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Merge pull request #157 from Mingun/stack
Extract the variable stack to a separate file and test it
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,187 @@ | ||
| "use strict"; | ||
|
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| /** Utility class that helps generating code for C-like languages. */ | ||
| class Stack { | ||
| /** | ||
| * Constructs the helper for tracking variable slots of the stack virtual machine | ||
| * | ||
| * @param {string} ruleName The name of rule that will be used in error messages | ||
| * @param {string} varName The prefix for generated names of variables | ||
| * @param {string} type The type of the variables. For JavaScript there are `var` or `let` | ||
| */ | ||
| constructor(ruleName, varName, type) { | ||
| /** Last used variable in the stack. */ | ||
| this.sp = -1; | ||
| /** Maximum stack size. */ | ||
| this.maxSp = -1; | ||
| this.varName = varName; | ||
| this.ruleName = ruleName; | ||
| this.type = type; | ||
| } | ||
|
|
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| /** | ||
| * Returns name of the variable at the index `i`. | ||
| * | ||
| * @param {number} i Index for which name must be generated | ||
| * @return {string} Generated name | ||
| * | ||
| * @throws {RangeError} If `i < 0`, which means a stack underflow (there are more `pop`s than `push`es) | ||
| */ | ||
| name(i) { | ||
| if (i < 0) { | ||
| throw new RangeError( | ||
| `Rule '${this.ruleName}': The variable stack underflow: attempt to use a variable '${this.varName}<x>' at an index ${i}` | ||
| ); | ||
| } | ||
|
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| return this.varName + i; | ||
| } | ||
|
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| /** | ||
| * Assigns `exprCode` to the new variable in the stack, returns generated code. | ||
| * As the result, the size of a stack increases on 1. | ||
| * | ||
| * @param {string} exprCode Any expression code that must be assigned to the new variable in the stack | ||
| * @return {string} Assignment code | ||
| */ | ||
| push(exprCode) { | ||
| const code = this.name(++this.sp) + " = " + exprCode + ";"; | ||
|
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| if (this.sp > this.maxSp) { this.maxSp = this.sp; } | ||
|
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| return code; | ||
| } | ||
|
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| /** | ||
| * Returns name or `n` names of the variable(s) from the top of the stack. | ||
| * | ||
| * @param {number} [n=1] Quantity of variables, which need to be removed from the stack | ||
| * @return {string|string[]} Generated name(s). If `n > 1` than array has length of `n` | ||
| * | ||
| * @throws {RangeError} If the stack underflow (there are more `pop`s than `push`es) | ||
| */ | ||
| pop(n) { | ||
| if (n !== undefined) { | ||
| this.sp -= n; | ||
|
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| return Array.from({ length: n }, (v, i) => this.name(this.sp + 1 + i)); | ||
| } | ||
|
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| return this.name(this.sp--); | ||
| } | ||
|
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| /** | ||
| * Returns name of the first free variable. The same as `index(0)`. | ||
| * | ||
| * @return {string} Generated name | ||
| * | ||
| * @throws {RangeError} If the stack is empty (there was no `push`'s yet) | ||
| */ | ||
| top() { return this.name(this.sp); } | ||
|
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||
| /** | ||
| * Returns name of the variable at index `i`. | ||
| * | ||
| * @param {number} [i] Index of the variable from top of the stack | ||
| * @return {string} Generated name | ||
| * | ||
| * @throws {RangeError} If `i < 0` or more than the stack size | ||
| */ | ||
| index(i) { | ||
| if (i < 0) { | ||
| throw new RangeError( | ||
| `Rule '${this.ruleName}': The variable stack overflow: attempt to get a variable at a negative index ${i}` | ||
| ); | ||
| } | ||
|
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| return this.name(this.sp - i); | ||
| } | ||
|
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| /** | ||
| * Returns variable name that contains result (bottom of the stack). | ||
| * | ||
| * @return {string} Generated name | ||
| * | ||
| * @throws {RangeError} If the stack is empty (there was no `push`es yet) | ||
| */ | ||
| result() { | ||
| if (this.maxSp < 0) { | ||
| throw new RangeError( | ||
| `Rule '${this.ruleName}': The variable stack is empty, can't get the result'` | ||
| ); | ||
| } | ||
|
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| return this.name(0); | ||
| } | ||
|
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| /** | ||
| * Returns defines of all used variables. | ||
| * | ||
| * @return {string} Generated define variable expression with the type `this.type`. | ||
| * If the stack is empty, returns empty string | ||
| */ | ||
| defines() { | ||
| if (this.maxSp < 0) { | ||
| return ""; | ||
| } | ||
|
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| return this.type + " " + Array.from({ length: this.maxSp + 1 }, (v, i) => this.name(i)).join(", ") + ";"; | ||
| } | ||
|
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| /** | ||
| * Checks that code in the `generateIf` and `generateElse` move the stack pointer in the same way. | ||
| * | ||
| * @param {number} pos Opcode number for error messages | ||
| * @param {function()} generateIf First function that works with this stack | ||
| * @param {function()} [generateElse] Second function that works with this stack | ||
| * @return {undefined} | ||
| * | ||
| * @throws {Error} If `generateElse` is defined and the stack pointer moved differently in the | ||
| * `generateIf` and `generateElse` | ||
| */ | ||
| checkedIf(pos, generateIf, generateElse) { | ||
| const baseSp = this.sp; | ||
|
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| generateIf(); | ||
|
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| if (generateElse) { | ||
| const thenSp = this.sp; | ||
|
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| this.sp = baseSp; | ||
| generateElse(); | ||
|
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| if (thenSp !== this.sp) { | ||
| throw new Error( | ||
| "Rule '" + this.ruleName + "', position " + pos + ": " | ||
| + "Branches of a condition can't move the stack pointer differently " | ||
| + "(before: " + baseSp + ", after then: " + thenSp + ", after else: " + this.sp + ")." | ||
| ); | ||
| } | ||
| } | ||
| } | ||
|
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| /** | ||
| * Checks that code in the `generateBody` do not move stack pointer. | ||
| * | ||
| * @param {number} pos Opcode number for error messages | ||
| * @param {function()} generateBody Function that works with this stack | ||
| * @return {undefined} | ||
| * | ||
| * @throws {Error} If `generateBody` move the stack pointer (if it contains unbalanced `push`es and `pop`s) | ||
| */ | ||
| checkedLoop(pos, generateBody) { | ||
| const baseSp = this.sp; | ||
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| generateBody(); | ||
|
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| if (baseSp !== this.sp) { | ||
| throw new Error( | ||
| "Rule '" + this.ruleName + "', position " + pos + ": " | ||
| + "Body of a loop can't move the stack pointer " | ||
| + "(before: " + baseSp + ", after: " + this.sp + ")." | ||
| ); | ||
| } | ||
| } | ||
| } | ||
|
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| module.exports = Stack; |
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