FILO
FILO is a stack-based programming language. A FILO program consists of a set of function definitions.
Contents
Syntax
program = definitions ;
definitions = definition, { definitions } ;
definition = identifier, "=", expression, "." ;
expression = "@" | "0" | expression, "*", expression | expression, "+", expression | expression, "-", expression | identifier, expression, "," ;
Identifiers are consecutive sequences of non-whitespace characters, excluding @, 0, *, +, -, ,, =, and .. Whitespace separates identifiers and is otherwise ignored.
*, +, and - are right-associative and have equal precedence.
A , immediately preceding a . may be omitted.
Comments begin with == and extend to the end of the line.
Expressions
Argument
@
The argument of the function.
Empty
0
An empty stack.
Push
x * y
A new stack with x pushed onto y.
Top
x + y
The top element of x unless x is empty, then y.
Pop
x - y
The stack consisting of x with its top element removed unless x is empty, then y.
Apply
f x
The result of applying function f to x.
Input/Output Encoding
How input and output are encoded is implementation-defined.
One possibility is for the argument and result to be interpreted as stacks of bits, where the each element of the stack is interpreted as 0 if it is empty, and interpreted as 1 if it is not empty, and the argument being constructed from the bits of the input, and the result being interpreted as the bits of the output.
Examples
These examples use the input/output encoding defined by the implementation below.
cat
cat=@.
Hello world
hello=h0*0. h=0*0*0*@*0*0*@*0 * @*0*@*0*0*@*@*0 * 0*0*@*@*0*@*@*0 * 0*0*@*@*0*@*@*0 *@*@*@*@*0*@*@*0 * 0*0*0*0*0*@*0*0 * @*@*@*0*@*@*@*0 * @*@*@*@*0*@*@*0 *0*@*0*0*@*@*@*0 * 0*0*@*@*0*@*@*0 * 0*0*@*0*0*@*@*0 * @*0*0*0*0*@*0*0 *0*@*0*@*0*0*0*0.
