Module (scheme eval) (historical revision 43911)

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Module (scheme eval)
1. environment
2. eval

Module (scheme eval)

This module provides R7RS procedures to evaluate expressions dynamically.

This procedure returns a specifier for the environment that results by starting with an empty environment and then importing each list, considered as an import set, into it. (See section 5.6 of R7RS for a description of import sets.) The bindings of the environment represented by the specifier are immutable, as is the environment itself.

eval

[procedure] (eval EXPR-OR-DEF [ENVIRONMENT-SPECIFIER])

If EXPR-OR-DEF is an expression, it is evaluated in the specified environment and its values are returned. If it is a definition, the specified identifier(s) are defined in the specified environment, provided the environment is not immutable.

The ENVIRONMENT-SPECIFIER is optional, and if not provided it defaults to the value of (interaction-environment). This is a CHICKEN extension to R7RS, which, though strictly nonportable, is very common among Scheme implementations.

(eval '(* 7 3) (environment '(scheme base))) 
    ==> 21

(let ((f (eval '(lambda (f x) (f x x))
               (null-environment 5))))
  (f + 10))
    ==> 20

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