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The address of this routine is found in the parameter table.
During syntax checking a DEF FN statement is checked to ensure that it has the correct form. Space is also made available for the result of evaluating the function.
But in 'run-time' a DEF FN statement is passed by.
A Code of the next character in the statement
DEF_FN 08032 CALL SYNTAX_Z Jump forward if checking syntax.
08035 JR Z,DEF_FN_1
08037 LD A,206 Otherwise pass by the 'DEF FN' statement.
08039 JP PASS_BY
First consider the variable of the function.
DEF_FN_1 08042 SET 6,(IY+1) Signal 'a numeric variable' (set bit 6 of FLAGS).
08046 CALL ALPHA Check that the present code is a letter.
08049 JR NC,DEF_FN_4 Jump forward if not.
08051 RST 32 Fetch the next character.
08052 CP "$" Jump forward unless it is a '$'.
08054 JR NZ,DEF_FN_2
08056 RES 6,(IY+1) Reset bit 6 of FLAGS as it is a string variable.
08060 RST 32 Fetch the next character.
DEF_FN_2 08061 CP "(" A '(' must follow the variable's name.
08063 JR NZ,DEF_FN_7
08065 RST 32 Fetch the next character.
08066 CP ")" Jump forward if it is a ')' as there are no parameters of the function.
08068 JR Z,DEF_FN_6
A loop is now entered to deal with each parameter in turn.
DEF_FN_3 08070 CALL ALPHA The present code must be a letter.
08076 EX DE,HL Save the pointer in DE.
08077 RST 32 Fetch the next character.
08078 CP "$" Jump forward unless it is a '$'.
08080 JR NZ,DEF_FN_5
08082 EX DE,HL Otherwise save the new pointer in DE instead.
08083 RST 32 Fetch the next character.
DEF_FN_5 08084 EX DE,HL Move the pointer to the last character of the name to the HL register pair.
08085 LD BC,6 Now make six locations after that last character and enter a 'number marker' into the first of the new locations.
08091 INC HL
08092 INC HL
08093 LD (HL),14
08095 CP "," If the present character is a ',' then jump back as there should be a further parameter; otherwise jump out of the loop.
08097 JR NZ,DEF_FN_6
08099 RST 32
08100 JR DEF_FN_3
Next the definition of the function is considered.
DEF_FN_6 08102 CP ")" Check that the ')' does exist.
08104 JR NZ,DEF_FN_7
08106 RST 32 The next character is fetched.
08107 CP "=" It must be an '='.
08109 JR NZ,DEF_FN_7
08111 RST 32 Fetch the next character.
08112 LD A,(23611) Save the nature - numeric or string - of the variable (bit 6 of FLAGS).
08115 PUSH AF
08116 CALL SCANNING Now consider the definition as an expression.
08119 POP AF Fetch the nature of the variable and check that it is of the same type as found for the definition (specified by bit 6 of FLAGS).
08120 XOR (IY+1)
08123 AND 64
DEF_FN_7 08125 JP NZ,REPORT_C Give an error report if it is required.
08128 CALL CHECK_END Exit via CHECK_END (thereby moving on to consider the next statement in the line).
This routine continues into UNSTACK_Z.
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