Succeed or Fail

scheme.rkt

(define (seval sexp succeed fail env)
  (cond ((primitive? sexp) sexp)
        ((symbol? sexp) (succeed (lookup-environment env sexp) fail))
        ; Special forms
        ((define? sexp) (seval-define sexp env))
        ((if? sexp) (succeed (seval-if sexp env) fail)
        ((lambda? sexp) (succeed (seval-lambda sexp env) fail))
       
        ; Procedure application
        ((list? sexp) (sapply sexp env))
        (else (error "Bad expression")))))