Seven Obscure Languages in Seven Weeks

Exploring Character and String Operations

Following the tradition of the C language, a Forth character is simply an integer number optionally represented as a single-quoted literal. Characters can be subtracted, incremented, and compared, which is helpful, but they can also be added, divided, and multiplied, which is not. Forth giveth you a lot of power over characters—use it wisely. For instance, you can define a word to check if a character represents a decimal digit:

: ?DIGIT ( c -- flag ) [CHAR] 0 [CHAR] 9 1+ WITHIN ;
'a' ?DIGIT .↩ 0  ok
'7' ?DIGIT .↩ -1  ok \ True
BL ?DIGIT .↩ 0  ok

In this example, the word [CHAR] ( "name" -- n ) converts a literal into an integer number, according to the current character ...