SNAP (programming language)

SNAP allowed multiple statements to be placed on a single line, and used the period as the statement separator. This produced code that looked like English sentences, and was generally organized into blocks that looked like paragraphs.[8]

SNAP did not use line numbers for editing, and instead used in-code labels for branch targets, as was the case in FORTRAN. In SNAP, a label could be placed anywhere in the code by surrounding the textual name in parentheses like (FIRST LABEL). Labels were not separate statements, and did not require a period after them.[9]

Variables names could contain spaces, which is relatively rare for programming languages even today. Variables could hold strings or numbers, but different syntax was used to assign each one. For numbers, a simple syntax was used, SET I TO 1. SET was also used to perform mathematical operations, like SET I TO THE PRODUCT OF 10 AND J. A simpler syntax was offered for the more common increment and decrement operations, INCREASE M BY 1. or DECREASE M BY 2.[9]

For strings, a longer syntax was typically used, CALL "THIS IS A STRING" THE NEWSTRING. Substrings were accessed using a HyperTalk-like syntax by referring to the ordinal position, for instance, CALL THE J-TH CHARACTER OF NEWSTRING THE NEWCHAR., or CALL THE M-TH THROUGH N-TH CHARACTERS OF THE INPUT THE OUTPUT.[9]

SNAP also offered array-like collections known as "lists". Internally, these were stored as comma-delimited strings. Most of the string-related commands could be used to work with these by adding THE ... LIST. to the end. For instance, one could read a series of cards using READ THE CARD LIST., which would read each card as a separate string into the CARD variable. Items within a list were accessed using the same ordinal syntax, for instance PRINT THE 5-TH CARD, or COPY "NEW STRING" AND CALL IT THE 7-TH CARD. Lists of numbers could be created using SET THE NUMBER LIST TO 1,2,3,4,5.[10]

String variables can also be used as lists, or arrays. This was accomplished using the same ordinal position syntax but referring to the variable name and not the CHARACTER. For instance, CALL "HELLO" THE 1-ST PART. CALL "WORLD" THE 2-ND PART. would create an array called PART with two strings in it.[9]

An important point of the SNAP system is that the CALL statement is not static; it does not define KEY as the character at location J when it is encountered in the code, but when any following code accesses KEY. For instance, SET J TO 1. PRINT KEY. INCREASE J BY 1. PRINT KEY. would result in two different strings being printed. In this fashion, CALL has more in common with the BASIC programming language's DEF FN user-defined functions than it does with the SET statement, which is static.[11]

A static copy of a string could be made by COPY OLDSTRING, AND CALL IT NEWSTRING. Other string functions included APPEND one string TO another string., OVERWRITE string-expression ON THE M-TH [AND SUBSEQUENT] CHARACTER[S] OF string-name., DELETE THE M-TH [THROUGH N-TH] CHARACTER[S] OF string-name. and INSERT string-expression (BEFORE|AFTER) THE M-TH CHARACTER OF string-name.[12]

Unconditional branches were called using CONTINUE, for instance, CONTINUE WITH THE FIRST LABEL. There was also the alternative form REPEAT THE FIRST LABEL.. There was no difference between them, although the context of the surrounding code generally meant one form or the other was more natural to read. One could also refer to the start of the program with CONTINUE FROM THE BEGINNING. "As follows" could be used to refer to the next statement, CONTINUE AS FOLLOWS., which could be used to clarify branches.[13]

Conditional branches used an if–then(–else) structure:

 IF J IS LESS THAN 80 INCREASE J BY 1, AND REPEAT FROM THE FIRST LABEL, OTHERWISE CONTINUE AS FOLLOWS.

As in most languages, the OTHERWISE section was optional. Note the use of AND to make a compound statement within the then section, offering a block structure. For string comparisons, one used IS or the optional IS THE SAME AS.[12]

SNAP included a number of other keywords that had no behaviour of their own that were added simply for syntactic sugar. Among them were THE, A, FROM which the programmer could add in many locations to make the syntax more readable. Typical uses included READ A RECORD and REPEAT FROM THE LOOP START.[13]

From A Natural Language.[6] Variables and expressions are in italic. Optional forms are separated by vertical bars, |. Braces surround optional items, while angle-brackets surround required items that have more than one form. value refers to a numeric constant or variable, string to a quote-delimited string constant or string variable.

Flow control:

(string constant)

defines a program label

<CONTINUE|REPEAT> [WITH|FROM] <label|THE BEGINNING [OF THE PROCEDURE]|THE NEXT SENTENCE|AS FOLLOWS>

jump to the named label, the start of the program, or continue on to the next statement

IF value|string <IS|ARE> [THE SAME AS] value|string expression[,AND expression...] [, OTHERWISE expression[,AND expression...]]

if-then-else construct, with any number of expressions within the then and else sections

-string comparisons allowed substring tests like IS THE value[-TH] AND [SUBSEQUENT|PRECEDENT] CHARACTERS OF string

-numeric comparisons included EQUAL TO, LESS THAN, GREATER THAN, UNEQUAL TO, GREATER THAN OR EQUAL TO, LESS THAN OR EQUAL TO

-the end-of-file could be tested with IF THE INPUT IS EXHAUSTED.

TERMINATE

stops the program

EXECUTE

runs the program. Was to be expanded to allow execution to start at a given label, but was not implemented in the versions described in the references

Mathematics:

SET numeric variable TO value - assigns a value to a numeric variable

SET numeric variable TO THE [SUM|DIFFERENCE|PRODUCT|QUOTIENT|REMAINDER|CEILING|GREATER|LESSER] OF value AND value

perform mathematical functions with two operands

INCREASE variable BY value - simplified notation for addition

DECREASE variable BY value - ...and subtraction

String manipulation:

CALL string [THE] string variable - create a string function

[FORM A] COPY [OF] string AND CALL IT [THE] string variable - copy a string from one variable to another

APPEND string TO string variable - append a string variable with another string

LINK string TO string - appends the first string to the second, but does not copy it, future changes to the second string will be tracked as in a CALL

DELETE THE value[-TH] [THROUGH value [-TH]] CHARACTER[S] OF string variable - trim a string from the selected character on, or a given range

OVERWRITE string ON THE value[-TH] [AND SUBSEQUENT|PRECEDENT] CHARACTER[S] OF string variable - replaces one character of a string with another, or that character and those running forward or backward from the selected position.

Input/output related:

SELECT number [FOR <INPUT|OUTPUT>]

used to select a device for other input/output operations

READ [A|THE] string variable

reads a single punch card

REQUEST [A|THE] string variable

asks for user input from the console

FETCH [A|THE] string variable

reads one record from the most recently SELECTed device

PRINT [A|THE] variable

sends output to the line printer

TYPE [A|THE] variable

sends output to the console

PUNCH [A|THE] variable

sends output to the card punch

PERFORATE [A|THE] variable

sends output to paper tape

WRITE [A|THE] variable

sends data to the last SELECTed device

Others:

CONTROL various

a temporary command used to control the language as new features were added

RESERVE SPACE FOR number <CHARACTERS IN variable|ELEMENTS IN [THE] variable LIST

similar to the DIM statement in BASIC, sets aside a specified amount of memory to hold a string, or a given number of strings from a list. Using RESERVE avoided memory operations as the string or list was built and improved performance

• Barnett, Michael; Ruhsam, William (May 1969). Harrison Fuller (ed.). SNAP: an experiment in natural language programming. AFIPS '69, Spring Joint Conference. Boston. pp. 75–87. doi:10.1145/1476793.1476815.
• Barnett, Michael; Ruhsam, William (August 1968). "A Natural Language Programming System for Text Processing". IEEE Transactions on Engineering Writing and Speech. 11 (2): 45–52. doi:10.1109/TEWS.1968.4322334. JSTOR 30199362. S2CID 51670564.
• Barnett, Michael (March 1970). "SNAP: A Programming Language for Humanists". Computers and the Humanities. 4 (4): 225–240. doi:10.1109/TEWS.1968.4322334. JSTOR 30199362. S2CID 51670564.

• Barnett, Michael (1969). Computer Programming in English. Harcourt, Brace & World. OL 5754250M.