C Builder Module

assets/lua/c-builder.fnl is a C code-generation module for Fennel.

It provides:

• A factory API for building C AST nodes
• A configurable writer/formatter
• Loud failure on invalid node shapes or unsupported input

Quick Start

(local c-builder (require :c-builder))
(local C (c-builder.Factory))

(local code (C.sequence))
(code:append (C.sysinclude "stdio.h"))
(code:append (C.blank))
(code:append (C.declaration (C.function "main" "int")))

(local body (C.block))
(body:append (C.statement (C.func-call "printf" (C.str-literal "hello\\n"))))
(body:append (C.statement (C.func-return 0)))
(code:append body)

(local writer (c-builder.Writer (c-builder.Style)))
(local out (writer:write-str code))

Main API

Factory methods (C = (c-builder.Factory)):

• Structure: sequence, block, line, blank, whitespace
• Comments: line-comment, block-comment
• Directives: include, sysinclude, define, ifdef, ifndef, endif, extern
• Types/declarations: type, struct-member, struct, typedef, variable, function, declaration
• Expressions/statements: assignment, str-literal, func-call, func-return, statement

Writer methods:

• writer:write-str(sequence-or-block)
• writer:write-str-elem(element {:trim-end true|false})
• writer:write-file(sequence-or-block path)

Style

Use c-builder.Style to configure output.

Supported style enums:

• c-builder.BraceStyle (:attach, :allman, :linux)
• c-builder.PointerAlignment (:left, :right, :middle)
• c-builder.ShortFunctionStyle (:never, :empty, :inline)

Default style is tuned for common C output:

• Attached braces
• Right pointer alignment
• 4-space indentation

Initializers

Declarations support extended initializer values:

• Scalar: 1, "text", true/false
• Array-style: [1 2 3]
• Nested arrays
• Designated object-style tables:
  • {:field_1 10 :field_2 20} -> {.field_1 = 10, .field_2 = 20}

Integration with native-build

c-builder is generation-only. Use native-build to compile/run generated code:

(local c-builder (require :c-builder))
(local native-build (require :native-build))

(local C (c-builder.Factory))
(local code (C.sequence))
;; ... build code ...

(local src "generated.c")
((c-builder.Writer (c-builder.Style)):write-file code src)

(local compiler (native-build.Gcc {:standard "c11"}))
(local project (native-build.Project {:name "generated-app"
                                      :compiler compiler
                                      :build-dir "__pysembled__"}))
(project:add-executable src)
(project:build)
(project:run)

Tests

Dedicated tests are in:

• assets/lua/tests/test-c-builder.fnl

The suite includes an integration test that compiles and runs generated C via native-build.