Add IfZero construct to lexer + parser

src/Lexer.mll

@@ -44,6 +44,12 @@ rule entry = parse
     { PRINT }
 | "rec"
     { REC }
+| "ifzero"
+    { IFZERO }
+| "then"
+    { THEN }
+| "else"
+    { ELSE }
 | "->"
     { ARROW }
 | "="

src/Parser.mly

@@ -1,6 +1,7 @@
 %token<string> IDENT
 %token<int> INTLITERAL
 %token FUN IN LET PRINT REC
+%token IFZERO THEN ELSE
 %token ARROW EQ LPAREN RPAREN
 %token<RawLambda.binop> MULOP ADDOP
 %token EOF
@@ -67,6 +68,9 @@ any_term_:
     { Lam (x, t) }
 | LET mode = recursive x = IDENT EQ t1 = any_term IN t2 = any_term
     { Let (mode, x, t1, t2) }
+| IFZERO expr = any_term THEN tIf = any_term ELSE tElse = any_term
+    { IfZero (expr, tIf, tElse) }
+
 
 %inline any_term:
   t = placed(any_term_)