The FX-801P is one of the more unusual BASIC-programmable calculators from Casio. On the one hand, it is a de luxe model with built-in tape drive and thermal printer; on the other hand, its limited memory and idiosyncratic BASIC suggest that it must be one of the earliest models in this product line. (I do not know for a fact how early; this is therefore just an educated guess.)

Just how idiosyncratic is its BASIC? How about non-standard keywords like INP or PRT. How about the almost unique feature of offering even hyperbolic functions as BASIC keywords (e.g., HSN for the hyperbolic sine.) How about features such as not requiring the argument of a univariate function to be enclosed on parentheses (e.g., you can write SIN X, you do not need to write SIN(X)), yet the multiplication sign, which can often be omitted on machines with similar syntax, is always required here (i.e., you cannot substitute 3X for 3*X).

Perhaps the biggest limitation of the FX-801P is its 1680 byte memory. This limitation of course is offset by the presence of a tape drive that appears to be very reliable; in my 20-year old, fairly used FX-801P, the tape drive still operates flawlessly.

Demonstrating the FX-801P's programming model is the following implementation of the logarithm of the Gamma function, computed using the Lanczos-approximation:

10 INP Z
20 S=SGN Z
30 Z=ABS Z
40 G=2.506628275635
50 G=G+225.5255846192/Z
60 G=G-268.2959738413/(Z+1)
70 G=G+80.90308069346/(Z+2)
80 G=G-5.007578639705/(Z+3)
90 G=G+.01146848954348/(Z+4)
100 G=LN G+(Z-.5)*LN (Z+4.65)-Z-4.65
110 IF S>0 THEN 130
120 G=LN(-π/Z/SIN (π*Z))-G
130 PRT G,EXP G