95 lines
3.0 KiB
JavaScript
95 lines
3.0 KiB
JavaScript
// Functions
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(function(baselib) {
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var exports = {};
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baselib.functions = exports;
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// Function types: a function is either a Primitive or a Closure.
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// A Primitive is a function that's expected to return. It is not
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// allowed to call into Closures. Its caller is expected to pop off
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// its argument stack space.
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//
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// A Closure is a function that takes on more responsibilities: it is
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// responsible for popping off stack space before it finishes, and it
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// is also explicitly responsible for continuing the computation by
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// popping off the control stack and doing the jump. Because of this,
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// closures can do pretty much anything to the machine.
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// A closure consists of its free variables as well as a label
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// into its text segment.
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var Closure = function(label, arity, closedVals, displayName) {
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this.label = label; // (MACHINE -> void)
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this.arity = arity; // number
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this.closedVals = closedVals; // arrayof number
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this.displayName = displayName; // string
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};
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// Finalize the return from a closure. This is a helper function
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// for those who implement Closures by hand.
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//
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// If used in the body of a Closure, it must be in tail
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// position. This finishes the closure call, and does the following:
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//
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// * Clears out the existing arguments off the stack frame
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// * Sets up the return value
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// * Jumps either to the single-value return point, or the multiple-value
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// return point.
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//
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// I'd personally love for this to be a macro and avoid the
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// extra function call here.
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var finalizeClosureCall = function(MACHINE) {
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MACHINE.callsBeforeTrampoline--;
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var frame, i, returnArgs = [].slice.call(arguments, 1);
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// clear out stack space
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// TODO: replace with a splice.
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for(i = 0; i < MACHINE.argcount; i++) {
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MACHINE.env.pop();
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}
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if (returnArgs.length === 1) {
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MACHINE.val = returnArgs[0];
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frame = MACHINE.control.pop();
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return frame.label(MACHINE);
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} else if (returnArgs.length === 0) {
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MACHINE.argcount = 0;
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frame = MACHINE.control.pop();
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return frame.label.multipleValueReturn(MACHINE);
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} else {
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MACHINE.argcount = returnArgs.length;
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MACHINE.val = returnArgs.shift();
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// TODO: replace with a splice.
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for(i = 0; i < MACHINE.argcount - 1; i++) {
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MACHINE.env.push(returnArgs.pop());
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}
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frame = MACHINE.control.pop();
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return frame.label.multipleValueReturn(MACHINE);
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}
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};
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var makePrimitiveProcedure = function(name, arity, f) {
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f.arity = arity;
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f.displayName = name;
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return f;
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};
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//////////////////////////////////////////////////////////////////////
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exports.Closure = Closure;
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exports.finalizeClosureCall = finalizeClosureCall;
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exports.makePrimitiveProcedure = makePrimitiveProcedure;
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})(this['plt'].baselib); |