1 files changed, 77 insertions, 0 deletions
diff --git a/godel/grammar.peg b/godel/grammar.peg
new file mode 100644
index 0000000..a66d5a5
--- /dev/null
+++ b/godel/grammar.peg
@@ -0,0 +1,77 @@
+Program = lines: (ProgramInstruction / (_/[\n]))* {
+  return { instructions: lines.filter((line) => typeof line !== "string" || line.trim() != "") };
+}
+
+ProgramInstruction = _? instruction: (LabeledInstruction / Instruction) _? [\n]? {
+  let x = 0;
+  let y = 0;
+  if (instruction.label) {
+    x = instruction.label.godel;
+    y = instruction.instruction.godel;
+  } else {
+    y = instruction.godel;
+  }
+  return { instruction, godel: ((2 ** x) * ((2 * y) + 1) - 1) };
+}
+
+LabeledInstruction = label:Label _ instruction:Instruction {
+  return { label, instruction };
+}
+
+Label = "[" _? label:LABEL_V _? "]" {
+  return label;
+}
+  
+Instruction = conditional: Conditional { return { conditional, godel: conditional.godel }; } 
+  / assignment: Assignment { return { assignment, godel: assignment.godel }; }
+  / goto: Goto { return { goto, godel: goto.godel }; }
+
+Goto = GOTO _ label: LABEL_V {
+  return { label, godel: label.godel + 2 };
+}
+
+Conditional = "IF" _ variable: VAR  _? "!=" _? "0" _ goto: Goto {
+  const y = variable.godel - 1;
+  const x = goto.godel;
+  return { variable, goto, godel: ((2 ** x) * ((2 * y) + 1) - 1) };
+}
+
+Assignment = variable: VAR _ "<-" _ expr: Expression {
+  if (expr.left.symbol != variable.symbol) {
+    error("left hand variable must match right hand");
+  }
+  const x = expr.instructionNumber;
+  const y = variable.godel - 1;
+  return { variable, expr, godel: ((2 ** x) * ((2 * y) + 1) - 1) };
+}
+
+Expression = left: VAR _ opr: OPERATION _ "1" {
+  const instructionNumber = { "+" : 1, "-" : 2 }[opr];
+  return { left, opr, instructionNumber };
+} / left: VAR  {
+  return { left, instructionNumber: 0 };
+}
+
+VAR = symbol:"Y" { return { symbol, godel: 1 }; } / symbol:("X" / "Z") ind:Integer+ {
+  const index = parseInt(ind);
+  const order = ["X", "Z"];
+  const godel = index * order.length + order.indexOf(symbol);
+  return { symbol: symbol + ind, godel };
+}
+
+GOTO = "GOTO"
+
+OPERATION = "+" / "-"
+
+LABEL_V = symbol:END_LABEL { return symbol } / symbol:[A-E] ind:Integer+ {
+  const index = parseInt(ind);
+  const godel = (symbol.charCodeAt(0) - "A".charCodeAt(0) + 1) + 5*(index-1);
+  return { symbol: symbol + ind, godel };
+}
+
+END_LABEL = "E1"
+
+Integer "integer"
+  = [0-9]+ { return parseInt(text(), 10); }
+
+_ "whitespace" = [ \t]+ {  }