an class="keyword">of</span>&nbsp;string<br>
&nbsp;&nbsp;&nbsp;&nbsp;<span class="keywordsign">|</span>&nbsp;<span class="constructor">Ptyp_arrow</span>&nbsp;<span class="keyword">of</span>&nbsp;<span class="constructor">Asttypes</span>.arg_label&nbsp;*&nbsp;<span class="constructor">Parsetree</span>.core_type&nbsp;*<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="constructor">Parsetree</span>.core_type<br>
&nbsp;&nbsp;&nbsp;&nbsp;<span class="keywordsign">|</span>&nbsp;<span class="constru