5.1 Reader and frontend🔗ℹ

The frontend is split across four files:

• "intercal.rkt": reader entrypoint that produces a Racket module and exports intercal-main.

• "ick-lexer.rkt": tokenization and packed-SUB preprocessing.

• "ick-bnf.rkt": brag grammar for INTERCAL statements and expressions.

• "ick-normalize.rkt": conversion from brag parse trees to the normalized S-expression representation used by the macro backend.

The reader also shares the cleaning logic in "sick.rkt" to:

• merge continuation lines.

• discard prose/commentary lines that are not parseable statements.

• preserve upstream-style prefixes like DON’T and wrapped expressions.

5.2 Statements and modifiers🔗ℹ

This implementation supports:

• assignment, including BY-dimensioned arrays.

• NEXT, RESUME, FORGET, and COME FROM.

• READ OUT and WRITE IN.

• STASH, RETRIEVE, IGNORE, and REMEMBER.

• ABSTAIN and REINSTATE, including gerund lists.

• TRY AGAIN, GIVE UP, and NOTHING.

• prefix modifiers such as PLEASE, DO, NOT, and chance execution.

• postfix state modifiers ONCE and AGAIN.

Gerund-based abstention is implemented with counted abstention state, so multiple layers of abstention compose properly and a later reinstate removes one layer at a time.

5.3 Expressions and data🔗ℹ

The expression language includes:

• onespot and twospot constants.

• onespot, twospot, tail, and hybrid variables.

• MINGLE, SELECT, and unary binary operators.

• quote-based grouping.

• packed and nested SUB expressions.

• multidimensional arrays with runtime bounds checking.

The runtime enforces onespot/twospot width limits and raises the appropriate INTERCAL errors when a value does not fit.

5.4 I/O🔗ℹ

Scalar I/O uses the standard numeric INTERCAL spelling and Roman numeral output. Array I/O uses the C-INTERCAL tape encoding, which is necessary for real programs such as "pit/hello.i" and "pit/unlambda.i".

5.5 Libraries🔗ℹ

The macro frontend loads "syslib.i" automatically and pulls in additional libraries such as "pit/floatlib.i" when label references require them. Library inclusion is based on referenced labels, not on raw numeric constants, to avoid spurious loads.