Execution

The typed IR is one thing shared by the interpreter and the compiled binary; this section is what that sharing promises a reader: the order code runs in, what a copy costs, what recursion is guaranteed, what cleanup is, and which arm of a branch on the target is compiled at all.

What belongs here#

What does not belong here: memory as a topic in general, which stays inside CONCEPT.md's own execution model outside what a program can observe. Every page in this folder is a reference page: an example first, then the syntax, then numbered rules, then what the construct is not.

Pages#

• Loops - for walks an Iterate, while repeats while a condition holds, and loop is the endless one - with the type Never until a break gives it a Void. while true is an error, because never ending is a property of the syntax here.
• Evaluation order - Evaluation order is source order - the receiver first, then the arguments as they are written, then the parameter defaults - so a side effect in an argument is exactly as predictable as reading the line.
• What a copy costs - A copy always behaves the same way, but what it costs depends on the shape of the type - inline for a small fixed-size value, copy-on-write for heap-backed storage, and never for a shared type.
• Tail calls and stack overflow - Direct self-recursion in tail position is guaranteed to run without growing the stack, and every other call uses a frame of its task's stack; a recursion that runs out of stack panics with stack overflow instead of crashing.
• Destructors - close() runs at the last release - A shared type's close() is its destructor - it runs exactly once at the last release, user code never calls it, and a binding that holds one is released at the end of its block, the last declared first.
• Compile-time branches - A match, an if or an if const whose subject is a compile-time constant keeps the one arm its value selects - OperatingSystem.current is one - while every arm is still type checked on every machine and exhaustiveness is judged by the type.