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Chapter 12: Extending GNU make 133

12 Extending GNU make

GNU make provides many advanced capabilities, including many useful functions. However,

it does not contain a complete programming language and so it has limitations. Sometimes

these limitations can be overcome through use of the shell function to invoke a separate

program, although this can be ineﬃcient.

In cases where the built-in capabilities of GNU make are insuﬃcient to your requirements

there are two options for extending make. On systems where it’s provided, you can utilize

GNU Guile as an embedded scripting language (see Section 12.1 [GNU Guile Integration],

page 133). On systems which support dynamically loadable objects, you can write your

own extension in any language (which can be compiled into such an object) and load it to

provide extended capabilities (see Section 12.2.1 [The load Directive], page 136).

12.1 GNU Guile Integration

GNU make may be built with support for GNU Guile as an embedded extension language.

Guile implements the Scheme language. A review of GNU Guile and the Scheme language

and its features is beyond the scope of this manual: see the documentation for GNU Guile

and Scheme.

You can determine if make contains support for Guile by examining the .FEATURES

variable; it will contain the word guile if Guile support is available.

The Guile integration provides one new make function: guile. The guile function takes

one argument which is ﬁrst expanded by make in the normal fashion, then passed to the

GNU Guile evaluator. The result of the evaluator is converted into a string and used as the

expansion of the guile function in the makeﬁle.

In addition, GNU make exposes Guile procedures for use in Guile scripts.

12.1.1 Conversion of Guile Types

There is only one “data type” in make: a string. GNU Guile, on the other hand, provides

a rich variety of diﬀerent data types. An important aspect of the interface between make

and GNU Guile is the conversion of Guile data types into make strings.

This conversion is relevant in two places: when a makeﬁle invokes the guile function

to evaluate a Guile expression, the result of that evaluation must be converted into a make

string so it can be further evaluated by make. And secondly, when a Guile script invokes

one of the procedures exported by make the argument provided to the procedure must be

converted into a string.

The conversion of Guile types into make strings is as below:

#f False is converted into the empty string: in make conditionals the empty string

is considered false.

#t True is converted to the string ‘#t’: in make conditionals any non-empty string

is considered true.

symbol

number A symbol or number is converted into the string representation of that symbol

or number.

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