eval

The (rnrs eval (6))library allows a program to create Scheme expressions as data at run time and evaluate them.

(eval expression environment)procedure 

Evaluates expression in the specified environment and returns its value. Expression must be a syntactically valid Scheme expression represented as a datum value, and environment must be an environment, which can be created using the environment procedure described below.

If the first argument to eval is determined not to be a syntactically correct expression, then eval must raise an exception with condition type &syntax. Specifically, if the first argument to eval is a definition or a splicing begin form containing a definition, it must raise an exception with condition type &syntax.

(environment import-spec ...)procedure 

Import-spec must be a datum representing an <import spec> (see report section on “Library form”). The environment procedure returns an environment corresponding to import-spec.

The bindings of the environment represented by the specifier are immutable: If eval is applied to an expression that is determined to contain an assignment to one of the variables of the environment, then eval must raise an exception with a condition type &syntax.

(library (foo)

  (export)

  (import (rnrs)

          (rnrs eval))

  (write

    (eval '(let ((x 3)) x)

          (environment '(rnrs))))) 
  writes 3

(library (foo)

  (export)

  (import (rnrs)

          (rnrs eval))

  (write

    (eval

      '(eval:car (eval:cons 2 4))

      (environment

        '(prefix (only (rnrs) car cdr cons null?)

                 eval:))))) 
  writes 2