Qi (programming Language) - Core Language

Core Language

The Qi core language is a simplification of the Lisp language. Functions are written in prefix form. Symbols, variables, booleans, numbers, strings and characters are all self-evaluating if typed at the top level. Here are some examples.

Here is the traditional Hello world program in Qi:

(output "Hello, world~%")

Lists are constructed with with spaces separating the elements of the list.

A factorial function using pattern matching:

(define factorial 0 -> 1 N -> (* N (factorial (- N 1))))

A lambda function in Qi that multiplies its input by 2.

(/. X (* X 2))

The membership function using pattern-matching over lists. (Qi largely follows the Edinburgh syntax convention for matching (i.e. variables are headed in uppercase), except that spaces are used instead of commas to separate items.)

(define member _ -> false X -> true X -> (member X Y))

A function using guards that finds the first number greater than N in a list.

(define find_greater N -> (error "no number greater than ~A.~%" N) N -> M where (> M N) N -> (find_greater N Ns))