Text Entry

Text can be typed at any time. For example, we now enter identifiers into the Boolean expression so that it reads:

(X or Y) and Z

The following assumes that the structural selection is at the first <expression> placeholder within the Boolean expression:

( <expression> or <expression> ) and <expression>

If this is not the case, move it there by clicking within the first <expression>.

Whenever you type text, just use lower case letters and ignore formatting. After syntactic analysis, if there are no syntax errors, what you have typed will be prettyprinted. For example, depending on the settings of style resources and enforcement parameters, keywords may be in boldface and identifiers in upper case.

Type

x

and then strike the RETURN key.

The X is inserted and the structural selection is advanced to the next <expression> placeholder.

Type

y+

(an intentional syntax error), and then strike RETURN.

The syntax error is detected, the error message is issued in the status-pane, and instead of advancing to the next placeholder, the insertion cursor is positioned near the syntax error.

Commands to delete individual characters are standard. To erase the character before the insertion cursor, use command delete-previous-character (key: Backspace). To erase the character after the insertion cursor, use command delete-next-character (X: Delete or ^D   NT: Delete).

Delete the + sign, and then strike RETURN.

The syntax error has been corrected, so the structural selection is advanced to the next <expression> placeholder. We now illustrate that syntax errors need not be corrected immediately.

Type

z+

(another intentional syntax error), and then strike RETURN.

As before, the syntax error is detected and the error message is issued.

Strike RETURN without modifying the expression.

Because there has been no change since the syntax error message was issued, striking RETURN this time overrides the syntax error and advances the structural selection, leaving the erroneous phrase in place. You can return at any time to correct syntax errors. The erroneous phrase will remain displayed in a distinctive style until the error is corrected.

Click the mouse to position the insertion cursor at the spurious + sign delete it. Then strike the RETURN key.

The structural selection is advanced to the <statement> placeholder within the conditional statement.

If the insertion cursor is within a selected region of text, deleting a character deletes the entire selection. Similarly, if the insertion cursor is within a selected region of text, inserting a character first deletes the selected characters.

Drag the mouse over the entire expression

(X or Y) and Z

so that it is highlighted. Then strike Backspace.

The entire subexpression is deleted.

Now retype

(x or y) and z

and then strike RETURN.

The structural selection is positioned at a <statement> placeholder in a context in which a list of statements is permitted.

Type

a:=1;b:=2;c:=p and q and r;

and then strike RETURN.

Note that the statements are prettyprinted one per line, with whitespace around the operators. The structural selection is again positioned at a <statement> placeholder.

Type

d:=123456789;e:=12345.6789e12;

and then strike RETURN.

Note that numbers are prettyprinted in a standard format (e.g., with underscores separating groups of three digits). The structural selection is again positioned at a <statement> placeholder.

Type

f:=((x+y)*(z));

and then strike RETURN.

Note that expressions are prettyprinted in a standard format (e.g., with redundant parentheses eliminated). The structural selection is again positioned at a <statement> placeholder.