6.6.0. Symbolic Constants

(lsh/libc/constants.lsh)

header files of C libraries are often filled with large amounts of #define directives that define numerical macros, flags and other constants. Interfacing these libraries to Lush requires to turn those constants into Lisp symbols. Lush contains a mechanism for defining such constants without filling up the global variable name space and risquing name clashes. Constants can be defined with the (defconstant "constant-name" value) directive. Constants can later be accessed using the @constant-name macro or the @@constant-name macro. The @ macro expands into a macro that evaluates to the value, while @@ directly expands to the value at read time.
See: @ identifier
See: (defconstant identifier val )

6.6.0.0. (defconstant identifier val)

(lsh/libc/constants.lsh)

Defines a symbolic constant named identifier and equal to val . Argument identifier must be a string or a symbol. Argument val must be a number or a string. These constant values are not accessible as variables but are accessible using the |@| macro-character.

6.6.0.1. @identifier @@identifier

(lsh/libc/constants.lsh)

These macro-character expand to a expressions that retrieve the value of the symbolic constant named identifier . The @ form causes the retrieval to occur at macro-expansion time. while the @@ form causes the retrieval to occur at read time. These macros are particularly useful for using symbolic constants in compiled code.

Argument identifier must be a legal C identifier name.

Compatibility notes:

If identifier has not been defined using defconstant , the global value of the symbol named identifier is used.
If the macro-character |@| cannot read a legal C identifier name, it reads a lisp expression and arranges for that expression to be evaluated during the macro expansion time.
The expansion of the @@ form depends on the execution of the previous expressions, which may cause discrepancies when loading tokenized files. However, the @@ is more efficient in interpreted mode since the expansion occurs in advance of execution.