27.2 The very dangerous “pragma” Bigloo special forms

Bigloo has a special form which allows the inclusion of C text into the produced code. It is only applicable to the C back-end. In particular, the JVM back-end (see Chapter The Java interface) does not support it.

bigloo syntax: pragma::ident string [args]

bigloo syntax: free-pragma::ident string [args]

This force Bigloo to include string in the produced C code as a regular C fragment of code. This form must not be used without an in depth understanding of Bigloo C code production; with unskilled use, the produced C file may be unacceptable to the C compiler.

Values can be passed to a pragma form, being referenced in string by expressions of the form $number. Such expression are replaced by the corresponding values, the number of referenced values in string being exactly the number of values provided. Here is an example of pragma usage:

(define (fibo x::long)
   (pragma "printf( \"fib(%d):%d\\n\", $1, $2 );" 
           x 
           (fib x)))

Arguments provided to a pragma form are not converted during compilation. Hence, pragma arguments can be of any types, including, foreign types.

A pragma result type can be specified using the notation pragma::name where the default type is unspecified. Then, for instance, the expression (pragma::bool "$1 == 0" x) will be considered to be returning a object of type bool (C boolean) while the expression (pragma "$1 == 0" x) will be considered by Bigloo to be returning the unspecified typed object.

The compiler assumes that a pragma forms operates a side effects and that it writes into its parameters. This assumption no long holds with free-pragma. This is the only difference between the two forms.

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