1. A method in a computer system for determining an operand for an operator during data entry of the nodes of an intentional program tree, the method comprising: receiving a sequence of tokens, each token indicating a computational construct corresponding to a node of the intentional program tree; when receiving an indication of a selection of a subtree of the intentional program tree, selecting the indicated subtree; and when receiving an indication of a next token to be appended to the sequence of tokens, when a subtree is currently selected, identifying the selected subtree as an operand of the operator represented by the next token; when a subtree is not currently selected, identifying according to predefined rules of operator precedence an operand of the operator represented by the next token; and adding a node to the intentional program tree indicating the operator represented by the next token and indicating the identified operand whereby predefined rules of operator precedence may be overridden by selection of a subtree.