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6.25.1.1 Stack Capture

A Scheme program can use the make-stack primitive anywhere in its code, with first arg #t, to construct a Scheme value that describes the Scheme stack at that point.

(make-stack #t)
⇒
#<stack 25205a0>

Use start-stack to limit the stack extent captured by future make-stack calls.

Scheme Procedure: make-stack obj arg …
C Function: scm_make_stack (obj, args)

Create a new stack. If obj is #t, the current evaluation stack is used for creating the stack frames, otherwise the frames are taken from obj (which must be a continuation or a frame object).

arg … can be any combination of integer, procedure, prompt tag and #t values.

These values specify various ways of cutting away uninteresting stack frames from the top and bottom of the stack that make-stack returns. They come in pairs like this: (inner_cut_1 outer_cut_1 inner_cut_2 outer_cut_2 …).

Each inner_cut_i can be #t, an integer, a prompt tag, or a procedure. #t means to cut away all frames up to but excluding the first user module frame. An integer means to cut away exactly that number of frames. A prompt tag means to cut away all frames that are inside a prompt with the given tag. A procedure means to cut away all frames up to but excluding the application frame whose procedure matches the specified one.

Each outer_cut_i can be an integer, a prompt tag, or a procedure. An integer means to cut away that number of frames. A prompt tag means to cut away all frames that are outside a prompt with the given tag. A procedure means to cut away frames down to but excluding the application frame whose procedure matches the specified one.

If the outer_cut_i of the last pair is missing, it is taken as 0.

Scheme Syntax: start-stack id exp

Evaluate exp on a new calling stack with identity id. If exp is interrupted during evaluation, backtraces will not display frames farther back than exp’s top-level form. This macro is a way of artificially limiting backtraces and stack procedures, largely as a convenience to the user.


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