Opened 2 weeks ago

#1563 new defect

Renaming issue with "the"

Reported by: megane Owned by:
Priority: major Milestone: 5.1
Component: expander Version: 5.0.0
Keywords: er-macro-transformer scrutinizer Cc:
Estimated difficulty:

Description

The first argument to ##core#the should be the validated type as
returned by check-and-validate-type. In the validated type all type
variables have been replaced with gensymed new names.

Here's the code for the the macro in its entirety:

(##sys#extend-macro-environment
 'the '()
 (##sys#er-transformer
  (lambda (x r c)
    (##sys#check-syntax 'the x '(_ _ _))
    (if (not (memq #:compiling ##sys#features))
	(caddr x)
	`(##core#the ,(chicken.compiler.scrutinizer#check-and-validate-type (cadr x) 'the)
		     #t
		     ,(caddr x))))))

Add a debug print to check-and-validate-type to confirm typevariables are being renamed:

(define (check-and-validate-type type loc #!optional name)
  (let-values (((t pred pure) (validate-type (strip-syntax type) name)))
   (when t (dd "type validated ~a => ~a" type t)) ; <- new line
    (or t 
	(error loc "invalid type specifier" type))))

Now try this example:

(import (chicken type))
(compiler-typecase (the (forall (a) (pair symbol a)) (pair 'sym 1))
  ((forall (a) (pair a fixnum)) 1))

This should compile without errors. One a should unify with symbol
and the other with fixnum.

Instead of that you get the error:

Error: at toplevel:
  (que.scm:20) no clause applies in `compiler-typecase' for expression of type `(forall (a) (pair symbol a))':
    (forall (a) (pair a fixnum))

If you check the debug output for scrutinizer you can see that both
a's have actually the same name! (You can try renaming one pair of
as to see it indeed compiles without errors.)

You can see check-and-validate-type correctly renamed the variables:

[debug|0] type validated (forall (a) (pair a fixnum)) => (forall (a18) (pair a18 fixnum))
[debug|0] type validated (forall (a) (pair symbol a)) => (forall (a20) (pair symbol a20))

But if you check the canonicalized form you see:

$ csc -debug 2 -O3 que.scm
[canonicalized]
(##core#callunit library)

(##core#callunit eval)

(##core#callunit expand)

(##core#undefined)

(##core#undefined)

(##core#undefined)

(##core#undefined)

(##core#undefined)

(let ((g1719 (##core#the (forall (a) (pair symbol a)) #t (pair 'sym '1)))) <--- no renaming here!
  (##core#typecase "que.scm:20" g1719 ((forall (a) (pair a fixnum)) '1)))

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