concepts/Primitive-functions.md

+
+# Primitive functions 
+
+Primitive functions are the basic building blocks of the SaC language. 
+The idea is that the standard library should be built on top of these functions.
+This way anyone can implement their own standard library or use the functions directly and popular symbols like + will not have their meaning set in stone.
+
+But how do these primitive functions work?
+
+I have not found a definitive list of primitive functions.
+The best I could find is in the `sac2c` source code in the [`src/libsac2c/tree/prf_info.mac` file](https://gitlab.sac-home.org/sac-group/sac2c/-/blob/develop/src/libsac2c/tree/prf_info.mac).
+
+Here the primitive functions are defined as a list of macros. 
+But these are not their actual names. 
+For instance the following definition:
+
+```c
+  PRF (and_SxS, (PA_S, PA_S, PA_x), 2, AND, NTCCTprf_log_op_SxS, COand, COMPprfOp_SxS,
+       SCSprf_and_SxS, NULL, NULL, SAAdim_is_0, SAAshp_is_empty, NULL, 0, PPIgetPVSxS,
+       ICCnone, TEone, NULL, NULL),
+```
+
+It defines the `and` function. 
+Importantly the `SxS` part means that the function takes two arguments of type `S` which stands for scalar.
+
+As such you also have an `and_SxV` function which takes a scalar and a vector and an `and_VxV` function which takes a vector and another vector.
+
+If you actually want to use a primitive function however you have to write it like this: `_and_SxS_()`. 
+So note how you have to add the underscores to the start and end. 
+
+In the file I linked there is this useful comment which explains the different fields in the PRF macro.
+
+---
+
+In the end of compilation there are mostly just the primitive functions left.
+These are turned into [intermediate code macros (icm)](./Intermediate-Code-Macros) in the `cg:cpl` traversal.
+These icm are then expanded into the actual code by the c preprocessor.