factor/core/continuations/continuations.factor

! Copyright (C) 2003, 2009 Slava Pestov.
! See http://factorcode.org/license.txt for BSD license.
USING: arrays vectors kernel kernel.private sequences
namespaces make math splitting sorting quotations assocs
combinators combinators.private accessors words ;
IN: continuations

SYMBOL: error
SYMBOL: error-continuation
SYMBOL: error-thread
SYMBOL: restarts

<PRIVATE

: catchstack* ( -- catchstack )
    1 context-object { vector } declare ; inline

: >c ( continuation -- ) catchstack* push ;

: c> ( -- continuation ) catchstack* pop ;

! We have to defeat some optimizations to make continuations work
: dummy-1 ( -- obj ) f ;
: dummy-2 ( obj -- obj ) dup drop ;

: catchstack ( -- catchstack ) catchstack* clone ; inline

: set-catchstack ( catchstack -- )
    >vector 1 set-context-object ; inline

: init-catchstack ( -- ) f set-catchstack ;

PRIVATE>

TUPLE: continuation data call retain name catch ;

C: <continuation> continuation

: continuation ( -- continuation )
    datastack callstack retainstack namestack catchstack
    <continuation> ;

<PRIVATE

: >continuation< ( continuation -- data call retain name catch )
    { [ data>> ] [ call>> ] [ retain>> ] [ name>> ] [ catch>> ] } cleave ;

PRIVATE>

: ifcc ( capture restore -- )
    [ dummy-1 continuation ] 2dip [ dummy-2 ] prepose ?if ; inline

: callcc0 ( quot -- ) [ drop ] ifcc ; inline

: callcc1 ( quot -- obj ) [ ] ifcc ; inline

<PRIVATE

: (continue) ( continuation -- * )
    [
        >continuation<
        set-catchstack
        set-namestack
        set-retainstack
        [ set-datastack ] dip
        set-callstack
    ] (( continuation -- * )) call-effect-unsafe ;

PRIVATE>

: continue-with ( obj continuation -- * )
    [
        swap 4 set-special-object
        >continuation<
        set-catchstack
        set-namestack
        set-retainstack
        [ set-datastack drop 4 special-object f 4 set-special-object f ] dip
        set-callstack
    ] (( obj continuation -- * )) call-effect-unsafe ;

: continue ( continuation -- * )
    f swap continue-with ;

SYMBOL: return-continuation

: with-return ( quot -- )
    [ [ return-continuation set ] prepose callcc0 ] with-scope ; inline

: return ( -- * )
    return-continuation get continue ;

: with-datastack ( stack quot -- newstack )
    [
        [
            [ [ { } like set-datastack ] dip call datastack ] dip
            continue-with
        ] (( stack quot continuation -- * )) call-effect-unsafe
    ] callcc1 2nip ;

GENERIC: compute-restarts ( error -- seq )

<PRIVATE

: save-error ( error -- )
    dup error set-global
    compute-restarts restarts set-global ;

PRIVATE>

SYMBOL: thread-error-hook

: rethrow ( error -- * )
    dup save-error
    catchstack* empty? [
        thread-error-hook get-global
        [ (( error -- * )) call-effect-unsafe ] [ die ] if*
    ] when
    c> continue-with ;

: recover ( ..a try: ( ..a -- ..b ) recovery: ( ..a error -- ..b ) -- ..b )
    [ [ swap >c call c> drop ] curry ] dip ifcc ; inline

: ignore-errors ( quot -- )
    [ drop ] recover ; inline

: cleanup ( try cleanup-always cleanup-error -- )
    [ compose [ dip rethrow ] curry recover ] [ drop ] 2bi call ; inline

ERROR: attempt-all-error ;

: attempt-all ( ... seq quot: ( ... elt -- ... obj ) -- ... obj )
    over empty? [
        attempt-all-error
    ] [
        [
            [ [ , f ] compose [ , drop t ] recover ] curry all?
        ] { } make last swap [ rethrow ] when
    ] if ; inline

TUPLE: condition error restarts continuation ;

C: <condition> condition ( error restarts cc -- condition )

: throw-restarts ( error restarts -- restart )
    [ <condition> throw ] callcc1 2nip ;

: rethrow-restarts ( error restarts -- restart )
    [ <condition> rethrow ] callcc1 2nip ;

: throw-continue ( error -- )
    { { "Continue" t } } throw-restarts drop ;

TUPLE: restart name obj continuation ;

C: <restart> restart

: restart ( restart -- * )
    [ obj>> ] [ continuation>> ] bi continue-with ;

M: object compute-restarts drop { } ;

M: condition compute-restarts
    [ error>> compute-restarts ]
    [
        [ restarts>> ]
        [ continuation>> [ <restart> ] curry ] bi
        { } assoc>map
    ] bi append ;

<PRIVATE

: init-error-handler ( -- )
    init-catchstack
    ! VM calls on error
    [
        ! 63 = self
        63 special-object error-thread set-global
        continuation error-continuation set-global
        rethrow
    ] 5 set-special-object
    ! VM adds this to kernel errors, so that user-space
    ! can identify them
    "kernel-error" 6 set-special-object ;

PRIVATE>