HCoop / jackhill / mal.git / blame
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1 | # Introduction |
| 2 | ||
| 3 | This is a (partial) implementation of mal in BBC BASIC V. While there | |
| 4 | is already an implementation of mal in BASIC (in the "basic" | |
| 5 | directory), it's targeted at much more primitive versions of BASIC and | |
| 6 | relies on a pre-processor, both of which make it fairly un-idiomatic | |
| 7 | as a BBC BASIC V program. | |
| 8 | ||
| 9 | BBC BASIC V is the version of BBC BASIC supplied with the first | |
| 10 | ARM-based computers. It has substantial enhancements from the | |
| 11 | 6502-based versions of BBC BASIC, which were themselves at the | |
| 12 | advanced end of 8-bit BASICs. Mal uses many of the advanced features | |
| 13 | of BBC BASIC V and porting it to older versions would be difficult. | |
| 14 | ||
| 15 | Mal is intended to run on all versions of BBC BASIC V and BBC BASIC | |
| 16 | VI, as well as on Brandy 1.20.1. For compatibility with Brandy, it | |
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17 | avoids operating system calls where possible. The only exception |
| 18 | is that is has separate mechanisms for reading command-line arguments | |
| 19 | under Brandy and RISC OS. | |
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20 | |
| 21 | # Interesting features | |
| 22 | ||
| 8b4405de | 23 | This appears to be the first mal implementation that uses an table-driven |
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24 | deterministic finite automoton (a state machine) to implement its |
| 25 | tokenizer. | |
| 26 | ||
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27 | The mal heap is represented as a large array of fixed-size objects. |
| 28 | Lists and vectors are linked lists of these objects, while hash-maps | |
| 29 | are crit-bit trees. | |
| 30 | ||
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31 | Mal exceptions are implemented as BBC BASIC errors. Errors generated |
| 32 | by mal are numbered from &40E80900. | |
| 33 | ||
| 34 | ## Assigned error numbers | |
| 35 | ||
| 36 | No.| Description | |
| 37 | ---|------------ | |
| 38 | &00| Native mal error generated by 'throw' | |
| 39 | &1x| Object not of type 'x' | |
| 40 | &1F| Miscellaneous type mismatch | |
| 41 | &20| Invalid operation on empty list | |
| 42 | &21| Wrong number of arguments to function | |
| 43 | &22| Undefined symbol | |
| 44 | &23| Subscript out of range | |
| 45 | &24| Invalid 'catch*' clause | |
| 46 | &30| Unexpected end of input | |
| 47 | &31| Unexpected ')' | |
| 48 | &32| Hash-map key mush be a string | |
| 49 | &40| File not found | |
| 50 | &Fx| Internal errors (indicating a bug in mal) | |
| 51 | &F0| Unprintable value | |
| 52 | &F1| Call to non-existent core function |