String to S-expression for Fundamentals I, 2016, Northeastern University

8.16.0.4

String to S-expression for Fundamentals I, 2016, Northeastern University🔗ℹ

matthias

The teachpack provides a single function:

procedure
(string->sexpr s) → (or/c #false PD*)
s : string?

Convert the given String into an S-expression that belongs to PD*. If the function produces #false, the given String is either not an S-expression or it is an S-expression that does not belong to PD*.

; A PD* (short for picture description) is one of:
; – 'empty-image
; – String
; – (list 'circle Number String String)
; – (list 'rectangle Number Number String String)
; – (list 'beside LPD*)
; – (list 'above LPD*)
;
; An LPD* is [Listof PD*]

Examples:

> (string->sexpr "empty-image")
'empty-image
> (string->sexpr "\"nope\"")
"nope"
> (string->sexpr "(circle 10 \"solid\" \"red\")")
'(circle 10 "solid" "red")
> (string->sexpr "(rectangle 10 20 \"solid\" \"red\")")
'(rectangle 10 20 "solid" "red")
> (string->sexpr "(above (rectangle 10 20 \"solid\" \"red\"))")
#f
> (string->sexpr
"(beside \"hello\" (rectangle 10 20 \"solid\" \"red\") \"world\")")
#f
> (string->sexpr "(circle 10 solid red")
#f

Thanks to Eric L. for discovering the discrepancy between the data definition and the signature.

Changed in version 1.0 of package string-sexpr: Thu Nov 10 13:42:33 EST 2016
Changed in version 2.0: Sun Nov 13 21:53:56 EST 2016