71 lines
1.5 KiB
Factor
71 lines
1.5 KiB
Factor
USING: arrays assocs io kernel math namespaces
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prettyprint sequences strings vectors words accessors ;
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IN: turing
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! A turing machine simulator.
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TUPLE: state sym dir next ;
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! Mapping from symbol/state pairs into new-state tuples
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SYMBOL: states
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! Halting state
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SYMBOL: halt
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! This is a simple program that outputs 5 1's
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H{
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{ { 1 0 } T{ state f 1 1 2 } }
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{ { 2 0 } T{ state f 1 1 3 } }
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{ { 3 0 } T{ state f 1 -1 1 } }
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{ { 1 1 } T{ state f 1 -1 2 } }
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{ { 2 1 } T{ state f 1 -1 3 } }
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{ { 3 1 } T{ state f 1 -1 halt } }
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} states set
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! Current state
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SYMBOL: state
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! Initial state
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1 state set
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! Position of head on tape
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SYMBOL: position
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! Initial tape position
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5 position set
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! The tape, a mutable sequence of some kind
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SYMBOL: tape
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! Initial tape
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20 0 <array> >vector tape set
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: sym ( -- sym )
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! Symbol at head position.
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position get tape get nth ;
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: set-sym ( sym -- )
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! Set symbol at head position.
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position get tape get set-nth ;
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: next-state ( -- state )
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! Look up the next state/symbol/direction triplet.
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state get sym 2array states get at ;
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: turing-step ( -- )
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! Do one step of the turing machine.
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next-state
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dup sym>> set-sym
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dup dir>> position [ + ] change
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next>> state set ;
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: c ( -- )
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! Print current turing machine state.
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state get .
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tape get .
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2 position get 2 * + CHAR: \s <string> write "^" print ;
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: n ( -- )
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! Do one step and print new state.
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turing-step c ;
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