factor/library/inference/branches.factor

! :folding=indent:collapseFolds=1:

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! Copyright (C) 2004 Slava Pestov.
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IN: inference
USE: combinators
USE: dataflow
USE: errors
USE: interpreter
USE: kernel
USE: lists
USE: logic
USE: math
USE: namespaces
USE: stack
USE: strings
USE: vectors
USE: words
USE: hashtables

: infer-branch ( quot -- [ in-d | datastack ] dataflow )
    #! Infer the quotation's effect, restoring the meta
    #! interpreter state afterwards.
    [
        copy-interpreter
        dataflow-graph off
        (infer)
        d-in get meta-d get cons
        get-dataflow
    ] with-scope ;

: difference ( [ in | stack ] -- diff )
    #! Stack height difference of infer-branch return value.
    uncons vector-length - ;

: balanced? ( list -- ? )
    #! Check if a list of [ in | stack ] pairs has the same
    #! stack height.
    [ difference ] map all=? ;

: max-vector-length ( list -- length )
    [ vector-length ] map [ > ] top ;

: unify-lengths ( list -- list )
    #! Pad all vectors to the same length. If one vector is
    #! shorter, pad it with unknown results at the bottom.
    dup max-vector-length swap [ dupd ensure nip ] map nip ;

: unify-result ( obj obj -- obj )
    #! Replace values with unknown result if they differ,
    #! otherwise retain them.
    2dup = [ drop ] [ 2drop gensym ] ifte ;

: unify-stacks ( list -- stack )
    #! Replace differing literals in stacks with unknown
    #! results.
    uncons [ [ unify-result ] vector-2map ] each ;

: unify ( list -- )
    #! Unify meta-interpreter state from two branches.
    dup balanced? [
        unzip
        unify-lengths unify-stacks meta-d set
        [ > ] top d-in set
    ] [
        "Unbalanced branches" throw
    ] ifte ;

: recursive-branch ( quot -- ? )
    #! Set base case if inference didn't fail.
    [
        car infer-branch drop recursive-state get set-base t
    ] [
        [ drop f ] when
    ] catch ;

: infer-branches ( branchlist instruction -- )
    #! Recursive stack effect inference is done here. If one of
    #! the branches has an undecidable stack effect, we set the
    #! base case to this stack effect and try again.
    swap f over [ recursive-branch or ] each [
        [ [ car infer-branch , ] map ] make-list swap
        >r dataflow, drop r> unify
    ] [
        current-word no-base-case
    ] ifte ;

: infer-ifte ( -- )
    #! Infer effects for both branches, unify.
    3 ensure-d
    \ drop CALL dataflow, drop pop-d
    \ drop CALL dataflow, drop pop-d 2list
    IFTE
    pop-d drop ( condition )
    infer-branches ;

: vtable>list ( [ vtable | rstate ] -- list )
    #! generic and 2generic use vectors of words, we need lists
    #! of quotations. Filter out no-method. Dirty workaround;
    #! later properly handle throw.
    unswons vector>list [
        dup \ no-method = [ drop f ] [ unit over cons ] ifte
    ] map [ ] subset nip ;

: infer-generic ( -- )
    #! Infer effects for all branches, unify.
    2 ensure-d
    \ drop CALL dataflow, drop pop-d vtable>list
    GENERIC
    peek-d drop ( dispatch )
    infer-branches ;

: infer-2generic ( -- )
    #! Infer effects for all branches, unify.
    3 ensure-d
    \ drop CALL dataflow, drop pop-d vtable>list
    2GENERIC
    peek-d drop ( dispatch )
    peek-d drop ( dispatch )
    infer-branches ;

\ ifte [ infer-ifte ] "infer" set-word-property

\ generic [ infer-generic ] "infer" set-word-property
\ generic [ 2 | 0 ] "infer-effect" set-word-property

\ 2generic [ infer-2generic ] "infer" set-word-property
\ 2generic [ 3 | 0 ] "infer-effect" set-word-property