (even if it is a simple transformation) is uninteresting and may be different from implementation to implementation.