helpful: suggests a closest variable name on unbound identifier error.

This module provides an ability to suggest a closest variable name on unbound identifier error. Simply use (require helpful) where you want this feature.

The definition of “closest” is according to the Levenshtein distance.

1 Examples

; Suggestion for a module binding

> (module test racket     (require helpful)     (define (fact x)       (cond         [(zero? x) 1]         [else (* x (fac (sub1 x)))])))

eval:1:0: fac: unbound identifier

in: fac

suggestion: do you mean `fact'?

; Suggestion for a local binding

> (module test racket     (require helpful)     (define (fact x)       (cond         [(zero? x) 1]         [else (* x (fact (sub1 y)))])))

eval:2:0: y: unbound identifier

in: y

suggestion: do you mean `x'?

; Suggestion for an imported identifier

> (module test racket     (require helpful)     (defun (fact) 1))

eval:3:0: defun: unbound identifier

in: defun

suggestion: do you mean `define'?

; No suggestion outside a module or #lang

> (require helpful)

> (let ([x 1]) y)

y: undefined;

cannot reference an identifier before its definition

in module: top-level

2 Limitations

The feature only affects code in a module or a #lang. Because top level is hopeless, the feature is disabled for the REPL.

The feature only works reliably for code at phase level 0.

3 API