BLC

A functional, referentially transparent, untyped, interactive language based on the lambda calculus.

Syntax

Basic lambda calculus syntax, with lambda represented as a backslash. Identifiers may not be include, let, in, or =, may not contain whitespace or the characters \.#();, and additionally may not start with any of '".

Let-expressions

Let-expression are syntactic sugar for binding variables. A let-expression is of the form

let <name1> = <exp1>;
    <name2> = <exp2>;
    ...
    <nameN> = <expN>[;] in <exp>

and is equivalent to

\<name1> (\<name2> ... ((\<nameN>. <exp>) <expN>) ... <exp2>) <exp1>

Thus, because variables in lambda calculus refer to their innermost scope, variables are bound to latest definition that appears before the expression. For example,

let a = 1; b = a; a = 2 in + a b;

will evaluate to 3.

Files

Comments begin with a single hash character and continue to the end of a line.

A file is a semicolon-separated list of import statements and declarations of the form

<name> = <exp>;

Names may be redefined at any time. A name appearing in an expression refers to the the latest definition that appears before the expression (see "Execution").

Execution

The main expression is equivalent to

let <decls> in main

where let is evaluated as above. The resulting expression is applied to stdin, and should evaluate to stdout. stdin and stdout are both represented as lists of bits.