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Case Sensitivity

Problem

This recipe gives solutions for dealing with case insensitive code in a case sensitive language and vice versa.

Introduction

The PLT languages are by default case sensitive. In a case sensitive language x and X are different names, and in a case insensitive language they are the same.

; In a case sensitive language
> (let ((x 1))
    (let ((X 2))
       x))
1
> 'X
X

; In a case insensitive language
> (let ((x 1))
    (let ((X 2))
       x))
2
> 'X
x

The trend among implementations is to use case sensitivity as default and have an option to invoke case insensitivity. The new R6RS will require case sensitivity as default.

Choosing the sensitivity in DrScheme

In DrScheme the default (except for the R5RS language) is case sensitivity. To change the sensitivity in a given buffer: in the "Language" menu choose the menu item "Choose Language", click at the button "Show Details". A tick in "Case sensitive" makes the language case sensitive and no tick makes the language case insensitive.

Choosing the sensitivity in MzScheme

Invoke MzScheme with the flags --case-sens and --case-insens to make it case sensitive or case case insensitive (or use the shorter -g and -G respectively).

Choosing case sensitivity in a per s-exp level

Use #ci or #cs to control the case sensitivity for a single s-expr.

; In a case insensitive language
> #ci(let ((x 1))
       (let ((X 2))
         x))
2

; In a case sensitive language
> #cs(let ((x 1))
       (let ((X 2))
          x))
1

Note: The advantage of using #cs and #ci is that a user of your code does not have to change settings in either DrScheme or MzScheme.

Case sensitivity of the reader

At runtime a program can use read to read in s-exps. The sensitivity of the reader is controlled by the parameter read-case-sensitive. Use (read-case-sensitive #t) and (read-case-sensitive #f) to turn sensitivity on and off.

Comments about this recipe

Contributors

-- JensAxelSoegaard - 07 Jul 2005