Learn Resid

Resid is a statically typed, compiled language whose compiler is obliged to compute everything it can prove before it emits code. A program is reduced, step by step, until only computation that truly depends on runtime information is left. That remainder, the residual program, is what your binary runs.

This book is a tour. Each chapter builds on the previous one, and every complete example on these pages is compiled and run by the documentation build, with its output checked, so what you read is what the compiler does.

The ideas in one page

• Values are immutable. A binding never changes, and nothing can be reassigned or shadowed. Lists, maps and strings are values too; the compiler updates them in place only when it can prove no one else sees the old version.
• Everything starts out compile-time. A call whose arguments are known is evaluated while compiling. A call with some known arguments is specialized. Runtime work enters only through unknown inputs: arguments, files, the network, rt.
• Authority is explicit. A function that reads files, runs processes or opens sockets declares it with @requires(...), and so does every function that calls it, all the way up to main.
• Numbers are exact about their width. Int(8) through Int(512), UInt(...), Float(16) through Float(128) and decimal Dec(N). All arithmetic is checked; nothing overflows or truncates silently.
• Behaviors instead of interfaces. How a type is ordered or printed is a value you name (Ord(Point) = { .compare = by_x, .least = lo, .greatest = hi };), not an interface it implements.

Install the compiler

Your first program