diff --git a/docs/introduction/first-program.rst b/docs/introduction/first-program.rst index eb61b46ab..13c6fa914 100644 --- a/docs/introduction/first-program.rst +++ b/docs/introduction/first-program.rst @@ -343,48 +343,105 @@ you can read :doc:`../reference/surface-syntax`. Gum, Glue, and Antiquoted C ====================================================== -Next we will have to write the C code, -which does the things that |cogent| cannot do. -|cogent| code will be compiled to C code, -and is always invoked as a subroutine, by a C program. -The C programs we write for |cogent| are not plain C; -they are called *antiquoted C* (c.f. :doc:`../reference/antiquoted-c`). +At this point, +we could run the |cogent| compiler, +and we'd get some code out:: + + $ cogent -g Adder.cogent + Parsing... + Resolving dependencies... + Typechecking... + Desugaring and typing... + Normalising...ANF + Re-typing NF... + Simplifying... + Skipped + Monomorphising... + Re-typing monomorphic ASST... + Generating C code... + > Writing to file: ./Adder.h + > Writing to file: ./Adder.c + Compilation finished! + +|cogent| code is compiled to C code, +and is always invoked as a subroutine by a C program: +remember that, from |cogent| code, +many operations aren't possible, +but within the framework of a larger program, +we can build quite powerful systems. + +The compiled result is not at all pleasant to read, +nor is it especially easy to interact with. +So while we *could* pick through +the generated ``Adder.c`` and ``Adder.h``, +and work out the exact construct we need, +it's much easier to have the |cogent| compiler +help us out by generating much of +the glue needed to run our functions. + +We'll write in C --- but not *plain* C. +We write in a syntax called +`*Antiquoted C* <:doc:../reference/antiquoted-c>`_, +which lets us interface regular C constructs +with |cogent| types and functions. + +An Antiquoted C file is +very similar to a regular C file --- +indeed, it's very nearly a superset of C. +The only difference is +you may introduce *antiquotes* into the C code: +an antiquote is comprised of a name +(e.g., ``$ty``, ``$exp``, ``$esc``), +a colon, and a |cogent| snippet +enclosed by a pair of parentheses, +and these allow us to refer to +types and expressions in our programs +without needing to know +exactly what they were compiled to. +This is especially important +as the current |cogent| compiler +does not generate predictable C names; +see `issue #322 `_. + +With that in mind, +let's write some Antiquoted C. .. code-block:: c - :linenos: - :emphasize-lines: 1,3,6,9,13 - - $esc:(#include ) - $esc:(#include ) - #include "generated.c" - - int main(void){ - $ty:(U32) first_num = 19; - $ty:(U32) second_num = 2; - - $ty:((U32, U32)) args; - args.p1 = first_num; - args.p2 = second_num; - - $ty:(R U32 ()) ret = $exp:add(args); - if(ret.tag == TAG_ENUM_Success){ - $ty:(U32) sum = ret.Success; - printf("Sum is %u\n", sum); - return 0; - } else { - printf("Error: Overflow detected.\n"); - return 1; - } - } - -An antiquoted C file is very similar to a regular C file. The only -difference is that you can write *antiquotes* in the C code. An antiquote -is comprised of an antiquote name (e.g. ``$ty``, ``$exp``, -``$esc``, ``$spec``), a colon, and a |cogent| snippet enclosed by a pair of parentheses. -The purpose of having antiquotes is that you can refer to |cogent| types, expressions, etc. -without knowing what they get compiled to. In particular, with the current implementation of -the |cogent| compiler, it's very difficult to know what C names will be generated. See -`ticket #322 `_ on GitHub. + + int main (void) + { + return 0; + } + + +.. code-block:: c + :linenos: + :emphasize-lines: 1,3,6,9,13 + + $esc:(#include ) + $esc:(#include ) + #include "generated.c" + + int main (void) + { + $ty:(U32) first_num = 19; + $ty:(U32) second_num = 2; + + $ty:((U32, U32)) args; + args.p1 = first_num; + args.p2 = second_num; + + $ty:(R U32 ()) ret = $exp:add(args); + if (ret.tag == TAG_ENUM_Success) { + $ty:(U32) sum = ret.Success; + printf("Sum is %u\n", sum); + return 0; + } else { + printf("Error: Overflow detected.\n"); + return 1; + } + } + Let's first look at the ``main`` function. In line 6, the antiquote ``$ty:(U32)`` means that we want to use a ``U32`` (a primitive type in |cogent|) equivalent in C. On line 9,