Embeddable Scheme Interpreter
This is a tiny embeddable implementation of a strongly-typed case-sensitive Scheme dialect.
Its main advantage is that it's small (less than 1000 lines of C code) and easily extendable. It also has more friendly error reporting than most other interpreters (see the Examples section below).
Implemented built-in primitives include:
length, list-ref, list-tail, sin, cos, tan, asin, acos, atan, ceiling, floor, truncate, round, abs, sqrt, exp, log, expt, min, max, gcd, map, reduce.
Current version is 0.9 (not yet recommended for production use) and is licensed under the 3-clause BSD license. The only prerequisite is the Boehm-Demers-Weiser GC library.
(define fib (lambda (n) (if (< n 2) n (+ (fib (- n 1)) (fib (- n 2)))))) (display (map fib '(1 2 3 4 5 6 7 8 9 10))) (newline)Output:
$ ./scheme test/fibmap.scm (1 1 2 3 5 8 13 21 34 55)
Error reportingHelpful error messages:
> (define a (= #g #t)) SYNTAX ERROR: Line 1: Invalid constant, expected 't' or 'f': (define a (= #g #t)) ^Checking the number of arguments to a function or primitive:
> (+ 1) RUNTIME ERROR: Line 1: Too few arguments for '+' given, expected at least 2: (+ 1) ^Also works for custom lambdas:
> (define a (lambda (n1 n2) (+ n1 n2 1))) #<lambda> > (a 1) RUNTIME ERROR: Line 1: Expected 2 arguments to lambda, 1 given: (a 1) ^It can also do argument type checking for built-in primitives:
> (expt "Hello" 2) RUNTIME ERROR: Line 1: Incorrect type for 1st argument of 'expt', number expected: (expt "Hello" 2) ^
scheme-0.9.tar.bz2 (11947 bytes, MD5: 89f92047eb2fa2962f363c8dac9d2d56)