From eb6da7644bcf0656602fdf6e43f293759c853f66 Mon Sep 17 00:00:00 2001 From: Akshay Date: Sun, 8 Nov 2020 09:52:35 +0530 Subject: add named let and simultaneous define semantics --- environment.scm | 2 ++ 1 file changed, 2 insertions(+) (limited to 'environment.scm') diff --git a/environment.scm b/environment.scm index 4917a40..37f9fa4 100644 --- a/environment.scm +++ b/environment.scm @@ -29,6 +29,7 @@ (error "Too few or too many arguments supplied" vars vals))) ;;; variable lookup +(define (is-unassigned? u) (eq? u '*unassigned*)) (define (lookup-variable-value var env) (cond [(empty-env? env) (error "Unbound variable" var)] @@ -76,5 +77,6 @@ the-empty-env)]) (define-variable! 'true #t initial-env) (define-variable! 'false #f initial-env) + (define-variable! '*unassigned* #f initial-env) initial-env)) -- cgit v1.2.3