TI BASIC (TI 99/4A)

TI BASIC is an ANSI-compliant BASIC programming language interpreter built into the 1981 Texas Instruments TI-99/4A home computer and its predecessor, the TI-99/4 (1979). TI Basic is based on Dartmouth BASIC and complies to the American National Standard for minimal Basic (ANSI X3.60-1978). 
Text, full screen graphics, logic operations, and recording to tape or any other file system, were supported by TI BASIC. Texas Instruments also produced TI Extended BASIC cartridge that enhanced the functionality accessible to BASIC users.
Elements of TI BASIC.
Statements.
The statements of TI BASIC are CALL, CLOSE, DATA, DEF, DIM, DISPLAY, END, FOR..TO..STEP, GOSUB, GOTO, IF..THEN..ELSE, INPUT, LET, NEXT, ON..GOSUB, ON..GOTO, OPEN, OPTION BASE, PRINT, RANDOMIZE, READ, REM, RESTORE, RETURN, STOP
Every line of TI BASIC can only contain one statement. The possibility to put several statements in a line with :: and also the necessary PEEK and LOAD calls to use assembly language routines became available in TI Extended BASIC. Note that there is no POKE statement in TI BASIC. Loading and executing machine code requires a 32K memory expansion and the TI Editor/Assembler or TI Mini Memory cartridge, which then gives access CALL LOAD. The 256 Bytes of RAM "directly" accessible by the CPU was mostly consumed by the BASIC interpreter. TI BASIC stored and ran programs from the 16K video RAM, and, unlike TI Extended BASIC, could not take advantage of the 32K memory expansion.
Functions.
Unlike Microsoft BASICs, which used LEFT$, MID$, RIGHT$, and INSTR for manipulating strings, TI BASIC used the ANSI-compliant SEG$ and POS.
Subprograms.
Subprograms are called with CALL statement (e.g. CALL CLEAR). There are no user defined subprograms (this is possible in TI Extended BASIC), but some subprograms are predefined:
Development.
Texas Instruments designed a virtual machine with a language or intermediate representation called GPL, for "Graphic Programming Language". TI BASIC was written in GPL, which is unique to the TI-99 line.
Although widely blamed for the slow performance of TI-BASIC, part of the problem is that the virtual machine is stored in graphics ROM, which has a slow 8-bit interface.) TI Extended BASIC improved execution speed by providing some functionality in assembly language and the ability to concatenate multiple statements in a single line of code.