Editing Tiny BASIC (section)

===Formal grammar===
The grammar is listed below in [[Backus–Naur form]], almost exactly as it was specified in the Design Note.<ref>{{cite magazine |title=Build Your Own BASIC |first=Dennis |last=Allison |magazine=Dr. Dobb's Journal |volume=1 |number=1 |date=1976 |url=https://archive.org/details/dr_dobbs_journal_vol_01/page/n9 |page=9}}</ref> In the listing, an asterisk ("<code>*</code>") denotes zero or more of the object to its left{{snd}} except for the first asterisk in the definition of "<code>term</code>", which is the multiplication operator; parentheses group objects; and an epsilon ("<code>ε</code>") signifies the empty string. As is common in computer language grammar notation, the vertical bar ("<code>|</code>") distinguishes alternatives, as does their being listed on separate lines. The symbol "<code>CR</code>" denotes a [[carriage return]] (usually generated by a keyboard's "Enter" key). A BREAK from the console will interrupt execution of the program.
<!-- Note: there might be some typos in the listing, which IIRC is an exact copy of the DrD original. A correction of those errors would have to be shown with (foot)notes, so that the reader will be presented with the original text as printed in the DrD. --Wernher        -->
<syntaxhighlight lang="abnf">
    line ::= number statement CR | statement CR
 
    statement ::= PRINT expr-list
                  IF expression relop expression THEN statement
                  GOTO expression
                  INPUT var-list
                  LET var = expression
                  GOSUB expression
                  RETURN
                  CLEAR
                  LIST
                  RUN
                  END
 
    expr-list ::= (string|expression) (, (string|expression) )*
 
    var-list ::= var (, var)*
 
    expression ::= (+|-|ε) term ((+|-) term)*
 
    term ::= factor ((*|/) factor)*
 
    factor ::= var | number | (expression)
 
    var ::= A | B | C ... | Y | Z
 
    number ::= digit digit*
 
    digit ::= 0 | 1 | 2 | 3 | ... | 8 | 9
 
    relop ::= < (>|=|ε) | > (<|=|ε) | =

    string ::= " ( |!|#|$ ... -|.|/|digit|: ... @|A|B|C ... |X|Y|Z)* "
</syntaxhighlight>

Note that string wasn't defined in the Design Note.

This syntax, as simple as it was, added one innovation: {{code|GOTO}} and {{code|GOSUB}} could take an expression rather than just a line number, providing an [[Goto#Computed GOTO and Assigned GOTO|assigned GOTO]]<ref>{{cite magazine |title=Quick Reference Guide for Tiny BASIC |first=Dennis |last=Allison |magazine=Dr. Dobb's Journal |volume=1 |number=1 |date=1976 |url=https://archive.org/details/dr_dobbs_journal_vol_01/page/n6 |page=6}}</ref> rather than the [[switch statement]] of the {{code|GOTO/GOSUB ... OF ...}}, a structure then supported in [[HP Time-Shared BASIC]] and predating {{code|ON ... GOTO}}. The syntax allowing {{code|IF-THEN statement}} (as opposed to just a line number to branch to) was not yet supported in Dartmouth BASIC at this time but had been introduced by Digital<ref>{{cite book|url=https://archive.org/details/bitsavers_decpdp11rsSICPLUSLangManOct72_10455777|title=BASIC-PLUS Language Manual|publisher=Digital Equipment Corporation|year=1972|location=Maynard, Massachusetts|type=PDF|pages=3–13|ref=CITEREFPLUS1972}}</ref> and copied by Microsoft.