Info Catalog calc: Declarations calc: Declarations calc: Kinds of Declarations

calc: Declaration Basics

 
 7.6.1 Declaration Basics
 ------------------------
 
 The ‘s d’ (‘calc-declare-variable’) command is the easiest way to make a
 declaration for a variable.  This command prompts for the variable name,
 then prompts for the declaration.  The default at the declaration prompt
 is the previous declaration, if any.  You can edit this declaration, or
 press ‘C-k’ to erase it and type a new declaration.  (Or, erase it and
 press <RET> to clear the declaration, effectively “undeclaring” the
 variable.)
 
    A declaration is in general a vector of “type symbols” and “range”
 values.  If there is only one type symbol or range value, you can write
 it directly rather than enclosing it in a vector.  For example, ‘s d foo
 <RET> real <RET>’ declares ‘foo’ to be a real number, and ‘s d bar <RET>
 [int, const, [1..6]] <RET>’ declares ‘bar’ to be a constant integer
 between 1 and 6.  (Actually, you can omit the outermost brackets and
 Calc will provide them for you: ‘s d bar <RET> int, const, [1..6]
 <RET>’.)
 
    Declarations in Calc are kept in a special variable called ‘Decls’.
 This variable encodes the set of all outstanding declarations in the
 form of a matrix.  Each row has two elements: A variable or vector of
 variables declared by that row, and the declaration specifier as
 described above.  You can use the ‘s D’ command to edit this variable if
 you wish to see all the declarations at once.  Operations on
 Variables, for a description of this command and the ‘s p’ command
 that allows you to save your declarations permanently if you wish.
 
    Items being declared can also be function calls.  The arguments in
 the call are ignored; the effect is to say that this function returns
 values of the declared type for any valid arguments.  The ‘s d’ command
 declares only variables, so if you wish to make a function declaration
 you will have to edit the ‘Decls’ matrix yourself.
 
    For example, the declaration matrix
 
      [ [ foo,       real       ]
        [ [j, k, n], int        ]
        [ f(1,2,3),  [0 .. inf) ] ]
 
 declares that ‘foo’ represents a real number, ‘j’, ‘k’ and ‘n’ represent
 integers, and the function ‘f’ always returns a real number in the
 interval shown.
 
    If there is a declaration for the variable ‘All’, then that
 declaration applies to all variables that are not otherwise declared.
 It does not apply to function names.  For example, using the row ‘[All,
 real]’ says that all your variables are real unless they are explicitly
 declared without ‘real’ in some other row.  The ‘s d’ command declares
 ‘All’ if you give a blank response to the variable-name prompt.
 

Info Catalog calc: Declarations calc: Declarations calc: Kinds of Declarations